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GNU Guix
********

This document describes GNU Guix version VERSION, a functional package management tool written for the GNU system.

This manual is also available in Simplified Chinese (see GNU Guix参考手册), French (see Manuel de référence de GNU Guix), German (see Referenzhandbuch zu GNU Guix), Spanish (see Manual de referencia de GNU Guix), Brazilian Portuguese (see Manual de referência do GNU Guix), and Russian (see Руководство GNU Guix).  If you would like to translate it in your native language, consider joining Weblate (https://translate.fedoraproject.org/projects/guix/documentation-manual) (see Translating Guix).

Introduction
************

GNU Guix (``Guix'' is pronounced like ``geeks'', or ``ɡiːks'' using the international phonetic alphabet (IPA).) is a package management tool for and distribution of the GNU system. Guix makes it easy for unprivileged users to install, upgrade, or remove software packages, to roll back to a previous package set, to build packages from source, and generally assists with the creation and maintenance of software environments.

You can install GNU Guix on top of an existing GNU/Linux system where it complements the available tools without interference (see Installation), or you can use it as a standalone operating system distribution, Guix System (We used to refer to Guix System as ``Guix System Distribution'' or ``GuixSD''.  We now consider it makes more sense to group everything under the ``Guix'' banner since, after all, Guix System is readily available through the guix system command, even if you're using a different distro underneath!).  See GNU Distribution.

Managing Software the Guix Way
==============================

Guix provides a command-line package management interface (see Package Management), tools to help with software development (see Development), command-line utilities for more advanced usage (see Utilities), as well as Scheme programming interfaces (see Programming Interface). Its build daemon is responsible for building packages on behalf of users (see Setting Up the Daemon) and for downloading pre-built binaries from authorized sources (see Substitutes).

Guix includes package definitions for many GNU and non-GNU packages, all of which respect the user's computing freedom (https://www.gnu.org/philosophy/free-sw.html).  It is extensible: users can write their own package definitions (see Defining Packages) and make them available as independent package modules (see Package Modules).  It is also customizable: users can derive specialized package definitions from existing ones, including from the command line (see Package Transformation Options).

Under the hood, Guix implements the functional package management discipline pioneered by Nix (see Acknowledgments). In Guix, the package build and installation process is seen as a function, in the mathematical sense.  That function takes inputs, such as build scripts, a compiler, and libraries, and returns an installed package.  As a pure function, its result depends solely on its inputs---for instance, it cannot refer to software or scripts that were not explicitly passed as inputs.  A build function always produces the same result when passed a given set of inputs.  It cannot alter the environment of the running system in any way; for instance, it cannot create, modify, or delete files outside of its build and installation directories.  This is achieved by running build processes in isolated environments (or containers), where only their explicit inputs are visible.

The result of package build functions is cached in the file system, in a special directory called the store (see The Store).  Each package is installed in a directory of its own in the store---by default under /gnu/store.  The directory name contains a hash of all the inputs used to build that package; thus, changing an input yields a different directory name.

This approach is the foundation for the salient features of Guix: support for transactional package upgrade and rollback, per-user installation, and garbage collection of packages (see Features).

GNU Distribution
================

Guix comes with a distribution of the GNU system consisting entirely of free software (The term ``free'' here refers to the freedom provided to users of that software (https://www.gnu.org/philosophy/free-sw.html).).  The distribution can be installed on its own (see System Installation), but it is also possible to install Guix as a package manager on top of an installed GNU/Linux system (see Installation).  When we need to distinguish between the two, we refer to the standalone distribution as Guix System.

The distribution provides core GNU packages such as GNU libc, GCC, and Binutils, as well as many GNU and non-GNU applications.  The complete list of available packages can be browsed on-line (https://www.gnu.org/software/guix/packages) or by running guix package (see Invoking guix package):

     guix package --list-available

Our goal is to provide a practical 100% free software distribution of Linux-based and other variants of GNU, with a focus on the promotion and tight integration of GNU components, and an emphasis on programs and tools that help users exert that freedom.

Packages are currently available on the following platforms:

x86_64-linux
     Intel/AMD x86_64 architecture, Linux-Libre kernel.

i686-linux
     Intel 32-bit architecture (IA32), Linux-Libre kernel.

armhf-linux
     ARMv7-A architecture with hard float, Thumb-2 and NEON, using the EABI hard-float application binary interface (ABI), and Linux-Libre kernel.

aarch64-linux
     little-endian 64-bit ARMv8-A processors, Linux-Libre kernel.

i586-gnu
     GNU/Hurd (https://hurd.gnu.org) on the Intel 32-bit architecture (IA32).

     This configuration is experimental and under development.  The easiest way for you to give it a try is by setting up an instance of hurd-vm-service-type on your GNU/Linux machine (see hurd-vm-service-type). See Contributing, on how to help!

mips64el-linux (unsupported)
     little-endian 64-bit MIPS processors, specifically the Loongson series, n32 ABI, and Linux-Libre kernel.  This configuration is no longer fully supported; in particular, there is no ongoing work to ensure that this architecture still works.  Should someone decide they wish to revive this architecture then the code is still available.

powerpc-linux (unsupported)
     big-endian 32-bit PowerPC processors, specifically the PowerPC G4 with AltiVec support, and Linux-Libre kernel.  This configuration is not fully supported and there is no ongoing work to ensure this architecture works.

powerpc64le-linux
     little-endian 64-bit Power ISA processors, Linux-Libre kernel.  This includes POWER9 systems such as the RYF Talos II mainboard (https://www.fsf.org/news/talos-ii-mainboard-and-talos-ii-lite-mainboard-now-fsf-certified-to-respect-your-freedom). This platform is available as a "technology preview": although it is supported, substitutes are not yet available from the build farm (see Substitutes), and some packages may fail to build (see Tracking Bugs and Changes).  That said, the Guix community is actively working on improving this support, and now is a great time to try it and get involved!

riscv64-linux
     little-endian 64-bit RISC-V processors, specifically RV64GC, and Linux-Libre kernel. This platform is available as a "technology preview": although it is supported, substitutes are not yet available from the build farm (see Substitutes), and some packages may fail to build (see Tracking Bugs and Changes).  That said, the Guix community is actively working on improving this support, and now is a great time to try it and get involved!

With Guix System, you declare all aspects of the operating system configuration and Guix takes care of instantiating the configuration in a transactional, reproducible, and stateless fashion (see System Configuration).  Guix System uses the Linux-libre kernel, the Shepherd initialization system (see Introduction (The GNU Shepherd Manual)), the well-known GNU utilities and tool chain, as well as the graphical environment or system services of your choice.

Guix System is available on all the above platforms except mips64el-linux, powerpc-linux, powerpc64le-linux and riscv64-linux.

For information on porting to other architectures or kernels, see Porting.

Building this distribution is a cooperative effort, and you are invited to join!  See Contributing, for information about how you can help.

Installation
************

     We recommend the use of this shell installer script (https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh) to install Guix on top of a running GNU/Linux system, thereafter called a foreign distro. (This section is concerned with the installation of the package manager, which can be done on top of a running GNU/Linux system.  If, instead, you want to install the complete GNU operating system, see System Installation.) The script automates the download, installation, and initial configuration of Guix.  It should be run as the root user.

When installed on a foreign distro, GNU Guix complements the available tools without interference.  Its data lives exclusively in two directories, usually /gnu/store and /var/guix; other files on your system, such as /etc, are left untouched.

Once installed, Guix can be updated by running guix pull (see Invoking guix pull).

If you prefer to perform the installation steps manually or want to tweak them, you may find the following subsections useful.  They describe the software requirements of Guix, as well as how to install it manually and get ready to use it.

Binary Installation
===================

This section describes how to install Guix on an arbitrary system from a self-contained tarball providing binaries for Guix and for all its dependencies.  This is often quicker than installing from source, which is described in the next sections.  The only requirement is to have GNU tar and Xz.

     We recommend the use of this shell installer script (https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh).  The script automates the download, installation, and initial configuration steps described below.  It should be run as the root user.  As root, you can thus run this:

          cd /tmp
          wget https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh
          chmod +x guix-install.sh
          ./guix-install.sh

     If you're running Debian or a derivative such as Ubuntu, you can instead install the package (it might be a version older than VERSION but you can update it afterwards by running guix pull):

          sudo apt install guix

     Likewise on openSUSE:

          sudo zypper install guix

     When you're done, see Application Setup for extra configuration you might need, and Getting Started for your first steps!

Installing goes along these lines:

 1. Download the binary tarball from https://ftp.gnu.org/gnu/guix/guix-binary-VERSION.x86_64-linux.tar.xz, where x86_64-linux can be replaced with i686-linux for an i686 (32-bits) machine already running the kernel Linux, and so on (see GNU Distribution).

     Make sure to download the associated .sig file and to verify the authenticity of the tarball against it, along these lines:

          $ wget https://ftp.gnu.org/gnu/guix/guix-binary-VERSION.x86_64-linux.tar.xz.sig
          $ gpg --verify guix-binary-VERSION.x86_64-linux.tar.xz.sig

     If that command fails because you do not have the required public key, then run this command to import it:

          $ wget 'https://sv.gnu.org/people/viewgpg.php?user_id=15145' \
                -qO - | gpg --import -

     and rerun the gpg --verify command.

     Take note that a warning like ``This key is not certified with a trusted signature!'' is normal.

 2. Now, you need to become the root user.  Depending on your distribution, you may have to run su - or sudo -i.  As root, run:

          # cd /tmp
          # tar --warning=no-timestamp -xf \
               /path/to/guix-binary-VERSION.x86_64-linux.tar.xz
          # mv var/guix /var/ && mv gnu /

     This creates /gnu/store (see The Store) and /var/guix. The latter contains a ready-to-use profile for root (see next step).

     Do not unpack the tarball on a working Guix system since that would overwrite its own essential files.

     The --warning=no-timestamp option makes sure GNU tar does not emit warnings about ``implausibly old time stamps'' (such warnings were triggered by GNU tar 1.26 and older; recent versions are fine). They stem from the fact that all the files in the archive have their modification time set to 1 (which means January 1st, 1970).  This is done on purpose to make sure the archive content is independent of its creation time, thus making it reproducible.

 3. Make the profile available under ~root/.config/guix/current, which is where guix pull will install updates (see Invoking guix pull):

          # mkdir -p ~root/.config/guix
          # ln -sf /var/guix/profiles/per-user/root/current-guix \
                   ~root/.config/guix/current

     Source etc/profile to augment PATH and other relevant environment variables:

          # GUIX_PROFILE="`echo ~root`/.config/guix/current" ; \
            source $GUIX_PROFILE/etc/profile

 4. Create the group and user accounts for build users as explained below (see Build Environment Setup).

 5. Run the daemon, and set it to automatically start on boot.

     If your host distro uses the systemd init system, this can be achieved with these commands:

          # cp ~root/.config/guix/current/lib/systemd/system/gnu-store.mount \
               ~root/.config/guix/current/lib/systemd/system/guix-daemon.service \
               /etc/systemd/system/
          # systemctl enable --now gnu-store.mount guix-daemon

     You may also want to arrange for guix gc to run periodically:

          # cp ~root/.config/guix/current/lib/systemd/system/guix-gc.service \
               ~root/.config/guix/current/lib/systemd/system/guix-gc.timer \
               /etc/systemd/system/
          # systemctl enable --now guix-gc.timer

     You may want to edit guix-gc.service to adjust the command line options to fit your needs (see Invoking guix gc).

     If your host distro uses the Upstart init system:

          # initctl reload-configuration
          # cp ~root/.config/guix/current/lib/upstart/system/guix-daemon.conf \
               /etc/init/
          # start guix-daemon

     Otherwise, you can still start the daemon manually with:

          # ~root/.config/guix/current/bin/guix-daemon \
                 --build-users-group=guixbuild

 6. Make the guix command available to other users on the machine, for instance with:

          # mkdir -p /usr/local/bin
          # cd /usr/local/bin
          # ln -s /var/guix/profiles/per-user/root/current-guix/bin/guix

     It is also a good idea to make the Info version of this manual available there:

          # mkdir -p /usr/local/share/info
          # cd /usr/local/share/info
          # for i in /var/guix/profiles/per-user/root/current-guix/share/info/* ;
            do ln -s $i ; done

     That way, assuming /usr/local/share/info is in the search path, running info guix will open this manual (see Other Info Directories (GNU Texinfo), for more details on changing the Info search path).

 7. To use substitutes from ci.guix.gnu.org, bordeaux.guix.gnu.org or a mirror (see Substitutes), authorize them:

          # guix archive --authorize < \
               ~root/.config/guix/current/share/guix/ci.guix.gnu.org.pub
          # guix archive --authorize < \
               ~root/.config/guix/current/share/guix/bordeaux.guix.gnu.org.pub

          If you do not enable substitutes, Guix will end up building everything from source on your machine, making each installation and upgrade very expensive.  See On Trusting Binaries, for a discussion of reasons why one might want do disable substitutes.

 8. Each user may need to perform a few additional steps to make their Guix environment ready for use, see Application Setup.

Voilà, the installation is complete!

You can confirm that Guix is working by installing a sample package into the root profile:

     # guix install hello

The binary installation tarball can be (re)produced and verified simply by running the following command in the Guix source tree:

     make guix-binary.SYSTEM.tar.xz

... which, in turn, runs:

     guix pack -s SYSTEM --localstatedir \
       --profile-name=current-guix guix

See Invoking guix pack, for more info on this handy tool.

Requirements
============

This section lists requirements when building Guix from source.  The build procedure for Guix is the same as for other GNU software, and is not covered here.  Please see the files README and INSTALL in the Guix source tree for additional details.

GNU Guix is available for download from its website at https://www.gnu.org/software/guix/.

GNU Guix depends on the following packages:

  * GNU Guile (https://gnu.org/software/guile/), version 3.0.x, version 3.0.3 or later;

  * Guile-Gcrypt (https://notabug.org/cwebber/guile-gcrypt), version 0.1.0 or later;

  * Guile-GnuTLS (https://gitlab.com/gnutls/guile/) (see how to install the GnuTLS bindings for Guile (GnuTLS-Guile)) (The Guile bindings to GnuTLS (https://gnutls.org/) were distributed as part of GnuTLS until version 3.7.8 included.);

  * Guile-SQLite3 (https://notabug.org/guile-sqlite3/guile-sqlite3), version 0.1.0 or later;

  * Guile-zlib (https://notabug.org/guile-zlib/guile-zlib), version 0.1.0 or later;

  * Guile-lzlib (https://notabug.org/guile-lzlib/guile-lzlib);

  * Guile-Avahi (https://www.nongnu.org/guile-avahi/);

  * Guile-Git (https://gitlab.com/guile-git/guile-git), version 0.5.0 or later;

  * Git (https://git-scm.com) (yes, both!);

  * Guile-JSON (https://savannah.nongnu.org/projects/guile-json/) 4.3.0 or later;

  * GNU Make (https://www.gnu.org/software/make/).

The following dependencies are optional:

  * Support for build offloading (see Daemon Offload Setup) and guix copy (see Invoking guix copy) depends on Guile-SSH (https://github.com/artyom-poptsov/guile-ssh), version 0.13.0 or later.

  * Guile-zstd (https://notabug.org/guile-zstd/guile-zstd), for zstd compression and decompression in guix publish and for substitutes (see Invoking guix publish).

  * Guile-Semver (https://ngyro.com/software/guile-semver.html) for the crate importer (see Invoking guix import).

  * Guile-Lib (https://www.nongnu.org/guile-lib/doc/ref/htmlprag/) for the go importer (see Invoking guix import) and for some of the ``updaters'' (see Invoking guix refresh).

  * When libbz2 (http://www.bzip.org) is available, guix-daemon can use it to compress build logs.

Unless --disable-daemon was passed to configure, the following packages are also needed:

  * GNU libgcrypt (https://gnupg.org/);

  * SQLite 3 (https://sqlite.org);

  * GCC's g++ (https://gcc.gnu.org), with support for the C++11 standard.

When configuring Guix on a system that already has a Guix installation, be sure to specify the same state directory as the existing installation using the --localstatedir option of the configure script (see localstatedir (GNU Coding Standards)).  Usually, this LOCALSTATEDIR option is set to the value /var.  The configure script protects against unintended misconfiguration of LOCALSTATEDIR so you do not inadvertently corrupt your store (see The Store).  The configuration directory should also be configured by setting the --sysconfdir option to the /etc value, which is the location used by Guix to store for example the access control list of authorized machines and the definition of offload machines.

Running the Test Suite
======================

After a successful configure and make run, it is a good idea to run the test suite.  It can help catch issues with the setup or environment, or bugs in Guix itself---and really, reporting test failures is a good way to help improve the software.  To run the test suite, type:

     make check

Test cases can run in parallel: you can use the -j option of GNU make to speed things up.  The first run may take a few minutes on a recent machine; subsequent runs will be faster because the store that is created for test purposes will already have various things in cache.

It is also possible to run a subset of the tests by defining the TESTS makefile variable as in this example:

     make check TESTS="tests/store.scm tests/cpio.scm"

By default, tests results are displayed at a file level.  In order to see the details of every individual test cases, it is possible to define the SCM_LOG_DRIVER_FLAGS makefile variable as in this example:

     make check TESTS="tests/base64.scm" SCM_LOG_DRIVER_FLAGS="--brief=no"

The underlying SRFI 64 custom Automake test driver used for the 'check' test suite (located at build-aux/test-driver.scm) also allows selecting which test cases to run at a finer level, via its --select and --exclude options.  Here's an example, to run all the test cases from the tests/packages.scm test file whose names start with ``transaction-upgrade-entry'':

     export SCM_LOG_DRIVER_FLAGS="--select=^transaction-upgrade-entry"
     make check TESTS="tests/packages.scm"

Those wishing to inspect the results of failed tests directly from the command line can add the --errors-only=yes option to the SCM_LOG_DRIVER_FLAGS makefile variable and set the VERBOSE Automake makefile variable, as in:

     make check SCM_LOG_DRIVER_FLAGS="--brief=no --errors-only=yes" VERBOSE=1

The --show-duration=yes option can be used to print the duration of the individual test cases, when used in combination with --brief=no:

     make check SCM_LOG_DRIVER_FLAGS="--brief=no --show-duration=yes"

See Parallel Test Harness (GNU Automake) for more information about the Automake Parallel Test Harness.

Upon failure, please email bug-guix@gnu.org and attach the test-suite.log file.  Please specify the Guix version being used as well as version numbers of the dependencies (see Requirements) in your message.

Guix also comes with a whole-system test suite that tests complete Guix System instances.  It can only run on systems where Guix is already installed, using:

     make check-system

or, again, by defining TESTS to select a subset of tests to run:

     make check-system TESTS="basic mcron"

These system tests are defined in the (gnu tests ...) modules.  They work by running the operating systems under test with lightweight instrumentation in a virtual machine (VM).  They can be computationally intensive or rather cheap, depending on whether substitutes are available for their dependencies (see Substitutes). Some of them require a lot of storage space to hold VM images.

Again in case of test failures, please send bug-guix@gnu.org all the details.

Setting Up the Daemon
=====================

Operations such as building a package or running the garbage collector are all performed by a specialized process, the build daemon, on behalf of clients.  Only the daemon may access the store and its associated database.  Thus, any operation that manipulates the store goes through the daemon.  For instance, command-line tools such as guix package and guix build communicate with the daemon (via remote procedure calls) to instruct it what to do.

The following sections explain how to prepare the build daemon's environment.  See also Substitutes, for information on how to allow the daemon to download pre-built binaries.

Build Environment Setup
-----------------------

In a standard multi-user setup, Guix and its daemon---the guix-daemon program---are installed by the system administrator; /gnu/store is owned by root and guix-daemon runs as root.  Unprivileged users may use Guix tools to build packages or otherwise access the store, and the daemon will do it on their behalf, ensuring that the store is kept in a consistent state, and allowing built packages to be shared among users.

When guix-daemon runs as root, you may not want package build processes themselves to run as root too, for obvious security reasons.  To avoid that, a special pool of build users should be created for use by build processes started by the daemon. These build users need not have a shell and a home directory: they will just be used when the daemon drops root privileges in build processes.  Having several such users allows the daemon to launch distinct build processes under separate UIDs, which guarantees that they do not interfere with each other---an essential feature since builds are regarded as pure functions (see Introduction).

On a GNU/Linux system, a build user pool may be created like this (using Bash syntax and the shadow commands):

     # groupadd --system guixbuild
     # for i in $(seq -w 1 10);
       do
         useradd -g guixbuild -G guixbuild           \
                 -d /var/empty -s $(which nologin)   \
                 -c "Guix build user $i" --system    \
                 guixbuilder$i;
       done

The number of build users determines how many build jobs may run in parallel, as specified by the --max-jobs option (see --max-jobs).  To use guix system vm and related commands, you may need to add the build users to the kvm group so they can access /dev/kvm, using -G guixbuild,kvm instead of -G guixbuild (see Invoking guix system).

The guix-daemon program may then be run as root with the following command (If your machine uses the systemd init system, copying the PREFIX/lib/systemd/system/guix-daemon.service file to /etc/systemd/system will ensure that guix-daemon is automatically started.  Similarly, if your machine uses the Upstart init system, copy the PREFIX/lib/upstart/system/guix-daemon.conf file to /etc/init.):

     # guix-daemon --build-users-group=guixbuild

This way, the daemon starts build processes in a chroot, under one of the guixbuilder users.  On GNU/Linux, by default, the chroot environment contains nothing but:

  * a minimal /dev directory, created mostly independently from the host /dev (``Mostly'', because while the set of files that appear in the chroot's /dev is fixed, most of these files can only be created if the host has them.);

  * the /proc directory; it only shows the processes of the container since a separate PID name space is used;

  * /etc/passwd with an entry for the current user and an entry for user nobody;

  * /etc/group with an entry for the user's group;

  * /etc/hosts with an entry that maps localhost to 127.0.0.1;

  * a writable /tmp directory.

The chroot does not contain a /home directory, and the HOME environment variable is set to the non-existent /homeless-shelter.  This helps to highlight inappropriate uses of HOME in the build scripts of packages.

You can influence the directory where the daemon stores build trees via the TMPDIR environment variable.  However, the build tree within the chroot is always called /tmp/guix-build-NAME.drv-0, where NAME is the derivation name---e.g., coreutils-8.24. This way, the value of TMPDIR does not leak inside build environments, which avoids discrepancies in cases where build processes capture the name of their build tree.

The daemon also honors the http_proxy and https_proxy environment variables for HTTP and HTTPS downloads it performs, be it for fixed-output derivations (see Derivations) or for substitutes (see Substitutes).

If you are installing Guix as an unprivileged user, it is still possible to run guix-daemon provided you pass --disable-chroot. However, build processes will not be isolated from one another, and not from the rest of the system.  Thus, build processes may interfere with each other, and may access programs, libraries, and other files available on the system---making it much harder to view them as pure functions.

Using the Offload Facility
--------------------------

When desired, the build daemon can offload derivation builds to other machines running Guix, using the offload build hook (This feature is available only when Guile-SSH (https://github.com/artyom-poptsov/guile-ssh) is present.).  When that feature is enabled, a list of user-specified build machines is read from /etc/guix/machines.scm; every time a build is requested, for instance via guix build, the daemon attempts to offload it to one of the machines that satisfy the constraints of the derivation, in particular its system types---e.g., x86_64-linux. A single machine can have multiple system types, either because its architecture natively supports it, via emulation (see Transparent Emulation with QEMU), or both.  Missing prerequisites for the build are copied over SSH to the target machine, which then proceeds with the build; upon success the output(s) of the build are copied back to the initial machine.  The offload facility comes with a basic scheduler that attempts to select the best machine.  The best machine is chosen among the available machines based on criteria such as:

 1. The availability of a build slot.  A build machine can have as many build slots (connections) as the value of the parallel-builds field of its build-machine object.

 2. Its relative speed, as defined via the speed field of its build-machine object.

 3. Its load.  The normalized machine load must be lower than a threshold value, configurable via the overload-threshold field of its build-machine object.

 4. Disk space availability.  More than a 100 MiB must be available.

The /etc/guix/machines.scm file typically looks like this:

     (list (build-machine
             (name "eightysix.example.org")
             (systems (list "x86_64-linux" "i686-linux"))
             (host-key "ssh-ed25519 AAAAC3Nza...")
             (user "bob")
             (speed 2.))     ;incredibly fast!

           (build-machine
             (name "armeight.example.org")
             (systems (list "aarch64-linux"))
             (host-key "ssh-rsa AAAAB3Nza...")
             (user "alice")

             ;; Remember 'guix offload' is spawned by
             ;; 'guix-daemon' as root.
             (private-key "/root/.ssh/identity-for-guix")))

In the example above we specify a list of two build machines, one for the x86_64 and i686 architectures and one for the aarch64 architecture.

In fact, this file is---not surprisingly!---a Scheme file that is evaluated when the offload hook is started.  Its return value must be a list of build-machine objects.  While this example shows a fixed list of build machines, one could imagine, say, using DNS-SD to return a list of potential build machines discovered in the local network (see Guile-Avahi (Using Avahi in Guile Scheme Programs)).  The build-machine data type is detailed below.

 -- Data Type: build-machine
     This data type represents build machines to which the daemon may offload builds.  The important fields are:

     name
          The host name of the remote machine.

     systems
          The system types the remote machine supports---e.g., (list "x86_64-linux" "i686-linux").

     user
          The user account on the remote machine to use when connecting over SSH. Note that the SSH key pair must not be passphrase-protected, to allow non-interactive logins.

     host-key
          This must be the machine's SSH public host key in OpenSSH format. This is used to authenticate the machine when we connect to it.  It is a long string that looks like this:

               ssh-ed25519 AAAAC3NzaC...mde+UhL hint@example.org

          If the machine is running the OpenSSH daemon, sshd, the host key can be found in a file such as /etc/ssh/ssh_host_ed25519_key.pub.

          If the machine is running the SSH daemon of GNU lsh, lshd, the host key is in /etc/lsh/host-key.pub or a similar file.  It can be converted to the OpenSSH format using lsh-export-key (see Converting keys (LSH Manual)):

               $ lsh-export-key --openssh < /etc/lsh/host-key.pub
               ssh-rsa AAAAB3NzaC1yc2EAAAAEOp8FoQAAAQEAs1eB46LV...

     A number of optional fields may be specified:

     port (default: 22)
          Port number of SSH server on the machine.

     private-key (default: ~root/.ssh/id_rsa)
          The SSH private key file to use when connecting to the machine, in OpenSSH format.  This key must not be protected with a passphrase.

          Note that the default value is the private key of the root account.  Make sure it exists if you use the default.

     compression (default: "zlib@openssh.com,zlib")
     compression-level (default: 3)
          The SSH-level compression methods and compression level requested.

          Note that offloading relies on SSH compression to reduce bandwidth usage when transferring files to and from build machines.

     daemon-socket (default: "/var/guix/daemon-socket/socket")
          File name of the Unix-domain socket guix-daemon is listening to on that machine.

     overload-threshold (default: 0.8)
          The load threshold above which a potential offload machine is disregarded by the offload scheduler.  The value roughly translates to the total processor usage of the build machine, ranging from 0.0 (0%) to 1.0 (100%).  It can also be disabled by setting overload-threshold to #f.

     parallel-builds (default: 1)
          The number of builds that may run in parallel on the machine.

     speed (default: 1.0)
          A ``relative speed factor''.  The offload scheduler will tend to prefer machines with a higher speed factor.

     features (default: '())
          A list of strings denoting specific features supported by the machine. An example is "kvm" for machines that have the KVM Linux modules and corresponding hardware support.  Derivations can request features by name, and they will be scheduled on matching build machines.

     On Guix System, instead of managing /etc/guix/machines.scm independently, you can choose to specify build machines directly in the operating-system declaration, in the build-machines field of guix-configuration.  See build-machines field of guix-configuration.

The guix command must be in the search path on the build machines.  You can check whether this is the case by running:

     ssh build-machine guix repl --version

There is one last thing to do once machines.scm is in place.  As explained above, when offloading, files are transferred back and forth between the machine stores.  For this to work, you first need to generate a key pair on each machine to allow the daemon to export signed archives of files from the store (see Invoking guix archive):

     # guix archive --generate-key

     This key pair is not related to the SSH key pair that was previously mentioned in the description of the build-machine data type.

Each build machine must authorize the key of the master machine so that it accepts store items it receives from the master:

     # guix archive --authorize < master-public-key.txt

Likewise, the master machine must authorize the key of each build machine.

All the fuss with keys is here to express pairwise mutual trust relations between the master and the build machines.  Concretely, when the master receives files from a build machine (and vice versa), its build daemon can make sure they are genuine, have not been tampered with, and that they are signed by an authorized key.

To test whether your setup is operational, run this command on the master node:

     # guix offload test

This will attempt to connect to each of the build machines specified in /etc/guix/machines.scm, make sure Guix is available on each machine, attempt to export to the machine and import from it, and report any error in the process.

If you want to test a different machine file, just specify it on the command line:

     # guix offload test machines-qualif.scm

Last, you can test the subset of the machines whose name matches a regular expression like this:

     # guix offload test machines.scm '\.gnu\.org$'

To display the current load of all build hosts, run this command on the main node:

     # guix offload status

SELinux Support
---------------

Guix includes an SELinux policy file at etc/guix-daemon.cil that can be installed on a system where SELinux is enabled, in order to label Guix files and to specify the expected behavior of the daemon.  Since Guix System does not provide an SELinux base policy, the daemon policy cannot be used on Guix System.

Installing the SELinux policy
.............................

     The guix-install.sh binary installation script offers to perform the steps below for you (see Binary Installation).

To install the policy run this command as root:

     semodule -i /var/guix/profiles/per-user/root/current-guix/share/selinux/guix-daemon.cil

Then, as root, relabel the file system, possibly after making it writable:

     mount -o remount,rw /gnu/store
     restorecon -R /gnu /var/guix

At this point you can start or restart guix-daemon; on a distribution that uses systemd as its service manager, you can do that with:

     systemctl restart guix-daemon

Once the policy is installed, the file system has been relabeled, and the daemon has been restarted, it should be running in the guix_daemon_t context.  You can confirm this with the following command:

     ps -Zax | grep guix-daemon

Monitor the SELinux log files as you run a command like guix build hello to convince yourself that SELinux permits all necessary operations.

Limitations
...........

This policy is not perfect.  Here is a list of limitations or quirks that should be considered when deploying the provided SELinux policy for the Guix daemon.

 1. guix_daemon_socket_t isn’t actually used.  None of the socket operations involve contexts that have anything to do with guix_daemon_socket_t.  It doesn’t hurt to have this unused label, but it would be preferable to define socket rules for only this label.

 2. guix gc cannot access arbitrary links to profiles.  By design, the file label of the destination of a symlink is independent of the file label of the link itself.  Although all profiles under $localstatedir are labelled, the links to these profiles inherit the label of the directory they are in.  For links in the user’s home directory this will be user_home_t.  But for links from the root user’s home directory, or /tmp, or the HTTP server’s working directory, etc, this won’t work.  guix gc would be prevented from reading and following these links.

 3. The daemon’s feature to listen for TCP connections might no longer work. This might require extra rules, because SELinux treats network sockets differently from files.

 4. Currently all files with a name matching the regular expression /gnu/store/.+-(guix-.+|profile)/bin/guix-daemon are assigned the label guix_daemon_exec_t; this means that any file with that name in any profile would be permitted to run in the guix_daemon_t domain.  This is not ideal.  An attacker could build a package that provides this executable and convince a user to install and run it, which lifts it into the guix_daemon_t domain. At that point SELinux could not prevent it from accessing files that are allowed for processes in that domain.

     You will need to relabel the store directory after all upgrades to guix-daemon, such as after running guix pull.  Assuming the store is in /gnu, you can do this with restorecon -vR /gnu, or by other means provided by your operating system.

     We could generate a much more restrictive policy at installation time, so that only the exact file name of the currently installed guix-daemon executable would be labelled with guix_daemon_exec_t, instead of using a broad regular expression. The downside is that root would have to install or upgrade the policy at installation time whenever the Guix package that provides the effectively running guix-daemon executable is upgraded.

Invoking guix-daemon
====================

The guix-daemon program implements all the functionality to access the store.  This includes launching build processes, running the garbage collector, querying the availability of a build result, etc.  It is normally run as root like this:

     # guix-daemon --build-users-group=guixbuild

This daemon can also be started following the systemd ``socket activation'' protocol (see make-systemd-constructor (The GNU Shepherd Manual)).

For details on how to set it up, see Setting Up the Daemon.

By default, guix-daemon launches build processes under different UIDs, taken from the build group specified with --build-users-group.  In addition, each build process is run in a chroot environment that only contains the subset of the store that the build process depends on, as specified by its derivation (see derivation), plus a set of specific system directories.  By default, the latter contains /dev and /dev/pts.  Furthermore, on GNU/Linux, the build environment is a container: in addition to having its own file system tree, it has a separate mount name space, its own PID name space, network name space, etc.  This helps achieve reproducible builds (see Features).

When the daemon performs a build on behalf of the user, it creates a build directory under /tmp or under the directory specified by its TMPDIR environment variable.  This directory is shared with the container for the duration of the build, though within the container, the build tree is always called /tmp/guix-build-NAME.drv-0.

The build directory is automatically deleted upon completion, unless the build failed and the client specified --keep-failed (see --keep-failed).

The daemon listens for connections and spawns one sub-process for each session started by a client (one of the guix sub-commands).  The guix processes command allows you to get an overview of the activity on your system by viewing each of the active sessions and clients. See Invoking guix processes, for more information.

The following command-line options are supported:

--build-users-group=GROUP
     Take users from GROUP to run build processes (see build users).

--no-substitutes
     Do not use substitutes for build products.  That is, always build things locally instead of allowing downloads of pre-built binaries (see Substitutes).

     When the daemon runs with --no-substitutes, clients can still explicitly enable substitution via the set-build-options remote procedure call (see The Store).

--substitute-urls=URLS
     Consider URLS the default whitespace-separated list of substitute source URLs.  When this option is omitted, https://ci.guix.gnu.org https://bordeaux.guix.gnu.org is used.

     This means that substitutes may be downloaded from URLS, as long as they are signed by a trusted signature (see Substitutes).

     See Getting Substitutes from Other Servers, for more information on how to configure the daemon to get substitutes from other servers.

--no-offload
     Do not use offload builds to other machines (see Daemon Offload Setup).  That is, always build things locally instead of offloading builds to remote machines.

--cache-failures
     Cache build failures.  By default, only successful builds are cached.

     When this option is used, guix gc --list-failures can be used to query the set of store items marked as failed; guix gc --clear-failures removes store items from the set of cached failures. See Invoking guix gc.

--cores=N
-c N
     Use N CPU cores to build each derivation; 0 means as many as available.

     The default value is 0, but it may be overridden by clients, such as the --cores option of guix build (see Invoking guix build).

     The effect is to define the NIX_BUILD_CORES environment variable in the build process, which can then use it to exploit internal parallelism---for instance, by running make -j$NIX_BUILD_CORES.

--max-jobs=N
-M N
     Allow at most N build jobs in parallel.  The default value is 1.  Setting it to 0 means that no builds will be performed locally; instead, the daemon will offload builds (see Daemon Offload Setup), or simply fail.

--max-silent-time=SECONDS
     When the build or substitution process remains silent for more than SECONDS, terminate it and report a build failure.

     The default value is 3600 (one hour).

     The value specified here can be overridden by clients (see --max-silent-time).

--timeout=SECONDS
     Likewise, when the build or substitution process lasts for more than SECONDS, terminate it and report a build failure.

     The default value is 24 hours.

     The value specified here can be overridden by clients (see --timeout).

--rounds=N
     Build each derivation N times in a row, and raise an error if consecutive build results are not bit-for-bit identical.  Note that this setting can be overridden by clients such as guix build (see Invoking guix build).

     When used in conjunction with --keep-failed, the differing output is kept in the store, under /gnu/store/...-check. This makes it easy to look for differences between the two results.

--debug
     Produce debugging output.

     This is useful to debug daemon start-up issues, but then it may be overridden by clients, for example the --verbosity option of guix build (see Invoking guix build).

--chroot-directory=DIR
     Add DIR to the build chroot.

     Doing this may change the result of build processes---for instance if they use optional dependencies found in DIR when it is available, and not otherwise.  For that reason, it is not recommended to do so. Instead, make sure that each derivation declares all the inputs that it needs.

--disable-chroot
     Disable chroot builds.

     Using this option is not recommended since, again, it would allow build processes to gain access to undeclared dependencies.  It is necessary, though, when guix-daemon is running under an unprivileged user account.

--log-compression=TYPE
     Compress build logs according to TYPE, one of gzip, bzip2, or none.

     Unless --lose-logs is used, all the build logs are kept in the LOCALSTATEDIR.  To save space, the daemon automatically compresses them with gzip by default.

--discover[=yes|no]
     Whether to discover substitute servers on the local network using mDNS and DNS-SD.

     This feature is still experimental.  However, here are a few considerations.

      1. It might be faster/less expensive than fetching from remote servers;

      2. There are no security risks, only genuine substitutes will be used (see Substitute Authentication);

      3. An attacker advertising guix publish on your LAN cannot serve you malicious binaries, but they can learn what software you’re installing;

      4. Servers may serve substitute over HTTP, unencrypted, so anyone on the LAN can see what software you’re installing.

     It is also possible to enable or disable substitute server discovery at run-time by running:

          herd discover guix-daemon on
          herd discover guix-daemon off

--disable-deduplication
     Disable automatic file ``deduplication'' in the store.

     By default, files added to the store are automatically ``deduplicated'': if a newly added file is identical to another one found in the store, the daemon makes the new file a hard link to the other file.  This can noticeably reduce disk usage, at the expense of slightly increased input/output load at the end of a build process.  This option disables this optimization.

--gc-keep-outputs[=yes|no]
     Tell whether the garbage collector (GC) must keep outputs of live derivations.

     When set to yes, the GC will keep the outputs of any live derivation available in the store---the .drv files.  The default is no, meaning that derivation outputs are kept only if they are reachable from a GC root.  See Invoking guix gc, for more on GC roots.

--gc-keep-derivations[=yes|no]
     Tell whether the garbage collector (GC) must keep derivations corresponding to live outputs.

     When set to yes, as is the case by default, the GC keeps derivations---i.e., .drv files---as long as at least one of their outputs is live.  This allows users to keep track of the origins of items in their store.  Setting it to no saves a bit of disk space.

     In this way, setting --gc-keep-derivations to yes causes liveness to flow from outputs to derivations, and setting --gc-keep-outputs to yes causes liveness to flow from derivations to outputs.  When both are set to yes, the effect is to keep all the build prerequisites (the sources, compiler, libraries, and other build-time tools) of live objects in the store, regardless of whether these prerequisites are reachable from a GC root.  This is convenient for developers since it saves rebuilds or downloads.

--impersonate-linux-2.6
     On Linux-based systems, impersonate Linux 2.6.  This means that the kernel's uname system call will report 2.6 as the release number.

     This might be helpful to build programs that (usually wrongfully) depend on the kernel version number.

--lose-logs
     Do not keep build logs.  By default they are kept under LOCALSTATEDIR/guix/log.

--system=SYSTEM
     Assume SYSTEM as the current system type.  By default it is the architecture/kernel pair found at configure time, such as x86_64-linux.

--listen=ENDPOINT
     Listen for connections on ENDPOINT.  ENDPOINT is interpreted as the file name of a Unix-domain socket if it starts with / (slash sign).  Otherwise, ENDPOINT is interpreted as a host name or host name and port to listen to.  Here are a few examples:

     --listen=/gnu/var/daemon
          Listen for connections on the /gnu/var/daemon Unix-domain socket, creating it if needed.

     --listen=localhost
          Listen for TCP connections on the network interface corresponding to localhost, on port 44146.

     --listen=128.0.0.42:1234
          Listen for TCP connections on the network interface corresponding to 128.0.0.42, on port 1234.

     This option can be repeated multiple times, in which case guix-daemon accepts connections on all the specified endpoints.  Users can tell client commands what endpoint to connect to by setting the GUIX_DAEMON_SOCKET environment variable (see GUIX_DAEMON_SOCKET).

          The daemon protocol is unauthenticated and unencrypted.  Using --listen=HOST is suitable on local networks, such as clusters, where only trusted nodes may connect to the build daemon.  In other cases where remote access to the daemon is needed, we recommend using Unix-domain sockets along with SSH.

     When --listen is omitted, guix-daemon listens for connections on the Unix-domain socket located at LOCALSTATEDIR/guix/daemon-socket/socket.

Application Setup
=================

When using Guix on top of GNU/Linux distribution other than Guix System---a so-called foreign distro---a few additional steps are needed to get everything in place.  Here are some of them.

Locales
-------

Packages installed via Guix will not use the locale data of the host system.  Instead, you must first install one of the locale packages available with Guix and then define the GUIX_LOCPATH environment variable:

     $ guix install glibc-locales
     $ export GUIX_LOCPATH=$HOME/.guix-profile/lib/locale

Note that the glibc-locales package contains data for all the locales supported by the GNU libc and weighs in at around 930 MiB (The size of the glibc-locales package is reduced down to about 213 MiB with store deduplication and further down to about 67 MiB when using a zstd-compressed Btrfs file system.).  If you only need a few locales, you can define your custom locales package via the make-glibc-utf8-locales procedure from the (gnu packages base) module.  The following example defines a package containing the various Canadian UTF-8 locales known to the GNU libc, that weighs around 14 MiB:

     (use-modules (gnu packages base))

     (define my-glibc-locales
       (make-glibc-utf8-locales
        glibc
        #:locales (list "en_CA" "fr_CA" "ik_CA" "iu_CA" "shs_CA")
        #:name "glibc-canadian-utf8-locales"))

The GUIX_LOCPATH variable plays a role similar to LOCPATH (see LOCPATH (The GNU C Library Reference Manual)).  There are two important differences though:

 1. GUIX_LOCPATH is honored only by the libc in Guix, and not by the libc provided by foreign distros.  Thus, using GUIX_LOCPATH allows you to make sure the programs of the foreign distro will not end up loading incompatible locale data.

 2. libc suffixes each entry of GUIX_LOCPATH with /X.Y, where X.Y is the libc version---e.g., 2.22.  This means that, should your Guix profile contain a mixture of programs linked against different libc version, each libc version will only try to load locale data in the right format.

This is important because the locale data format used by different libc versions may be incompatible.

Name Service Switch
-------------------

When using Guix on a foreign distro, we strongly recommend that the system run the GNU C library's name service cache daemon, nscd, which should be listening on the /var/run/nscd/socket socket.  Failing to do that, applications installed with Guix may fail to look up host names or user accounts, or may even crash.  The next paragraphs explain why.

The GNU C library implements a name service switch (NSS), which is an extensible mechanism for ``name lookups'' in general: host name resolution, user accounts, and more (see Name Service Switch (The GNU C Library Reference Manual)).

Being extensible, the NSS supports plugins, which provide new name lookup implementations: for example, the nss-mdns plugin allow resolution of .local host names, the nis plugin allows user account lookup using the Network information service (NIS), and so on.  These extra ``lookup services'' are configured system-wide in /etc/nsswitch.conf, and all the programs running on the system honor those settings (see NSS Configuration File (The GNU C Reference Manual)).

When they perform a name lookup---for instance by calling the getaddrinfo function in C---applications first try to connect to the nscd; on success, nscd performs name lookups on their behalf.  If the nscd is not running, then they perform the name lookup by themselves, by loading the name lookup services into their own address space and running it.  These name lookup services---the libnss_*.so files---are dlopen'd, but they may come from the host system's C library, rather than from the C library the application is linked against (the C library coming from Guix).

And this is where the problem is: if your application is linked against Guix's C library (say, glibc 2.24) and tries to load NSS plugins from another C library (say, libnss_mdns.so for glibc 2.22), it will likely crash or have its name lookups fail unexpectedly.

Running nscd on the system, among other advantages, eliminates this binary incompatibility problem because those libnss_*.so files are loaded in the nscd process, not in applications themselves.

X11 Fonts
---------

The majority of graphical applications use Fontconfig to locate and load fonts and perform X11-client-side rendering.  The fontconfig package in Guix looks for fonts in $HOME/.guix-profile by default.  Thus, to allow graphical applications installed with Guix to display fonts, you have to install fonts with Guix as well.  Essential font packages include font-ghostscript, font-dejavu, and font-gnu-freefont.

Once you have installed or removed fonts, or when you notice an application that does not find fonts, you may need to install Fontconfig and to force an update of its font cache by running:

     guix install fontconfig
     fc-cache -rv

To display text written in Chinese languages, Japanese, or Korean in graphical applications, consider installing font-adobe-source-han-sans or font-wqy-zenhei.  The former has multiple outputs, one per language family (see Packages with Multiple Outputs).  For instance, the following command installs fonts for Chinese languages:

     guix install font-adobe-source-han-sans:cn

Older programs such as xterm do not use Fontconfig and instead rely on server-side font rendering.  Such programs require to specify a full name of a font using XLFD (X Logical Font Description), like this:

     -*-dejavu sans-medium-r-normal-*-*-100-*-*-*-*-*-1

To be able to use such full names for the TrueType fonts installed in your Guix profile, you need to extend the font path of the X server:

     xset +fp $(dirname $(readlink -f ~/.guix-profile/share/fonts/truetype/fonts.dir))

After that, you can run xlsfonts (from xlsfonts package) to make sure your TrueType fonts are listed there.

X.509 Certificates
------------------

The nss-certs package provides X.509 certificates, which allow programs to authenticate Web servers accessed over HTTPS.

When using Guix on a foreign distro, you can install this package and define the relevant environment variables so that packages know where to look for certificates.  See X.509 Certificates, for detailed information.

Emacs Packages
--------------

When you install Emacs packages with Guix, the Elisp files are placed under the share/emacs/site-lisp/ directory of the profile in which they are installed.  The Elisp libraries are made available to Emacs through the EMACSLOADPATH environment variable, which is set when installing Emacs itself.

Additionally, autoload definitions are automatically evaluated at the initialization of Emacs, by the Guix-specific guix-emacs-autoload-packages procedure.  This procedure can be interactively invoked to have newly installed Emacs packages discovered, without having to restart Emacs.  If, for some reason, you want to avoid auto-loading the Emacs packages installed with Guix, you can do so by running Emacs with the --no-site-file option (see Init File (The GNU Emacs Manual)).

     Emacs can now compile packages natively.  Under the default configuration, this means that Emacs packages will now be just-in-time (JIT) compiled as you use them, and the results stored in a subdirectory of your user-emacs-directory.

     Furthermore, the build system for Emacs packages transparently supports native compilation, but note, that emacs-minimal---the default Emacs for building packages---has been configured without native compilation. To natively compile your emacs packages ahead of time, use a transformation like --with-input=emacs-minimal=emacs.

Upgrading Guix
==============

To upgrade Guix, run:

     guix pull

See Invoking guix pull, for more information.

On a foreign distro, you can upgrade the build daemon by running:

     sudo -i guix pull

followed by (assuming your distro uses the systemd service management tool):

     systemctl restart guix-daemon.service

On Guix System, upgrading the daemon is achieved by reconfiguring the system (see guix system reconfigure).

System Installation
*******************

This section explains how to install Guix System on a machine.  Guix, as a package manager, can also be installed on top of a running GNU/Linux system, see Installation.

     You are reading this documentation with an Info reader.  For details on how to use it, hit the RET key (``return'' or ``enter'') on the link that follows: see Info reader (Stand-alone GNU Info).  Hit l afterwards to come back here.

     Alternatively, run info info in another tty to keep the manual available.

Limitations
===========

We consider Guix System to be ready for a wide range of ``desktop'' and server use cases.  The reliability guarantees it provides---transactional upgrades and rollbacks, reproducibility---make it a solid foundation.

Nevertheless, before you proceed with the installation, be aware of the following noteworthy limitations applicable to version VERSION:

  * More and more system services are provided (see Services), but some may be missing.

  * GNOME, Xfce, LXDE, and Enlightenment are available (see Desktop Services), as well as a number of X11 window managers.  However, KDE is currently missing.

More than a disclaimer, this is an invitation to report issues (and success stories!), and to join us in improving it.  See Contributing, for more info.

Hardware Considerations
=======================

GNU Guix focuses on respecting the user's computing freedom.  It builds around the kernel Linux-libre, which means that only hardware for which free software drivers and firmware exist is supported.  Nowadays, a wide range of off-the-shelf hardware is supported on GNU/Linux-libre---from keyboards to graphics cards to scanners and Ethernet controllers.  Unfortunately, there are still areas where hardware vendors deny users control over their own computing, and such hardware is not supported on Guix System.

One of the main areas where free drivers or firmware are lacking is WiFi devices.  WiFi devices known to work include those using Atheros chips (AR9271 and AR7010), which corresponds to the ath9k Linux-libre driver, and those using Broadcom/AirForce chips (BCM43xx with Wireless-Core Revision 5), which corresponds to the b43-open Linux-libre driver.  Free firmware exists for both and is available out-of-the-box on Guix System, as part of %base-firmware (see firmware).

The installer warns you early on if it detects devices that are known not to work due to the lack of free firmware or free drivers.

The Free Software Foundation (https://www.fsf.org/) runs Respects Your Freedom (https://www.fsf.org/ryf) (RYF), a certification program for hardware products that respect your freedom and your privacy and ensure that you have control over your device.  We encourage you to check the list of RYF-certified devices.

Another useful resource is the H-Node (https://www.h-node.org/) web site.  It contains a catalog of hardware devices with information about their support in GNU/Linux.

USB Stick and DVD Installation
==============================

An ISO-9660 installation image that can be written to a USB stick or burnt to a DVD can be downloaded from https://ftp.gnu.org/gnu/guix/guix-system-install-VERSION.x86_64-linux.iso, where you can replace x86_64-linux with one of:

x86_64-linux
     for a GNU/Linux system on Intel/AMD-compatible 64-bit CPUs;

i686-linux
     for a 32-bit GNU/Linux system on Intel-compatible CPUs.

Make sure to download the associated .sig file and to verify the authenticity of the image against it, along these lines:

     $ wget https://ftp.gnu.org/gnu/guix/guix-system-install-VERSION.x86_64-linux.iso.sig
     $ gpg --verify guix-system-install-VERSION.x86_64-linux.iso.sig

If that command fails because you do not have the required public key, then run this command to import it:

     $ wget https://sv.gnu.org/people/viewgpg.php?user_id=15145 \
           -qO - | gpg --import -

and rerun the gpg --verify command.

Take note that a warning like ``This key is not certified with a trusted signature!'' is normal.

This image contains the tools necessary for an installation. It is meant to be copied as is to a large-enough USB stick or DVD.

Copying to a USB Stick
----------------------

Insert a USB stick of 1 GiB or more into your machine, and determine its device name.  Assuming that the USB stick is known as /dev/sdX, copy the image with:

     dd if=guix-system-install-VERSION.x86_64-linux.iso of=/dev/sdX status=progress
     sync

Access to /dev/sdX usually requires root privileges.

Burning on a DVD
----------------

Insert a blank DVD into your machine, and determine its device name.  Assuming that the DVD drive is known as /dev/srX, copy the image with:

     growisofs -dvd-compat -Z /dev/srX=guix-system-install-VERSION.x86_64-linux.iso

Access to /dev/srX usually requires root privileges.

Booting
-------

Once this is done, you should be able to reboot the system and boot from the USB stick or DVD.  The latter usually requires you to get in the BIOS or UEFI boot menu, where you can choose to boot from the USB stick. In order to boot from Libreboot, switch to the command mode by pressing the c key and type search_grub usb.

Sadly, on some machines, the installation medium cannot be properly booted and you only see a black screen after booting even after you waited for ten minutes.  This may indicate that your machine cannot run Guix System; perhaps you instead want to install Guix on a foreign distro (see Binary Installation).  But don't give up just yet; a possible workaround is pressing the e key in the GRUB boot menu and appending nomodeset to the Linux bootline. Sometimes the black screen issue can also be resolved by connecting a different display.

See Installing Guix in a VM, if, instead, you would like to install Guix System in a virtual machine (VM).

Preparing for Installation
==========================

Once you have booted, you can use the guided graphical installer, which makes it easy to get started (see Guided Graphical Installation).  Alternatively, if you are already familiar with GNU/Linux and if you want more control than what the graphical installer provides, you can choose the ``manual'' installation process (see Manual Installation).

The graphical installer is available on TTY1.  You can obtain root shells on TTYs 3 to 6 by hitting ctrl-alt-f3, ctrl-alt-f4, etc.  TTY2 shows this documentation and you can reach it with ctrl-alt-f2.  Documentation is browsable using the Info reader commands (see Stand-alone GNU Info).  The installation system runs the GPM mouse daemon, which allows you to select text with the left mouse button and to paste it with the middle button.

     Installation requires access to the Internet so that any missing dependencies of your system configuration can be downloaded.  See the ``Networking'' section below.

Guided Graphical Installation
=============================

The graphical installer is a text-based user interface.  It will guide you, with dialog boxes, through the steps needed to install GNU Guix System.

The first dialog boxes allow you to set up the system as you use it during the installation: you can choose the language, keyboard layout, and set up networking, which will be used during the installation.  The image below shows the networking dialog.

networking setup with the graphical installer

Later steps allow you to partition your hard disk, as shown in the image below, to choose whether or not to use encrypted file systems, to enter the host name and root password, and to create an additional account, among other things.

partitioning with the graphical installer

Note that, at any time, the installer allows you to exit the current installation step and resume at a previous step, as show in the image below.

resuming the installation process

Once you're done, the installer produces an operating system configuration and displays it (see Using the Configuration System).  At that point you can hit ``OK'' and installation will proceed.  On success, you can reboot into the new system and enjoy.  See After System Installation, for what's next!

Manual Installation
===================

This section describes how you would ``manually'' install GNU Guix System on your machine.  This option requires familiarity with GNU/Linux, with the shell, and with common administration tools.  If you think this is not for you, consider using the guided graphical installer (see Guided Graphical Installation).

The installation system provides root shells on TTYs 3 to 6; press ctrl-alt-f3, ctrl-alt-f4, and so on to reach them.  It includes many common tools needed to install the system, but is also a full-blown Guix System.  This means that you can install additional packages, should you need it, using guix package (see Invoking guix package).

Keyboard Layout, Networking, and Partitioning
---------------------------------------------

Before you can install the system, you may want to adjust the keyboard layout, set up networking, and partition your target hard disk.  This section will guide you through this.

Keyboard Layout
...............

The installation image uses the US qwerty keyboard layout.  If you want to change it, you can use the loadkeys command.  For example, the following command selects the Dvorak keyboard layout:

     loadkeys dvorak

See the files under /run/current-system/profile/share/keymaps for a list of available keyboard layouts.  Run man loadkeys for more information.

Networking
..........

Run the following command to see what your network interfaces are called:

     ifconfig -a

... or, using the GNU/Linux-specific ip command:

     ip address

Wired interfaces have a name starting with e; for example, the interface corresponding to the first on-board Ethernet controller is called eno1.  Wireless interfaces have a name starting with w, like w1p2s0.

Wired connection
     To configure a wired network run the following command, substituting INTERFACE with the name of the wired interface you want to use.

          ifconfig INTERFACE up

     ... or, using the GNU/Linux-specific ip command:

          ip link set INTERFACE up

Wireless connection
     To configure wireless networking, you can create a configuration file for the wpa_supplicant configuration tool (its location is not important) using one of the available text editors such as nano:

          nano wpa_supplicant.conf

     As an example, the following stanza can go to this file and will work for many wireless networks, provided you give the actual SSID and passphrase for the network you are connecting to:

          network={
            ssid="MY-SSID"
            key_mgmt=WPA-PSK
            psk="the network's secret passphrase"
          }

     Start the wireless service and run it in the background with the following command (substitute INTERFACE with the name of the network interface you want to use):

          wpa_supplicant -c wpa_supplicant.conf -i INTERFACE -B

     Run man wpa_supplicant for more information.

At this point, you need to acquire an IP address.  On a network where IP addresses are automatically assigned via DHCP, you can run:

     dhclient -v INTERFACE

Try to ping a server to see if networking is up and running:

     ping -c 3 gnu.org

Setting up network access is almost always a requirement because the image does not contain all the software and tools that may be needed.

If you need HTTP and HTTPS access to go through a proxy, run the following command:

     herd set-http-proxy guix-daemon URL

where URL is the proxy URL, for example http://example.org:8118.

If you want to, you can continue the installation remotely by starting an SSH server:

     herd start ssh-daemon

Make sure to either set a password with passwd, or configure OpenSSH public key authentication before logging in.

Disk Partitioning
.................

Unless this has already been done, the next step is to partition, and then format the target partition(s).

The installation image includes several partitioning tools, including Parted (see Overview (GNU Parted User Manual)), fdisk, and cfdisk.  Run it and set up your disk with the partition layout you want:

     cfdisk

If your disk uses the GUID Partition Table (GPT) format and you plan to install BIOS-based GRUB (which is the default), make sure a BIOS Boot Partition is available (see BIOS installation (GNU GRUB manual)).

If you instead wish to use EFI-based GRUB, a FAT32 EFI System Partition (ESP) is required.  This partition can be mounted at /boot/efi for instance and must have the esp flag set.  E.g., for parted:

     parted /dev/sda set 1 esp on

     Unsure whether to use EFI- or BIOS-based GRUB?  If the directory /sys/firmware/efi exists in the installation image, then you should probably perform an EFI installation, using grub-efi-bootloader. Otherwise you should use the BIOS-based GRUB, known as grub-bootloader.  See Bootloader Configuration, for more info on bootloaders.

Once you are done partitioning the target hard disk drive, you have to create a file system on the relevant partition(s) (Currently Guix System only supports ext4, btrfs, JFS, F2FS, and XFS file systems.  In particular, code that reads file system UUIDs and labels only works for these file system types.).  For the ESP, if you have one and assuming it is /dev/sda1, run:

     mkfs.fat -F32 /dev/sda1

For the root file system, ext4 is the most widely used format.  Other file systems, such as Btrfs, support compression, which is reported to nicely complement file deduplication that the daemon performs independently of the file system (see deduplication).

Preferably, assign file systems a label so that you can easily and reliably refer to them in file-system declarations (see File Systems).  This is typically done using the -L option of mkfs.ext4 and related commands.  So, assuming the target root partition lives at /dev/sda2, a file system with the label my-root can be created with:

     mkfs.ext4 -L my-root /dev/sda2

If you are instead planning to encrypt the root partition, you can use the Cryptsetup/LUKS utilities to do that (see man cryptsetup for more information).

     Note that GRUB can unlock LUKS2 devices since version 2.06, but only supports the PBKDF2 key derivation function, which is not the default for cryptsetup luksFormat.  You can check which key derivation function is being used by a device by running cryptsetup luksDump DEVICE, and looking for the PBKDF field of your keyslots.

Assuming you want to store the root partition on /dev/sda2, the command sequence to format it as a LUKS2 partition would be along these lines:

     cryptsetup luksFormat --type luks2 --pbkdf pbkdf2 /dev/sda2
     cryptsetup open /dev/sda2 my-partition
     mkfs.ext4 -L my-root /dev/mapper/my-partition

Once that is done, mount the target file system under /mnt with a command like (again, assuming my-root is the label of the root file system):

     mount LABEL=my-root /mnt

Also mount any other file systems you would like to use on the target system relative to this path.  If you have opted for /boot/efi as an EFI mount point for example, mount it at /mnt/boot/efi now so it is found by guix system init afterwards.

Finally, if you plan to use one or more swap partitions (see Swap Space), make sure to initialize them with mkswap.  Assuming you have one swap partition on /dev/sda3, you would run:

     mkswap /dev/sda3
     swapon /dev/sda3

Alternatively, you may use a swap file.  For example, assuming that in the new system you want to use the file /swapfile as a swap file, you would run (This example will work for many types of file systems (e.g., ext4).  However, for copy-on-write file systems (e.g., btrfs), the required steps may be different.  For details, see the manual pages for mkswap and swapon.):

     # This is 10 GiB of swap space.  Adjust "count" to change the size.
     dd if=/dev/zero of=/mnt/swapfile bs=1MiB count=10240
     # For security, make the file readable and writable only by root.
     chmod 600 /mnt/swapfile
     mkswap /mnt/swapfile
     swapon /mnt/swapfile

Note that if you have encrypted the root partition and created a swap file in its file system as described above, then the encryption also protects the swap file, just like any other file in that file system.

Proceeding with the Installation
--------------------------------

With the target partitions ready and the target root mounted on /mnt, we're ready to go.  First, run:

     herd start cow-store /mnt

This makes /gnu/store copy-on-write, such that packages added to it during the installation phase are written to the target disk on /mnt rather than kept in memory.  This is necessary because the first phase of the guix system init command (see below) entails downloads or builds to /gnu/store which, initially, is an in-memory file system.

Next, you have to edit a file and provide the declaration of the operating system to be installed.  To that end, the installation system comes with three text editors.  We recommend GNU nano (see GNU nano Manual), which supports syntax highlighting and parentheses matching; other editors include mg (an Emacs clone), and nvi (a clone of the original BSD vi editor). We strongly recommend storing that file on the target root file system, say, as /mnt/etc/config.scm.  Failing to do that, you will have lost your configuration file once you have rebooted into the newly-installed system.

See Using the Configuration System, for an overview of the configuration file.  The example configurations discussed in that section are available under /etc/configuration in the installation image.  Thus, to get started with a system configuration providing a graphical display server (a ``desktop'' system), you can run something along these lines:

     # mkdir /mnt/etc
     # cp /etc/configuration/desktop.scm /mnt/etc/config.scm
     # nano /mnt/etc/config.scm

You should pay attention to what your configuration file contains, and in particular:

  * Make sure the bootloader-configuration form refers to the targets you want to install GRUB on.  It should mention grub-bootloader if you are installing GRUB in the legacy way, or grub-efi-bootloader for newer UEFI systems.  For legacy systems, the targets field contain the names of the devices, like (list "/dev/sda"); for UEFI systems it names the paths to mounted EFI partitions, like (list "/boot/efi"); do make sure the paths are currently mounted and a file-system entry is specified in your configuration.

  * Be sure that your file system labels match the value of their respective device fields in your file-system configuration, assuming your file-system configuration uses the file-system-label procedure in its device field.

  * If there are encrypted or RAID partitions, make sure to add a mapped-devices field to describe them (see Mapped Devices).

Once you are done preparing the configuration file, the new system must be initialized (remember that the target root file system is mounted under /mnt):

     guix system init /mnt/etc/config.scm /mnt

This copies all the necessary files and installs GRUB on /dev/sdX, unless you pass the --no-bootloader option.  For more information, see Invoking guix system.  This command may trigger downloads or builds of missing packages, which can take some time.

Once that command has completed---and hopefully succeeded!---you can run reboot and boot into the new system.  The root password in the new system is initially empty; other users' passwords need to be initialized by running the passwd command as root, unless your configuration specifies otherwise (see user account passwords). See After System Installation, for what's next!

After System Installation
=========================

Success, you've now booted into Guix System!  From then on, you can update the system whenever you want by running, say:

     guix pull
     sudo guix system reconfigure /etc/config.scm

This builds a new system generation with the latest packages and services (see Invoking guix system).  We recommend doing that regularly so that your system includes the latest security updates (see Security Updates).

     Note that sudo guix runs your user's guix command and not root's, because sudo leaves PATH unchanged.  To explicitly run root's guix, type sudo -i guix ....

     The difference matters here, because guix pull updates the guix command and package definitions only for the user it is run as.  This means that if you choose to use guix system reconfigure in root's login shell, you'll need to guix pull separately.

Now, see Getting Started, and join us on #guix on the Libera Chat IRC network or on guix-devel@gnu.org to share your experience!

Installing Guix in a Virtual Machine
====================================

If you'd like to install Guix System in a virtual machine (VM) or on a virtual private server (VPS) rather than on your beloved machine, this section is for you.

To boot a QEMU (https://qemu.org/) VM for installing Guix System in a disk image, follow these steps:

 1. First, retrieve and decompress the Guix system installation image as described previously (see USB Stick and DVD Installation).

 2. Create a disk image that will hold the installed system.  To make a qcow2-formatted disk image, use the qemu-img command:

          qemu-img create -f qcow2 guix-system.img 50G

     The resulting file will be much smaller than 50 GB (typically less than 1 MB), but it will grow as the virtualized storage device is filled up.

 3. Boot the USB installation image in an VM:

          qemu-system-x86_64 -m 1024 -smp 1 -enable-kvm \
            -nic user,model=virtio-net-pci -boot menu=on,order=d \
            -drive file=guix-system.img \
            -drive media=cdrom,readonly=on,file=guix-system-install-VERSION.SYSTEM.iso

     -enable-kvm is optional, but significantly improves performance, see Running Guix in a VM.

 4. You're now root in the VM, proceed with the installation process. See Preparing for Installation, and follow the instructions.

Once installation is complete, you can boot the system that's on your guix-system.img image.  See Running Guix in a VM, for how to do that.

Building the Installation Image
===============================

The installation image described above was built using the guix system command, specifically:

     guix system image -t iso9660 gnu/system/install.scm

Have a look at gnu/system/install.scm in the source tree, and see also Invoking guix system for more information about the installation image.

Building the Installation Image for ARM Boards
==============================================

Many ARM boards require a specific variant of the U-Boot (https://www.denx.de/wiki/U-Boot/) bootloader.

If you build a disk image and the bootloader is not available otherwise (on another boot drive etc), it's advisable to build an image that includes the bootloader, specifically:

     guix system image --system=armhf-linux -e '((@ (gnu system install) os-with-u-boot) (@ (gnu system install) installation-os) "A20-OLinuXino-Lime2")'

A20-OLinuXino-Lime2 is the name of the board.  If you specify an invalid board, a list of possible boards will be printed.

Getting Started
***************

Presumably, you've reached this section because either you have installed Guix on top of another distribution (see Installation), or you've installed the standalone Guix System (see System Installation).  It's time for you to get started using Guix and this section aims to help you do that and give you a feel of what it's like.

Guix is about installing software, so probably the first thing you'll want to do is to actually look for software.  Let's say you're looking for a text editor, you can run:

     guix search text editor

This command shows you a number of matching packages, each time showing the package's name, version, a description, and additional info. Once you've found out the one you want to use, let's say Emacs (ah ha!), you can go ahead and install it (run this command as a regular user, no need for root privileges!):

     guix install emacs

You've installed your first package, congrats!  The package is now visible in your default profile, $HOME/.guix-profile---a profile is a directory containing installed packages. In the process, you've probably noticed that Guix downloaded pre-built binaries; or, if you explicitly chose to not use pre-built binaries, then probably Guix is still building software (see Substitutes, for more info).

Unless you're using Guix System, the guix install command must have printed this hint:

     hint: Consider setting the necessary environment variables by running:

          GUIX_PROFILE="$HOME/.guix-profile"
          . "$GUIX_PROFILE/etc/profile"

     Alternately, see `guix package --search-paths -p "$HOME/.guix-profile"'.

Indeed, you must now tell your shell where emacs and other programs installed with Guix are to be found.  Pasting the two lines above will do just that: it will add $HOME/.guix-profile/bin---which is where the installed package is---to the PATH environment variable.  You can paste these two lines in your shell so they take effect right away, but more importantly you should add them to ~/.bash_profile (or equivalent file if you do not use Bash) so that environment variables are set next time you spawn a shell.  You only need to do this once and other search paths environment variables will be taken care of similarly---e.g., if you eventually install python and Python libraries, GUIX_PYTHONPATH will be defined.

You can go on installing packages at your will.  To list installed packages, run:

     guix package --list-installed

To remove a package, you would unsurprisingly run guix remove. A distinguishing feature is the ability to roll back any operation you made---installation, removal, upgrade---by simply typing:

     guix package --roll-back

This is because each operation is in fact a transaction that creates a new generation.  These generations and the difference between them can be displayed by running:

     guix package --list-generations

Now you know the basics of package management!

     See Package Management, for more about package management.  You may like declarative package management with guix package --manifest, managing separate profiles with --profile, deleting old generations, collecting garbage, and other nifty features that will come in handy as you become more familiar with Guix.  If you are a developer, see Development for additional tools.  And if you're curious, see Features, to peek under the hood.

     You can also manage the configuration of your entire home environment---your user ``dot files'', services, and packages---using Guix Home.  See Home Configuration, to learn more about it!

Once you've installed a set of packages, you will want to periodically upgrade them to the latest and greatest version.  To do that, you will first pull the latest revision of Guix and its package collection:

     guix pull

The end result is a new guix command, under ~/.config/guix/current/bin.  Unless you're on Guix System, the first time you run guix pull, be sure to follow the hint that the command prints and, similar to what we saw above, paste these two lines in your terminal and .bash_profile:

     GUIX_PROFILE="$HOME/.config/guix/current"
     . "$GUIX_PROFILE/etc/profile"

You must also instruct your shell to point to this new guix:

     hash guix

At this point, you're running a brand new Guix.  You can thus go ahead and actually upgrade all the packages you previously installed:

     guix upgrade

As you run this command, you will see that binaries are downloaded (or perhaps some packages are built), and eventually you end up with the upgraded packages.  Should one of these upgraded packages not be to your liking, remember you can always roll back!

You can display the exact revision of Guix you're currently using by running:

     guix describe

The information it displays is all it takes to reproduce the exact same Guix, be it at a different point in time or on a different machine.

     See Invoking guix pull, for more information.  See Channels, on how to specify additional channels to pull packages from, how to replicate Guix, and more.  You may also find time-machine handy (see Invoking guix time-machine).

If you installed Guix System, one of the first things you'll want to do is to upgrade your system.  Once you've run guix pull to get the latest Guix, you can upgrade the system like this:

     sudo guix system reconfigure /etc/config.scm

Upon completion, the system runs the latest versions of its software packages.  When you eventually reboot, you'll notice a sub-menu in the bootloader that reads ``Old system generations'': it's what allows you to boot an older generation of your system, should the latest generation be ``broken'' or otherwise unsatisfying.  Just like for packages, you can always roll back to a previous generation of the whole system:

     sudo guix system roll-back

There are many things you'll probably want to tweak on your system: adding new user accounts, adding new system services, fiddling with the configuration of those services, etc.  The system configuration is entirely described in the /etc/config.scm file. See Using the Configuration System, to learn how to change it.

Now you know enough to get started!

     The rest of this manual provides a reference for all things Guix.  Here are some additional resources you may find useful:

       * See The GNU Guix Cookbook, for a list of ``how-to'' style of recipes for a variety of applications.

       * The GNU Guix Reference Card (https://guix.gnu.org/guix-refcard.pdf) lists in two pages most of the commands and options you'll ever need.

       * The web site contains instructional videos (https://guix.gnu.org/en/videos/) covering topics such as everyday use of Guix, how to get help, and how to become a contributor.

       * See Documentation, to learn how to access documentation on your computer.

     We hope you will enjoy Guix as much as the community enjoys building it!

Package Management
******************

The purpose of GNU Guix is to allow users to easily install, upgrade, and remove software packages, without having to know about their build procedures or dependencies.  Guix also goes beyond this obvious set of features.

This chapter describes the main features of Guix, as well as the package management tools it provides.  Along with the command-line interface described below (see guix package), you may also use the Emacs-Guix interface (see The Emacs-Guix Reference Manual), after installing emacs-guix package (run M-x guix-help command to start with it):

     guix install emacs-guix

Features
========

Here we assume you've already made your first steps with Guix (see Getting Started) and would like to get an overview about what's going on under the hood.

When using Guix, each package ends up in the package store, in its own directory---something that resembles /gnu/store/xxx-package-1.2, where xxx is a base32 string.

Instead of referring to these directories, users have their own profile, which points to the packages that they actually want to use.  These profiles are stored within each user's home directory, at $HOME/.guix-profile.

For example, alice installs GCC 4.7.2.  As a result, /home/alice/.guix-profile/bin/gcc points to /gnu/store/...-gcc-4.7.2/bin/gcc.  Now, on the same machine, bob had already installed GCC 4.8.0.  The profile of bob simply continues to point to /gnu/store/...-gcc-4.8.0/bin/gcc---i.e., both versions of GCC coexist on the same system without any interference.

The guix package command is the central tool to manage packages (see Invoking guix package).  It operates on the per-user profiles, and can be used with normal user privileges.

The command provides the obvious install, remove, and upgrade operations.  Each invocation is actually a transaction: either the specified operation succeeds, or nothing happens.  Thus, if the guix package process is terminated during the transaction, or if a power outage occurs during the transaction, then the user's profile remains in its previous state, and remains usable.

In addition, any package transaction may be rolled back.  So, if, for example, an upgrade installs a new version of a package that turns out to have a serious bug, users may roll back to the previous instance of their profile, which was known to work well.  Similarly, the global system configuration on Guix is subject to transactional upgrades and roll-back (see Using the Configuration System).

All packages in the package store may be garbage-collected. Guix can determine which packages are still referenced by user profiles, and remove those that are provably no longer referenced (see Invoking guix gc).  Users may also explicitly remove old generations of their profile so that the packages they refer to can be collected.

Guix takes a purely functional approach to package management, as described in the introduction (see Introduction). Each /gnu/store package directory name contains a hash of all the inputs that were used to build that package---compiler, libraries, build scripts, etc.  This direct correspondence allows users to make sure a given package installation matches the current state of their distribution.  It also helps maximize build reproducibility: thanks to the isolated build environments that are used, a given build is likely to yield bit-identical files when performed on different machines (see container).

This foundation allows Guix to support transparent binary/source deployment.  When a pre-built binary for a /gnu/store item is available from an external source---a substitute, Guix just downloads it and unpacks it; otherwise, it builds the package from source, locally (see Substitutes).  Because build results are usually bit-for-bit reproducible, users do not have to trust servers that provide substitutes: they can force a local build and challenge providers (see Invoking guix challenge).

Control over the build environment is a feature that is also useful for developers.  The guix shell command allows developers of a package to quickly set up the right development environment for their package, without having to manually install the dependencies of the package into their profile (see Invoking guix shell).

All of Guix and its package definitions is version-controlled, and guix pull allows you to ``travel in time'' on the history of Guix itself (see Invoking guix pull).  This makes it possible to replicate a Guix instance on a different machine or at a later point in time, which in turn allows you to replicate complete software environments, while retaining precise provenance tracking of the software.

Invoking guix package
=====================

The guix package command is the tool that allows users to install, upgrade, and remove packages, as well as rolling back to previous configurations.  These operations work on a user profile---a directory of installed packages.  Each user has a default profile in $HOME/.guix-profile. The command operates only on the user's own profile, and works with normal user privileges (see Features).  Its syntax is:

     guix package OPTIONS

Primarily, OPTIONS specifies the operations to be performed during the transaction.  Upon completion, a new profile is created, but previous generations of the profile remain available, should the user want to roll back.

For example, to remove lua and install guile and guile-cairo in a single transaction:

     guix package -r lua -i guile guile-cairo

For your convenience, we also provide the following aliases:

  * guix search is an alias for guix package -s,

  * guix install is an alias for guix package -i,

  * guix remove is an alias for guix package -r,

  * guix upgrade is an alias for guix package -u,

  * and guix show is an alias for guix package --show=.

These aliases are less expressive than guix package and provide fewer options, so in some cases you'll probably want to use guix package directly.

guix package also supports a declarative approach whereby the user specifies the exact set of packages to be available and passes it via the --manifest option (see --manifest).

For each user, a symlink to the user's default profile is automatically created in $HOME/.guix-profile.  This symlink always points to the current generation of the user's default profile.  Thus, users can add $HOME/.guix-profile/bin to their PATH environment variable, and so on. If you are not using Guix System, consider adding the following lines to your ~/.bash_profile (see Bash Startup Files (The GNU Bash Reference Manual)) so that newly-spawned shells get all the right environment variable definitions:

     GUIX_PROFILE="$HOME/.guix-profile" ; \
     source "$GUIX_PROFILE/etc/profile"

In a multi-user setup, user profiles are stored in a place registered as a garbage-collector root, which $HOME/.guix-profile points to (see Invoking guix gc).  That directory is normally LOCALSTATEDIR/guix/profiles/per-user/USER, where LOCALSTATEDIR is the value passed to configure as --localstatedir, and USER is the user name.  The per-user directory is created when guix-daemon is started, and the USER sub-directory is created by guix package.

The OPTIONS can be among the following:

--install=PACKAGE ...
-i PACKAGE ...
     Install the specified PACKAGEs.

     Each PACKAGE may specify a simple package name, such as guile, optionally followed by an at-sign and version number, such as guile@3.0.7 or simply guile@3.0.  In the latter case, the newest version prefixed by 3.0 is selected.

     If no version number is specified, the newest available version will be selected.  In addition, such a PACKAGE specification may contain a colon, followed by the name of one of the outputs of the package, as in gcc:doc or binutils@2.22:lib (see Packages with Multiple Outputs).

     Packages with a corresponding name (and optionally version) are searched for among the GNU distribution modules (see Package Modules).

     Alternatively, a PACKAGE can directly specify a store file name such as /gnu/store/...-guile-3.0.7, as produced by, e.g., guix build.

     Sometimes packages have propagated inputs: these are dependencies that automatically get installed along with the required package (see propagated-inputs in package objects, for information about propagated inputs in package definitions).

     An example is the GNU MPC library: its C header files refer to those of the GNU MPFR library, which in turn refer to those of the GMP library. Thus, when installing MPC, the MPFR and GMP libraries also get installed in the profile; removing MPC also removes MPFR and GMP---unless they had also been explicitly installed by the user.

     Besides, packages sometimes rely on the definition of environment variables for their search paths (see explanation of --search-paths below).  Any missing or possibly incorrect environment variable definitions are reported here.

--install-from-expression=EXP
-e EXP
     Install the package EXP evaluates to.

     EXP must be a Scheme expression that evaluates to a <package> object.  This option is notably useful to disambiguate between same-named variants of a package, with expressions such as (@ (gnu packages base) guile-final).

     Note that this option installs the first output of the specified package, which may be insufficient when needing a specific output of a multiple-output package.

--install-from-file=FILE
-f FILE
     Install the package that the code within FILE evaluates to.

     As an example, FILE might contain a definition like this (see Defining Packages):

               [file package-hello.scm not included]

     Developers may find it useful to include such a guix.scm file in the root of their project source tree that can be used to test development snapshots and create reproducible development environments (see Invoking guix shell).

     The FILE may also contain a JSON representation of one or more package definitions.  Running guix package -f on hello.json with the following contents would result in installing the package greeter after building myhello:

               [file package-hello.json not included]

--remove=PACKAGE ...
-r PACKAGE ...
     Remove the specified PACKAGEs.

     As for --install, each PACKAGE may specify a version number and/or output name in addition to the package name.  For instance, -r glibc:debug would remove the debug output of glibc.

--upgrade[=REGEXP ...]
-u [REGEXP ...]
     Upgrade all the installed packages.  If one or more REGEXPs are specified, upgrade only installed packages whose name matches a REGEXP.  Also see the --do-not-upgrade option below.

     Note that this upgrades package to the latest version of packages found in the distribution currently installed.  To update your distribution, you should regularly run guix pull (see Invoking guix pull).

     When upgrading, package transformations that were originally applied when creating the profile are automatically re-applied (see Package Transformation Options).  For example, assume you first installed Emacs from the tip of its development branch with:

          guix install emacs-next --with-branch=emacs-next=master

     Next time you run guix upgrade, Guix will again pull the tip of the Emacs development branch and build emacs-next from that checkout.

     Note that transformation options such as --with-branch and --with-source depend on external state; it is up to you to ensure that they work as expected.  You can also discard a transformations that apply to a package by running:

          guix install PACKAGE

--do-not-upgrade[=REGEXP ...]
     When used together with the --upgrade option, do not upgrade any packages whose name matches a REGEXP.  For example, to upgrade all packages in the current profile except those containing the substring ``emacs'':

          $ guix package --upgrade . --do-not-upgrade emacs

--manifest=FILE
-m FILE
     Create a new generation of the profile from the manifest object returned by the Scheme code in FILE.  This option can be repeated several times, in which case the manifests are concatenated.

     This allows you to declare the profile's contents rather than constructing it through a sequence of --install and similar commands.  The advantage is that FILE can be put under version control, copied to different machines to reproduce the same profile, and so on.

     FILE must return a manifest object, which is roughly a list of packages:

          (use-package-modules guile emacs)

          (packages->manifest
           (list emacs
                 guile-2.0
                 ;; Use a specific package output.
                 (list guile-2.0 "debug")))

     See Writing Manifests, for information on how to write a manifest. See --export-manifest, to learn how to obtain a manifest file from an existing profile.

--roll-back
     Roll back to the previous generation of the profile---i.e., undo the last transaction.

     When combined with options such as --install, roll back occurs before any other actions.

     When rolling back from the first generation that actually contains installed packages, the profile is made to point to the zeroth generation, which contains no files apart from its own metadata.

     After having rolled back, installing, removing, or upgrading packages overwrites previous future generations.  Thus, the history of the generations in a profile is always linear.

--switch-generation=PATTERN
-S PATTERN
     Switch to a particular generation defined by PATTERN.

     PATTERN may be either a generation number or a number prefixed with ``+'' or ``-''.  The latter means: move forward/backward by a specified number of generations.  For example, if you want to return to the latest generation after --roll-back, use --switch-generation=+1.

     The difference between --roll-back and --switch-generation=-1 is that --switch-generation will not make a zeroth generation, so if a specified generation does not exist, the current generation will not be changed.

--search-paths[=KIND]
     Report environment variable definitions, in Bash syntax, that may be needed in order to use the set of installed packages.  These environment variables are used to specify search paths for files used by some of the installed packages.

     For example, GCC needs the CPATH and LIBRARY_PATH environment variables to be defined so it can look for headers and libraries in the user's profile (see Environment Variables (Using the GNU Compiler Collection (GCC))).  If GCC and, say, the C library are installed in the profile, then --search-paths will suggest setting these variables to PROFILE/include and PROFILE/lib, respectively (see Search Paths, for info on search path specifications associated with packages.)

     The typical use case is to define these environment variables in the shell:

          $ eval $(guix package --search-paths)

     KIND may be one of exact, prefix, or suffix, meaning that the returned environment variable definitions will either be exact settings, or prefixes or suffixes of the current value of these variables.  When omitted, KIND defaults to exact.

     This option can also be used to compute the combined search paths of several profiles.  Consider this example:

          $ guix package -p foo -i guile
          $ guix package -p bar -i guile-json
          $ guix package -p foo -p bar --search-paths

     The last command above reports about the GUILE_LOAD_PATH variable, even though, taken individually, neither foo nor bar would lead to that recommendation.

--profile=PROFILE
-p PROFILE
     Use PROFILE instead of the user's default profile.

     PROFILE must be the name of a file that will be created upon completion.  Concretely, PROFILE will be a mere symbolic link (``symlink'') pointing to the actual profile where packages are installed:

          $ guix install hello -p ~/code/my-profile
          ...
          $ ~/code/my-profile/bin/hello
          Hello, world!

     All it takes to get rid of the profile is to remove this symlink and its siblings that point to specific generations:

          $ rm ~/code/my-profile ~/code/my-profile-*-link

--list-profiles
     List all the user's profiles:

          $ guix package --list-profiles
          /home/charlie/.guix-profile
          /home/charlie/code/my-profile
          /home/charlie/code/devel-profile
          /home/charlie/tmp/test

     When running as root, list all the profiles of all the users.

--allow-collisions
     Allow colliding packages in the new profile.  Use at your own risk!

     By default, guix package reports as an error collisions in the profile.  Collisions happen when two or more different versions or variants of a given package end up in the profile.

--bootstrap
     Use the bootstrap Guile to build the profile.  This option is only useful to distribution developers.

In addition to these actions, guix package supports the following options to query the current state of a profile, or the availability of packages:

--search=REGEXP
-s REGEXP
     List the available packages whose name, synopsis, or description matches REGEXP (in a case-insensitive fashion), sorted by relevance. Print all the metadata of matching packages in recutils format (see GNU recutils databases (GNU recutils manual)).

     This allows specific fields to be extracted using the recsel command, for instance:

          $ guix package -s malloc | recsel -p name,version,relevance
          name: jemalloc
          version: 4.5.0
          relevance: 6

          name: glibc
          version: 2.25
          relevance: 1

          name: libgc
          version: 7.6.0
          relevance: 1

     Similarly, to show the name of all the packages available under the terms of the GNU LGPL version 3:

          $ guix package -s "" | recsel -p name -e 'license ~ "LGPL 3"'
          name: elfutils

          name: gmp
          ...

     It is also possible to refine search results using several -s flags to guix package, or several arguments to guix search.  For example, the following command returns a list of board games (this time using the guix search alias):

          $ guix search '\<board\>' game | recsel -p name
          name: gnubg
          ...

     If we were to omit -s game, we would also get software packages that deal with printed circuit boards; removing the angle brackets around board would further add packages that have to do with keyboards.

     And now for a more elaborate example.  The following command searches for cryptographic libraries, filters out Haskell, Perl, Python, and Ruby libraries, and prints the name and synopsis of the matching packages:

          $ guix search crypto library | \
              recsel -e '! (name ~ "^(ghc|perl|python|ruby)")' -p name,synopsis

     See Selection Expressions (GNU recutils manual), for more information on selection expressions for recsel -e.

--show=PACKAGE
     Show details about PACKAGE, taken from the list of available packages, in recutils format (see GNU recutils databases (GNU recutils manual)).

          $ guix package --show=guile | recsel -p name,version
          name: guile
          version: 3.0.5

          name: guile
          version: 3.0.2

          name: guile
          version: 2.2.7
          ...

     You may also specify the full name of a package to only get details about a specific version of it (this time using the guix show alias):

          $ guix show guile@3.0.5 | recsel -p name,version
          name: guile
          version: 3.0.5

--list-installed[=REGEXP]
-I [REGEXP]
     List the currently installed packages in the specified profile, with the most recently installed packages shown last.  When REGEXP is specified, list only installed packages whose name matches REGEXP.

     For each installed package, print the following items, separated by tabs: the package name, its version string, the part of the package that is installed (for instance, out for the default output, include for its headers, etc.), and the path of this package in the store.

--list-available[=REGEXP]
-A [REGEXP]
     List packages currently available in the distribution for this system (see GNU Distribution).  When REGEXP is specified, list only available packages whose name matches REGEXP.

     For each package, print the following items separated by tabs: its name, its version string, the parts of the package (see Packages with Multiple Outputs), and the source location of its definition.

--list-generations[=PATTERN]
-l [PATTERN]
     Return a list of generations along with their creation dates; for each generation, show the installed packages, with the most recently installed packages shown last.  Note that the zeroth generation is never shown.

     For each installed package, print the following items, separated by tabs: the name of a package, its version string, the part of the package that is installed (see Packages with Multiple Outputs), and the location of this package in the store.

     When PATTERN is used, the command returns only matching generations.  Valid patterns include:

       * Integers and comma-separated integers.  Both patterns denote generation numbers.  For instance, --list-generations=1 returns the first one.

          And --list-generations=1,8,2 outputs three generations in the specified order.  Neither spaces nor trailing commas are allowed.

       * Ranges.  --list-generations=2..9 prints the specified generations and everything in between.  Note that the start of a range must be smaller than its end.

          It is also possible to omit the endpoint.  For example, --list-generations=2.., returns all generations starting from the second one.

       * Durations.  You can also get the last N days, weeks, or months by passing an integer along with the first letter of the duration.  For example, --list-generations=20d lists generations that are up to 20 days old.

--delete-generations[=PATTERN]
-d [PATTERN]
     When PATTERN is omitted, delete all generations except the current one.

     This command accepts the same patterns as --list-generations. When PATTERN is specified, delete the matching generations.  When PATTERN specifies a duration, generations older than the specified duration match.  For instance, --delete-generations=1m deletes generations that are more than one month old.

     If the current generation matches, it is not deleted.  Also, the zeroth generation is never deleted.

     Note that deleting generations prevents rolling back to them. Consequently, this command must be used with care.

--export-manifest
     Write to standard output a manifest suitable for --manifest corresponding to the chosen profile(s).

     This option is meant to help you migrate from the ``imperative'' operating mode---running guix install, guix upgrade, etc.---to the declarative mode that --manifest offers.

     Be aware that the resulting manifest approximates what your profile actually contains; for instance, depending on how your profile was created, it can refer to packages or package versions that are not exactly what you specified.

     Keep in mind that a manifest is purely symbolic: it only contains package names and possibly versions, and their meaning varies over time. If you wish to ``pin'' channels to the revisions that were used to build the profile(s), see --export-channels below.

--export-channels
     Write to standard output the list of channels used by the chosen profile(s), in a format suitable for guix pull --channels or guix time-machine --channels (see Channels).

     Together with --export-manifest, this option provides information allowing you to replicate the current profile (see Replicating Guix).

     However, note that the output of this command approximates what was actually used to build this profile.  In particular, a single profile might have been built from several different revisions of the same channel.  In that case, --export-manifest chooses the last one and writes the list of other revisions in a comment.  If you really need to pick packages from different channel revisions, you can use inferiors in your manifest to do so (see Inferiors).

     Together with --export-manifest, this is a good starting point if you are willing to migrate from the ``imperative'' model to the fully declarative model consisting of a manifest file along with a channels file pinning the exact channel revision(s) you want.

Finally, since guix package may actually start build processes, it supports all the common build options (see Common Build Options).  It also supports package transformation options, such as --with-source, and preserves them across upgrades (see Package Transformation Options).

Substitutes
===========

Guix supports transparent source/binary deployment, which means that it can either build things locally, or download pre-built items from a server, or both.  We call these pre-built items substitutes---they are substitutes for local build results.  In many cases, downloading a substitute is much faster than building things locally.

Substitutes can be anything resulting from a derivation build (see Derivations).  Of course, in the common case, they are pre-built package binaries, but source tarballs, for instance, which also result from derivation builds, can be available as substitutes.

Official Substitute Servers
---------------------------

ci.guix.gnu.org and bordeaux.guix.gnu.org are both front-ends to official build farms that build packages from Guix continuously for some architectures, and make them available as substitutes.  These are the default source of substitutes; which can be overridden by passing the --substitute-urls option either to guix-daemon (see guix-daemon --substitute-urls) or to client tools such as guix package (see client --substitute-urls option).

Substitute URLs can be either HTTP or HTTPS. HTTPS is recommended because communications are encrypted; conversely, using HTTP makes all communications visible to an eavesdropper, who could use the information gathered to determine, for instance, whether your system has unpatched security vulnerabilities.

Substitutes from the official build farms are enabled by default when using Guix System (see GNU Distribution).  However, they are disabled by default when using Guix on a foreign distribution, unless you have explicitly enabled them via one of the recommended installation steps (see Installation).  The following paragraphs describe how to enable or disable substitutes for the official build farm; the same procedure can also be used to enable substitutes for any other substitute server.

Substitute Server Authorization
-------------------------------

To allow Guix to download substitutes from ci.guix.gnu.org, bordeaux.guix.gnu.org or a mirror, you must add the relevant public key to the access control list (ACL) of archive imports, using the guix archive command (see Invoking guix archive).  Doing so implies that you trust the substitute server to not be compromised and to serve genuine substitutes.

     If you are using Guix System, you can skip this section: Guix System authorizes substitutes from ci.guix.gnu.org and bordeaux.guix.gnu.org by default.

The public keys for each of the project maintained substitute servers are installed along with Guix, in PREFIX/share/guix/, where PREFIX is the installation prefix of Guix.  If you installed Guix from source, make sure you checked the GPG signature of guix-VERSION.tar.gz, which contains this public key file. Then, you can run something like this:

     # guix archive --authorize < PREFIX/share/guix/ci.guix.gnu.org.pub
     # guix archive --authorize < PREFIX/share/guix/bordeaux.guix.gnu.org.pub

Once this is in place, the output of a command like guix build should change from something like:

     $ guix build emacs --dry-run
     The following derivations would be built:
        /gnu/store/yr7bnx8xwcayd6j95r2clmkdl1qh688w-emacs-24.3.drv
        /gnu/store/x8qsh1hlhgjx6cwsjyvybnfv2i37z23w-dbus-1.6.4.tar.gz.drv
        /gnu/store/1ixwp12fl950d15h2cj11c73733jay0z-alsa-lib-1.0.27.1.tar.bz2.drv
        /gnu/store/nlma1pw0p603fpfiqy7kn4zm105r5dmw-util-linux-2.21.drv
     ...

to something like:

     $ guix build emacs --dry-run
     112.3 MB would be downloaded:
        /gnu/store/pk3n22lbq6ydamyymqkkz7i69wiwjiwi-emacs-24.3
        /gnu/store/2ygn4ncnhrpr61rssa6z0d9x22si0va3-libjpeg-8d
        /gnu/store/71yz6lgx4dazma9dwn2mcjxaah9w77jq-cairo-1.12.16
        /gnu/store/7zdhgp0n1518lvfn8mb96sxqfmvqrl7v-libxrender-0.9.7
     ...

The text changed from ``The following derivations would be built'' to ``112.3 MB would be downloaded''.  This indicates that substitutes from the configured substitute servers are usable and will be downloaded, when possible, for future builds.

The substitute mechanism can be disabled globally by running guix-daemon with --no-substitutes (see Invoking guix-daemon).  It can also be disabled temporarily by passing the --no-substitutes option to guix package, guix build, and other command-line tools.

Getting Substitutes from Other Servers
--------------------------------------

Guix can look up and fetch substitutes from several servers.  This is useful when you are using packages from additional channels for which the official server does not have substitutes but another server provides them.  Another situation where this is useful is when you would prefer to download from your organization's substitute server, resorting to the official server only as a fallback or dismissing it altogether.

You can give Guix a list of substitute server URLs and it will check them in the specified order.  You also need to explicitly authorize the public keys of substitute servers to instruct Guix to accept the substitutes they sign.

On Guix System, this is achieved by modifying the configuration of the guix service.  Since the guix service is part of the default lists of services, %base-services and %desktop-services, you can use modify-services to change its configuration and add the URLs and substitute keys that you want (see modify-services).

As an example, suppose you want to fetch substitutes from guix.example.org and to authorize the signing key of that server, in addition to the default ci.guix.gnu.org and bordeaux.guix.gnu.org.  The resulting operating system configuration will look something like:

     (operating-system
       ;; ...
       (services
         ;; Assume we're starting from '%desktop-services'.  Replace it
         ;; with the list of services you're actually using.
         (modify-services %desktop-services
           (guix-service-type config =>
                             (guix-configuration
                               (inherit config)
                               (substitute-urls
                                 (append (list "https://guix.example.org")
                                         %default-substitute-urls))
                               (authorized-keys
                                 (append (list (local-file "./key.pub"))
                                         %default-authorized-guix-keys)))))))

This assumes that the file key.pub contains the signing key of guix.example.org.  With this change in place in your operating system configuration file (say /etc/config.scm), you can reconfigure and restart the guix-daemon service or reboot so the changes take effect:

     $ sudo guix system reconfigure /etc/config.scm
     $ sudo herd restart guix-daemon

If you're running Guix on a ``foreign distro'', you would instead take the following steps to get substitutes from additional servers:

 1. Edit the service configuration file for guix-daemon; when using systemd, this is normally /etc/systemd/system/guix-daemon.service.  Add the --substitute-urls option on the guix-daemon command line and list the URLs of interest (see guix-daemon --substitute-urls):

          ... --substitute-urls='https://guix.example.org https://ci.guix.gnu.org https://bordeaux.guix.gnu.org'

 2. Restart the daemon.  For systemd, it goes like this:

          systemctl daemon-reload
          systemctl restart guix-daemon.service

 3. Authorize the key of the new server (see Invoking guix archive):

          guix archive --authorize < key.pub

     Again this assumes key.pub contains the public key that guix.example.org uses to sign substitutes.

Now you're all set!  Substitutes will be preferably taken from https://guix.example.org, using ci.guix.gnu.org then bordeaux.guix.gnu.org as fallback options.  Of course you can list as many substitute servers as you like, with the caveat that substitute lookup can be slowed down if too many servers need to be contacted.

     To diagnose problems, you can run guix weather.  For example, running:

          guix weather coreutils

     not only tells you which of the currently-configured servers has substitutes for the coreutils package, it also reports whether one of these servers is unauthorized.  See Invoking guix weather, for more information.

Note that there are also situations where one may want to add the URL of a substitute server without authorizing its key. See Substitute Authentication, to understand this fine point.

Substitute Authentication
-------------------------

Guix detects and raises an error when attempting to use a substitute that has been tampered with.  Likewise, it ignores substitutes that are not signed, or that are not signed by one of the keys listed in the ACL.

There is one exception though: if an unauthorized server provides substitutes that are bit-for-bit identical to those provided by an authorized server, then the unauthorized server becomes eligible for downloads.  For example, assume we have chosen two substitute servers with this option:

     --substitute-urls="https://a.example.org https://b.example.org"

If the ACL contains only the key for b.example.org, and if a.example.org happens to serve the exact same substitutes, then Guix will download substitutes from a.example.org because it comes first in the list and can be considered a mirror of b.example.org.  In practice, independent build machines usually produce the same binaries, thanks to bit-reproducible builds (see below).

When using HTTPS, the server's X.509 certificate is not validated (in other words, the server is not authenticated), contrary to what HTTPS clients such as Web browsers usually do.  This is because Guix authenticates substitute information itself, as explained above, which is what we care about (whereas X.509 certificates are about authenticating bindings between domain names and public keys).

Proxy Settings
--------------

Substitutes are downloaded over HTTP or HTTPS.  The http_proxy and https_proxy environment variables can be set in the environment of guix-daemon and are honored for downloads of substitutes. Note that the value of those environment variables in the environment where guix build, guix package, and other client commands are run has absolutely no effect.

Substitution Failure
--------------------

Even when a substitute for a derivation is available, sometimes the substitution attempt will fail.  This can happen for a variety of reasons: the substitute server might be offline, the substitute may recently have been deleted, the connection might have been interrupted, etc.

When substitutes are enabled and a substitute for a derivation is available, but the substitution attempt fails, Guix will attempt to build the derivation locally depending on whether or not --fallback was given (see common build option --fallback).  Specifically, if --fallback was omitted, then no local build will be performed, and the derivation is considered to have failed.  However, if --fallback was given, then Guix will attempt to build the derivation locally, and the success or failure of the derivation depends on the success or failure of the local build.  Note that when substitutes are disabled or no substitute is available for the derivation in question, a local build will always be performed, regardless of whether or not --fallback was given.

To get an idea of how many substitutes are available right now, you can try running the guix weather command (see Invoking guix weather).  This command provides statistics on the substitutes provided by a server.

On Trusting Binaries
--------------------

Today, each individual's control over their own computing is at the mercy of institutions, corporations, and groups with enough power and determination to subvert the computing infrastructure and exploit its weaknesses.  While using substitutes can be convenient, we encourage users to also build on their own, or even run their own build farm, such that the project run substitute servers are less of an interesting target.  One way to help is by publishing the software you build using guix publish so that others have one more choice of server to download substitutes from (see Invoking guix publish).

Guix has the foundations to maximize build reproducibility (see Features).  In most cases, independent builds of a given package or derivation should yield bit-identical results.  Thus, through a diverse set of independent package builds, we can strengthen the integrity of our systems.  The guix challenge command aims to help users assess substitute servers, and to assist developers in finding out about non-deterministic package builds (see Invoking guix challenge).  Similarly, the --check option of guix build allows users to check whether previously-installed substitutes are genuine by rebuilding them locally (see guix build --check).

In the future, we want Guix to have support to publish and retrieve binaries to/from other users, in a peer-to-peer fashion.  If you would like to discuss this project, join us on guix-devel@gnu.org.

Packages with Multiple Outputs
==============================

Often, packages defined in Guix have a single output---i.e., the source package leads to exactly one directory in the store.  When running guix install glibc, one installs the default output of the GNU libc package; the default output is called out, but its name can be omitted as shown in this command.  In this particular case, the default output of glibc contains all the C header files, shared libraries, static libraries, Info documentation, and other supporting files.

Sometimes it is more appropriate to separate the various types of files produced from a single source package into separate outputs.  For instance, the GLib C library (used by GTK+ and related packages) installs more than 20 MiB of reference documentation as HTML pages. To save space for users who do not need it, the documentation goes to a separate output, called doc.  To install the main GLib output, which contains everything but the documentation, one would run:

     guix install glib

The command to install its documentation is:

     guix install glib:doc

While the colon syntax works for command-line specification of package outputs, it will not work when using a package variable in Scheme code.  For example, to add the documentation of glib to the globally installed packages of an operating-system (see operating-system Reference), a list of two items, the first one being the package variable and the second one the name of the output to select (a string), must be used instead:

     (use-modules (gnu packages glib))
     ;; glib-with-documentation is the Guile symbol for the glib package
     (operating-system
      ...
      (packages
       (append
        (list (list glib-with-documentation "doc"))
              %base-packages)))

Some packages install programs with different ``dependency footprints''. For instance, the WordNet package installs both command-line tools and graphical user interfaces (GUIs).  The former depend solely on the C library, whereas the latter depend on Tcl/Tk and the underlying X libraries.  In this case, we leave the command-line tools in the default output, whereas the GUIs are in a separate output.  This allows users who do not need the GUIs to save space.  The guix size command can help find out about such situations (see Invoking guix size). guix graph can also be helpful (see Invoking guix graph).

There are several such multiple-output packages in the GNU distribution. Other conventional output names include lib for libraries and possibly header files, bin for stand-alone programs, and debug for debugging information (see Installing Debugging Files).  The outputs of a package are listed in the third column of the output of guix package --list-available (see Invoking guix package).

Invoking guix locate
====================

There's so much free software out there that sooner or later, you will need to search for packages.  The guix search command that we've seen before (see Invoking guix package) lets you search by keywords:

     guix search video editor

Sometimes, you instead want to find which package provides a given file, and this is where guix locate comes in.  Here is how you can find which package provides the ls command:

     $ guix locate ls
     coreutils@9.1       /gnu/store/...-coreutils-9.1/bin/ls

Of course the command works for any file, not just commands:

     $ guix locate unistr.h
     icu4c@71.1          /gnu/store/.../include/unicode/unistr.h
     libunistring@1.0    /gnu/store/.../include/unistr.h

You may also specify glob patterns with wildcards.  For example, here is how you would search for packages providing .service files:

     $ guix locate -g '*.service'
     man-db@2.11.1        .../lib/systemd/system/man-db.service
     wpa-supplicant@2.10  .../system-services/fi.w1.wpa_supplicant1.service

The guix locate command relies on a database that maps file names to package names.  By default, it automatically creates that database if it does not exist yet by traversing packages available locally, which can take a few minutes (depending on the size of your store and the speed of your storage device).

     For now, guix locate builds its database based on purely local knowledge---meaning that you will not find packages that never reached your store.  Eventually it will support downloading a pre-built database so you can potentially find more packages.

By default, guix locate first tries to look for a system-wide database, usually under /var/cache/guix/locate; if it does not exist or is too old, it falls back to the per-user database, by default under ~/.cache/guix/locate.  On a multi-user system, administrators may want to periodically update the system-wide database so that all users can benefit from it, for instance by setting up package-database-service-type (see package-database-service-type).

The general syntax is:

     guix locate [OPTIONS...] FILE...

... where FILE is the name of a file to search for (specifically, the ``base name'' of the file: files whose parent directories are called FILE are not matched).

The available options are as follows:

--glob

-g
     Interpret FILE... as glob patterns---patterns that may include wildcards, such as *.scm to denote all files ending in .scm.

--stats
     Display database statistics.

--update
-u
     Update the file database.

     By default, the database is automatically updated when it is too old.

--clear
     Clear the database and re-populate it.

     This option lets you start anew, ensuring old data is removed from the database, which also avoids having an endlessly growing database.  By default guix locate automatically does that periodically, though infrequently.

--database=FILE
     Use FILE as the database, creating it if necessary.

     By default, guix locate picks the database under ~/.cache/guix or /var/cache/guix, whichever is the most recent one.

--method=METHOD
-m METHOD
     Use METHOD to select the set of packages to index.  Possible values are:

     manifests
          This is the default method: it works by traversing profiles on the machine and recording packages it encounters---packages you or other users of the machine installed, directly or indirectly.  It is fast but it can miss other packages available in the store but not referred to by any profile.

     store
          This is a slower but more exhaustive method: it checks among all the existing packages those that are available in the store and records them.

Invoking guix gc
================

Packages that are installed, but not used, may be garbage-collected. The guix gc command allows users to explicitly run the garbage collector to reclaim space from the /gnu/store directory.  It is the only way to remove files from /gnu/store---removing files or directories manually may break it beyond repair!

The garbage collector has a set of known roots: any file under /gnu/store reachable from a root is considered live and cannot be deleted; any other file is considered dead and may be deleted.  The set of garbage collector roots (``GC roots'' for short) includes default user profiles; by default, the symlinks under /var/guix/gcroots represent these GC roots.  New GC roots can be added with guix build --root, for example (see Invoking guix build).  The guix gc --list-roots command lists them.

Prior to running guix gc --collect-garbage to make space, it is often useful to remove old generations from user profiles; that way, old package builds referenced by those generations can be reclaimed.  This is achieved by running guix package --delete-generations (see Invoking guix package).

Our recommendation is to run a garbage collection periodically, or when you are short on disk space.  For instance, to guarantee that at least 5 GB are available on your disk, simply run:

     guix gc -F 5G

It is perfectly safe to run as a non-interactive periodic job (see Scheduled Job Execution, for how to set up such a job). Running guix gc with no arguments will collect as much garbage as it can, but that is often inconvenient: you may find yourself having to rebuild or re-download software that is ``dead'' from the GC viewpoint but that is necessary to build other pieces of software---e.g., the compiler tool chain.

The guix gc command has three modes of operation: it can be used to garbage-collect any dead files (the default), to delete specific files (the --delete option), to print garbage-collector information, or for more advanced queries.  The garbage collection options are as follows:

--collect-garbage[=MIN]
-C [MIN]
     Collect garbage---i.e., unreachable /gnu/store files and sub-directories.  This is the default operation when no option is specified.

     When MIN is given, stop once MIN bytes have been collected. MIN may be a number of bytes, or it may include a unit as a suffix, such as MiB for mebibytes and GB for gigabytes (see size specifications (GNU Coreutils)).

     When MIN is omitted, collect all the garbage.

--free-space=FREE
-F FREE
     Collect garbage until FREE space is available under /gnu/store, if possible; FREE denotes storage space, such as 500MiB, as described above.

     When FREE or more is already available in /gnu/store, do nothing and exit immediately.

--delete-generations[=DURATION]
-d [DURATION]
     Before starting the garbage collection process, delete all the generations older than DURATION, for all the user profiles and home environment generations; when run as root, this applies to all the profiles of all the users.

     For example, this command deletes all the generations of all your profiles that are older than 2 months (except generations that are current), and then proceeds to free space until at least 10 GiB are available:

          guix gc -d 2m -F 10G

--delete
-D
     Attempt to delete all the store files and directories specified as arguments.  This fails if some of the files are not in the store, or if they are still live.

--list-failures
     List store items corresponding to cached build failures.

     This prints nothing unless the daemon was started with --cache-failures (see --cache-failures).

--list-roots
     List the GC roots owned by the user; when run as root, list all the GC roots.

--list-busy
     List store items in use by currently running processes.  These store items are effectively considered GC roots: they cannot be deleted.

--clear-failures
     Remove the specified store items from the failed-build cache.

     Again, this option only makes sense when the daemon is started with --cache-failures.  Otherwise, it does nothing.

--list-dead
     Show the list of dead files and directories still present in the store---i.e., files and directories no longer reachable from any root.

--list-live
     Show the list of live store files and directories.

In addition, the references among existing store files can be queried:

--references
--referrers
     List the references (respectively, the referrers) of store files given as arguments.

--requisites
-R
     List the requisites of the store files passed as arguments.  Requisites include the store files themselves, their references, and the references of these, recursively.  In other words, the returned list is the transitive closure of the store files.

     See Invoking guix size, for a tool to profile the size of the closure of an element.  See Invoking guix graph, for a tool to visualize the graph of references.

--derivers
     Return the derivation(s) leading to the given store items (see Derivations).

     For example, this command:

          guix gc --derivers $(guix package -I ^emacs$ | cut -f4)

     returns the .drv file(s) leading to the emacs package installed in your profile.

     Note that there may be zero matching .drv files, for instance because these files have been garbage-collected.  There can also be more than one matching .drv due to fixed-output derivations.

Lastly, the following options allow you to check the integrity of the store and to control disk usage.

--verify[=OPTIONS]
     Verify the integrity of the store.

     By default, make sure that all the store items marked as valid in the database of the daemon actually exist in /gnu/store.

     When provided, OPTIONS must be a comma-separated list containing one or more of contents and repair.

     When passing --verify=contents, the daemon computes the content hash of each store item and compares it against its hash in the database.  Hash mismatches are reported as data corruptions.  Because it traverses all the files in the store, this command can take a long time, especially on systems with a slow disk drive.

     Using --verify=repair or --verify=contents,repair causes the daemon to try to repair corrupt store items by fetching substitutes for them (see Substitutes).  Because repairing is not atomic, and thus potentially dangerous, it is available only to the system administrator.  A lightweight alternative, when you know exactly which items in the store are corrupt, is guix build --repair (see Invoking guix build).

--optimize
     Optimize the store by hard-linking identical files---this is deduplication.

     The daemon performs deduplication after each successful build or archive import, unless it was started with --disable-deduplication (see --disable-deduplication).  Thus, this option is primarily useful when the daemon was running with --disable-deduplication.

--vacuum-database
     Guix uses an sqlite database to keep track of the items in (see The Store). Over time it is possible that the database may grow to a large size and become fragmented.  As a result, one may wish to clear the freed space and join the partially used pages in the database left behind from removed packages or after running the garbage collector.  Running sudo guix gc --vacuum-database will lock the database and VACUUM the store, defragmenting the database and purging freed pages, unlocking the database when it finishes.

Invoking guix pull
==================

Packages are installed or upgraded to the latest version available in the distribution currently available on your local machine.  To update that distribution, along with the Guix tools, you must run guix pull: the command downloads the latest Guix source code and package descriptions, and deploys it.  Source code is downloaded from a Git (https://git-scm.com/book/en/) repository, by default the official GNU Guix repository, though this can be customized.  guix pull ensures that the code it downloads is authentic by verifying that commits are signed by Guix developers.

Specifically, guix pull downloads code from the channels (see Channels) specified by one of the following, in this order:

 1. the --channels option;

 2. the user's ~/.config/guix/channels.scm file, unless -q is passed;

 3. the system-wide /etc/guix/channels.scm file, unless -q is passed;

 4. the built-in default channels specified in the %default-channels variable.

On completion, guix package will use packages and package versions from this just-retrieved copy of Guix.  Not only that, but all the Guix commands and Scheme modules will also be taken from that latest version.  New guix sub-commands added by the update also become available.

Any user can update their Guix copy using guix pull, and the effect is limited to the user who ran guix pull.  For instance, when user root runs guix pull, this has no effect on the version of Guix that user alice sees, and vice versa.

The result of running guix pull is a profile available under ~/.config/guix/current containing the latest Guix.  Thus, make sure to add it to the beginning of your search path so that you use the latest version, and similarly for the Info manual (see Documentation):

     export PATH="$HOME/.config/guix/current/bin:$PATH"
     export INFOPATH="$HOME/.config/guix/current/share/info:$INFOPATH"

The --list-generations or -l option lists past generations produced by guix pull, along with details about their provenance:

     $ guix pull -l
     Generation 1	Jun 10 2018 00:18:18
       guix 65956ad
         repository URL: https://git.savannah.gnu.org/git/guix.git
         branch: origin/master
         commit: 65956ad3526ba09e1f7a40722c96c6ef7c0936fe

     Generation 2	Jun 11 2018 11:02:49
       guix e0cc7f6
         repository URL: https://git.savannah.gnu.org/git/guix.git
         branch: origin/master
         commit: e0cc7f669bec22c37481dd03a7941c7d11a64f1d

     Generation 3	Jun 13 2018 23:31:07	(current)
       guix 844cc1c
         repository URL: https://git.savannah.gnu.org/git/guix.git
         branch: origin/master
         commit: 844cc1c8f394f03b404c5bb3aee086922373490c

See guix describe, for other ways to describe the current status of Guix.

This ~/.config/guix/current profile works exactly like the profiles created by guix package (see Invoking guix package).  That is, you can list generations, roll back to the previous generation---i.e., the previous Guix---and so on:

     $ guix pull --roll-back
     switched from generation 3 to 2
     $ guix pull --delete-generations=1
     deleting /var/guix/profiles/per-user/charlie/current-guix-1-link

You can also use guix package (see Invoking guix package) to manage the profile by naming it explicitly:

     $ guix package -p ~/.config/guix/current --roll-back
     switched from generation 3 to 2
     $ guix package -p ~/.config/guix/current --delete-generations=1
     deleting /var/guix/profiles/per-user/charlie/current-guix-1-link

The guix pull command is usually invoked with no arguments, but it supports the following options:

--url=URL
--commit=COMMIT
--branch=BRANCH
     Download code for the guix channel from the specified URL, at the given COMMIT (a valid Git commit ID represented as a hexadecimal string or the name of a tag), or BRANCH.

     These options are provided for convenience, but you can also specify your configuration in the ~/.config/guix/channels.scm file or using the --channels option (see below).

--channels=FILE
-C FILE
     Read the list of channels from FILE instead of ~/.config/guix/channels.scm or /etc/guix/channels.scm. FILE must contain Scheme code that evaluates to a list of channel objects.  See Channels, for more information.

--no-channel-files
-q
     Inhibit loading of the user and system channel files, ~/.config/guix/channels.scm and /etc/guix/channels.scm.

--news
-N
     Display news written by channel authors for their users for changes made since the previous generation (see Writing Channel News). When --details is passed, additionally display new and upgraded packages.

     You can view that information for previous generations with guix pull -l.

--list-generations[=PATTERN]
-l [PATTERN]
     List all the generations of ~/.config/guix/current or, if PATTERN is provided, the subset of generations that match PATTERN. The syntax of PATTERN is the same as with guix package --list-generations (see Invoking guix package).

     By default, this prints information about the channels used in each revision as well as the corresponding news entries.  If you pass --details, it will also print the list of packages added and upgraded in each generation compared to the previous one.

--details
     Instruct --list-generations or --news to display more information about the differences between subsequent generations---see above.

--roll-back
     Roll back to the previous generation of ~/.config/guix/current---i.e., undo the last transaction.

--switch-generation=PATTERN
-S PATTERN
     Switch to a particular generation defined by PATTERN.

     PATTERN may be either a generation number or a number prefixed with ``+'' or ``-''.  The latter means: move forward/backward by a specified number of generations.  For example, if you want to return to the latest generation after --roll-back, use --switch-generation=+1.

--delete-generations[=PATTERN]
-d [PATTERN]
     When PATTERN is omitted, delete all generations except the current one.

     This command accepts the same patterns as --list-generations. When PATTERN is specified, delete the matching generations.  When PATTERN specifies a duration, generations older than the specified duration match.  For instance, --delete-generations=1m deletes generations that are more than one month old.

     If the current generation matches, it is not deleted.

     Note that deleting generations prevents rolling back to them. Consequently, this command must be used with care.

     See Invoking guix describe, for a way to display information about the current generation only.

--profile=PROFILE
-p PROFILE
     Use PROFILE instead of ~/.config/guix/current.

--dry-run
-n
     Show which channel commit(s) would be used and what would be built or substituted but do not actually do it.

--allow-downgrades
     Allow pulling older or unrelated revisions of channels than those currently in use.

     By default, guix pull protects against so-called ``downgrade attacks'' whereby the Git repository of a channel would be reset to an earlier or unrelated revision of itself, potentially leading you to install older, known-vulnerable versions of software packages.

          Make sure you understand its security implications before using --allow-downgrades.

--disable-authentication
     Allow pulling channel code without authenticating it.

     By default, guix pull authenticates code downloaded from channels by verifying that its commits are signed by authorized developers, and raises an error if this is not the case.  This option instructs it to not perform any such verification.

          Make sure you understand its security implications before using --disable-authentication.

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., i686-linux---instead of the system type of the build host.

--bootstrap
     Use the bootstrap Guile to build the latest Guix.  This option is only useful to Guix developers.

The channel mechanism allows you to instruct guix pull which repository and branch to pull from, as well as additional repositories containing package modules that should be deployed.  See Channels, for more information.

In addition, guix pull supports all the common build options (see Common Build Options).

Invoking guix time-machine
==========================

The guix time-machine command provides access to other revisions of Guix, for example to install older versions of packages, or to reproduce a computation in an identical environment.  The revision of Guix to be used is defined by a commit or by a channel description file created by guix describe (see Invoking guix describe).

Let's assume that you want to travel to those days of November 2020 when version 1.2.0 of Guix was released and, once you're there, run the guile of that time:

     guix time-machine --commit=v1.2.0 -- \
       environment -C --ad-hoc guile -- guile

The command above fetches Guix 1.2.0 (and possibly other channels specified by your channels.scm configuration files---see below) and runs its guix environment command to spawn an environment in a container running guile (guix environment has since been subsumed by guix shell; see Invoking guix shell).  It's like driving a DeLorean (If you don't know what a DeLorean is, consider traveling back to the 1980's. (Back to the Future (1985) (https://www.imdb.com/title/tt0088763/)))!  The first guix time-machine invocation can be expensive: it may have to download or even build a large number of packages; the result is cached though and subsequent commands targeting the same commit are almost instantaneous.

As for guix pull, in the absence of any options, time-machine fetches the latest commits of the channels specified in ~/.config/guix/channels.scm, /etc/guix/channels.scm, or the default channels; the -q option lets you ignore these configuration files.  The command:

     guix time-machine -q -- build hello

will thus build the package hello as defined in the main branch of Guix, without any additional channel, which is in general a newer revision of Guix than you have installed.  Time travel works in both directions!

     The history of Guix is immutable and guix time-machine provides the exact same software as they are in a specific Guix revision.  Naturally, no security fixes are provided for old versions of Guix or its channels.  A careless use of guix time-machine opens the door to security vulnerabilities.  See --allow-downgrades.

Due to guix time-machine relying on the ``inferiors'' mechanism (see Inferiors), the oldest commit it can travel to is commit 6298c3ff (``v1.0.0''), dated May 1st, 2019, which is the first release that included the inferiors mechanism.  An error is returned when attempting to navigate to older commits.

     Although it should technically be possible to travel to such an old commit, the ease to do so will largely depend on the availability of binary substitutes.  When traveling to a distant past, some packages may not easily build from source anymore.  One such example are old versions of Python 2 which had time bombs in its test suite, in the form of expiring SSL certificates.  This particular problem can be worked around by setting the hardware clock to a value in the past before attempting the build.

The general syntax is:

     guix time-machine OPTIONS... -- COMMAND {arg}...

where COMMAND and ARG... are passed unmodified to the guix command of the specified revision.  The OPTIONS that define this revision are the same as for guix pull (see Invoking guix pull):

--url=URL
--commit=COMMIT
--branch=BRANCH
     Use the guix channel from the specified URL, at the given COMMIT (a valid Git commit ID represented as a hexadecimal string or the name of a tag), or BRANCH.

--channels=FILE
-C FILE
     Read the list of channels from FILE.  FILE must contain Scheme code that evaluates to a list of channel objects. See Channels for more information.

--no-channel-files
-q
     Inhibit loading of the user and system channel files, ~/.config/guix/channels.scm and /etc/guix/channels.scm.

     Thus, guix time-machine -q is equivalent to the following Bash command, using the ``process substitution'' syntax (see Process Substitution (The GNU Bash Reference Manual)):

          guix time-machine -C <(echo %default-channels) ...

Note that guix time-machine can trigger builds of channels and their dependencies, and these are controlled by the standard build options (see Common Build Options).

Inferiors
=========

     The functionality described here is a ``technology preview'' as of version VERSION.  As such, the interface is subject to change.

Sometimes you might need to mix packages from the revision of Guix you're currently running with packages available in a different revision of Guix. Guix inferiors allow you to achieve that by composing different Guix revisions in arbitrary ways.

Technically, an ``inferior'' is essentially a separate Guix process connected to your main Guix process through a REPL (see Invoking guix repl).  The (guix inferior) module allows you to create inferiors and to communicate with them.  It also provides a high-level interface to browse and manipulate the packages that an inferior provides---inferior packages.

When combined with channels (see Channels), inferiors provide a simple way to interact with a separate revision of Guix.  For example, let's assume you want to install in your profile the current guile package, along with the guile-json as it existed in an older revision of Guix---perhaps because the newer guile-json has an incompatible API and you want to run your code against the old API.  To do that, you could write a manifest for use by guix package --manifest (see Writing Manifests); in that manifest, you would create an inferior for that old Guix revision you care about, and you would look up the guile-json package in the inferior:

     (use-modules (guix inferior) (guix channels)
                  (srfi srfi-1))   ;for 'first'

     (define channels
       ;; This is the old revision from which we want to
       ;; extract guile-json.
       (list (channel
              (name 'guix)
              (url "https://git.savannah.gnu.org/git/guix.git")
              (commit
               "65956ad3526ba09e1f7a40722c96c6ef7c0936fe"))))

     (define inferior
       ;; An inferior representing the above revision.
       (inferior-for-channels channels))

     ;; Now create a manifest with the current "guile" package
     ;; and the old "guile-json" package.
     (packages->manifest
      (list (first (lookup-inferior-packages inferior "guile-json"))
            (specification->package "guile")))

On its first run, guix package --manifest might have to build the channel you specified before it can create the inferior; subsequent runs will be much faster because the Guix revision will be cached.

The (guix inferior) module provides the following procedures to open an inferior:

 -- Procedure: inferior-for-channels channels [#:cache-directory] [#:ttl]
     Return an inferior for CHANNELS, a list of channels.  Use the cache at CACHE-DIRECTORY, where entries can be reclaimed after TTL seconds. This procedure opens a new connection to the build daemon.

     As a side effect, this procedure may build or substitute binaries for CHANNELS, which can take time.

 -- Procedure: open-inferior directory [#:command "bin/guix"]
     Open the inferior Guix in DIRECTORY, running DIRECTORY/COMMAND repl or equivalent.  Return #f if the inferior could not be launched.

The procedures listed below allow you to obtain and manipulate inferior packages.

 -- Procedure: inferior-packages inferior
     Return the list of packages known to INFERIOR.

 -- Procedure: lookup-inferior-packages inferior name [version]
     Return the sorted list of inferior packages matching NAME in INFERIOR, with highest version numbers first.  If VERSION is true, return only packages with a version number prefixed by VERSION.

 -- Procedure: inferior-package? obj
     Return true if OBJ is an inferior package.

 -- Procedure: inferior-package-name package
 -- Procedure: inferior-package-version package
 -- Procedure: inferior-package-synopsis package
 -- Procedure: inferior-package-description package
 -- Procedure: inferior-package-home-page package
 -- Procedure: inferior-package-location package
 -- Procedure: inferior-package-inputs package
 -- Procedure: inferior-package-native-inputs package
 -- Procedure: inferior-package-propagated-inputs package
 -- Procedure: inferior-package-transitive-propagated-inputs package
 -- Procedure: inferior-package-native-search-paths package
 -- Procedure: inferior-package-transitive-native-search-paths package
 -- Procedure: inferior-package-search-paths package
     These procedures are the counterpart of package record accessors (see package Reference).  Most of them work by querying the inferior PACKAGE comes from, so the inferior must still be live when you call these procedures.

Inferior packages can be used transparently like any other package or file-like object in G-expressions (see G-Expressions).  They are also transparently handled by the packages->manifest procedure, which is commonly used in manifests (see the --manifest option of guix package).  Thus you can insert an inferior package pretty much anywhere you would insert a regular package: in manifests, in the packages field of your operating-system declaration, and so on.

Invoking guix describe
======================

Often you may want to answer questions like: ``Which revision of Guix am I using?'' or ``Which channels am I using?''  This is useful information in many situations: if you want to replicate an environment on a different machine or user account, if you want to report a bug or to determine what change in the channels you are using caused it, or if you want to record your system state for reproducibility purposes.  The guix describe command answers these questions.

When run from a guix pulled guix, guix describe displays the channel(s) that it was built from, including their repository URL and commit IDs (see Channels):

     $ guix describe
     Generation 10	Sep 03 2018 17:32:44	(current)
       guix e0fa68c
         repository URL: https://git.savannah.gnu.org/git/guix.git
         branch: master
         commit: e0fa68c7718fffd33d81af415279d6ddb518f727

If you're familiar with the Git version control system, this is similar in spirit to git describe; the output is also similar to that of guix pull --list-generations, but limited to the current generation (see the --list-generations option).  Because the Git commit ID shown above unambiguously refers to a snapshot of Guix, this information is all it takes to describe the revision of Guix you're using, and also to replicate it.

To make it easier to replicate Guix, guix describe can also be asked to return a list of channels instead of the human-readable description above:

     $ guix describe -f channels
     (list (channel
             (name 'guix)
             (url "https://git.savannah.gnu.org/git/guix.git")
             (commit
               "e0fa68c7718fffd33d81af415279d6ddb518f727")
             (introduction
               (make-channel-introduction
                 "9edb3f66fd807b096b48283debdcddccfea34bad"
                 (openpgp-fingerprint
                   "BBB0 2DDF 2CEA F6A8 0D1D  E643 A2A0 6DF2 A33A 54FA")))))

You can save this to a file and feed it to guix pull -C on some other machine or at a later point in time, which will instantiate this exact Guix revision (see the -C option). From there on, since you're able to deploy the same revision of Guix, you can just as well replicate a complete software environment.  We humbly think that this is awesome, and we hope you'll like it too!

The details of the options supported by guix describe are as follows:

--format=FORMAT
-f FORMAT
     Produce output in the specified FORMAT, one of:

     human
          produce human-readable output;

     channels
          produce a list of channel specifications that can be passed to guix pull -C or installed as ~/.config/guix/channels.scm (see Invoking guix pull);

     channels-sans-intro
          like channels, but omit the introduction field; use it to produce a channel specification suitable for Guix version 1.1.0 or earlier---the introduction field has to do with channel authentication (see Channel Authentication) and is not supported by these older versions;

     json
          produce a list of channel specifications in JSON format;

     recutils
          produce a list of channel specifications in Recutils format.

--list-formats
     Display available formats for --format option.

--profile=PROFILE
-p PROFILE
     Display information about PROFILE.

Invoking guix archive
=====================

The guix archive command allows users to export files from the store into a single archive, and to later import them on a machine that runs Guix. In particular, it allows store files to be transferred from one machine to the store on another machine.

     If you're looking for a way to produce archives in a format suitable for tools other than Guix, see Invoking guix pack.

To export store files as an archive to standard output, run:

     guix archive --export OPTIONS SPECIFICATIONS...

SPECIFICATIONS may be either store file names or package specifications, as for guix package (see Invoking guix package).  For instance, the following command creates an archive containing the gui output of the git package and the main output of emacs:

     guix archive --export git:gui /gnu/store/...-emacs-24.3 > great.nar

If the specified packages are not built yet, guix archive automatically builds them.  The build process may be controlled with the common build options (see Common Build Options).

To transfer the emacs package to a machine connected over SSH, one would run:

     guix archive --export -r emacs | ssh the-machine guix archive --import

Similarly, a complete user profile may be transferred from one machine to another like this:

     guix archive --export -r $(readlink -f ~/.guix-profile) | \
       ssh the-machine guix archive --import

However, note that, in both examples, all of emacs and the profile as well as all of their dependencies are transferred (due to -r), regardless of what is already available in the store on the target machine.  The --missing option can help figure out which items are missing from the target store.  The guix copy command simplifies and optimizes this whole process, so this is probably what you should use in this case (see Invoking guix copy).

Each store item is written in the normalized archive or nar format (described below), and the output of guix archive --export (and input of guix archive --import) is a nar bundle.

The nar format is comparable in spirit to `tar', but with differences that make it more appropriate for our purposes.  First, rather than recording all Unix metadata for each file, the nar format only mentions the file type (regular, directory, or symbolic link); Unix permissions and owner/group are dismissed.  Second, the order in which directory entries are stored always follows the order of file names according to the C locale collation order.  This makes archive production fully deterministic.

That nar bundle format is essentially the concatenation of zero or more nars along with metadata for each store item it contains: its file name, references, corresponding derivation, and a digital signature.

When exporting, the daemon digitally signs the contents of the archive, and that digital signature is appended.  When importing, the daemon verifies the signature and rejects the import in case of an invalid signature or if the signing key is not authorized.

The main options are:

--export
     Export the specified store files or packages (see below).  Write the resulting archive to the standard output.

     Dependencies are not included in the output, unless --recursive is passed.

-r
--recursive
     When combined with --export, this instructs guix archive to include dependencies of the given items in the archive.  Thus, the resulting archive is self-contained: it contains the closure of the exported store items.

--import
     Read an archive from the standard input, and import the files listed therein into the store.  Abort if the archive has an invalid digital signature, or if it is signed by a public key not among the authorized keys (see --authorize below).

--missing
     Read a list of store file names from the standard input, one per line, and write on the standard output the subset of these files missing from the store.

--generate-key[=PARAMETERS]
     Generate a new key pair for the daemon.  This is a prerequisite before archives can be exported with --export.  This operation is usually instantaneous but it can take time if the system's entropy pool needs to be refilled.  On Guix System, guix-service-type takes care of generating this key pair the first boot.

     The generated key pair is typically stored under /etc/guix, in signing-key.pub (public key) and signing-key.sec (private key, which must be kept secret).  When PARAMETERS is omitted, an ECDSA key using the Ed25519 curve is generated, or, for Libgcrypt versions before 1.6.0, it is a 4096-bit RSA key. Alternatively, PARAMETERS can specify genkey parameters suitable for Libgcrypt (see gcry_pk_genkey (The Libgcrypt Reference Manual)).

--authorize
     Authorize imports signed by the public key passed on standard input. The public key must be in ``s-expression advanced format''---i.e., the same format as the signing-key.pub file.

     The list of authorized keys is kept in the human-editable file /etc/guix/acl.  The file contains ``advanced-format s-expressions'' (https://people.csail.mit.edu/rivest/Sexp.txt) and is structured as an access-control list in the Simple Public-Key Infrastructure (SPKI) (https://theworld.com/~cme/spki.txt).

--extract=DIRECTORY
-x DIRECTORY
     Read a single-item archive as served by substitute servers (see Substitutes) and extract it to DIRECTORY.  This is a low-level operation needed in only very narrow use cases; see below.

     For example, the following command extracts the substitute for Emacs served by ci.guix.gnu.org to /tmp/emacs:

          $ wget -O - \
            https://ci.guix.gnu.org/nar/gzip/...-emacs-24.5 \
            | gunzip | guix archive -x /tmp/emacs

     Single-item archives are different from multiple-item archives produced by guix archive --export; they contain a single store item, and they do not embed a signature.  Thus this operation does no signature verification and its output should be considered unsafe.

     The primary purpose of this operation is to facilitate inspection of archive contents coming from possibly untrusted substitute servers (see Invoking guix challenge).

--list
-t
     Read a single-item archive as served by substitute servers (see Substitutes) and print the list of files it contains, as in this example:

          $ wget -O - \
            https://ci.guix.gnu.org/nar/lzip/...-emacs-26.3 \
            | lzip -d | guix archive -t

Channels
********

Guix and its package collection are updated by running guix pull (see Invoking guix pull).  By default guix pull downloads and deploys Guix itself from the official GNU Guix repository.  This can be customized by defining channels in the ~/.config/guix/channels.scm file.  A channel specifies a URL and branch of a Git repository to be deployed, and guix pull can be instructed to pull from one or more channels.  In other words, channels can be used to customize and to extend Guix, as we will see below. Guix is able to take into account security concerns and deal with authenticated updates.

Specifying Additional Channels
==============================

You can specify additional channels to pull from.  To use a channel, write ~/.config/guix/channels.scm to instruct guix pull to pull from it in addition to the default Guix channel(s):

     ;; Add variant packages to those Guix provides.
     (cons (channel
             (name 'variant-packages)
             (url "https://example.org/variant-packages.git"))
           %default-channels)

Note that the snippet above is (as always!) Scheme code; we use cons to add a channel the list of channels that the variable %default-channels is bound to (see cons and lists (GNU Guile Reference Manual)).  With this file in place, guix pull builds not only Guix but also the package modules from your own repository.  The result in ~/.config/guix/current is the union of Guix with your own package modules:

     $ guix describe
     Generation 19	Aug 27 2018 16:20:48
       guix d894ab8
         repository URL: https://git.savannah.gnu.org/git/guix.git
         branch: master
         commit: d894ab8e9bfabcefa6c49d9ba2e834dd5a73a300
       variant-packages dd3df5e
         repository URL: https://example.org/variant-packages.git
         branch: master
         commit: dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb

The output of guix describe above shows that we're now running Generation 19 and that it includes both Guix and packages from the variant-packages channel (see Invoking guix describe).

Using a Custom Guix Channel
===========================

The channel called guix specifies where Guix itself---its command-line tools as well as its package collection---should be downloaded.  For instance, suppose you want to update from another copy of the Guix repository at example.org, and specifically the super-hacks branch, you can write in ~/.config/guix/channels.scm this specification:

     ;; Tell 'guix pull' to use another repo.
     (list (channel
             (name 'guix)
             (url "https://example.org/another-guix.git")
             (branch "super-hacks")))

From there on, guix pull will fetch code from the super-hacks branch of the repository at example.org.  The authentication concern is addressed below (see Channel Authentication).

Note that you can specify a local directory on the url field above if the channel that you intend to use resides on a local file system.  However, in this case guix checks said directory for ownership before any further processing.  This means that if the user is not the directory owner, but wants to use it as their default, they will then need to set it as a safe directory in their global git configuration file.  Otherwise, guix will refuse to even read it.  Supposing your system-wide local directory is at /src/guix.git, you would then create a git configuration file at ~/.gitconfig with the following contents:

     [safe]
             directory = /src/guix.git

This also applies to the root user unless when called with sudo by the directory owner.

Replicating Guix
================

The guix describe command shows precisely which commits were used to build the instance of Guix we're using (see Invoking guix describe).  We can replicate this instance on another machine or at a different point in time by providing a channel specification ``pinned'' to these commits that looks like this:

     ;; Deploy specific commits of my channels of interest.
     (list (channel
            (name 'guix)
            (url "https://git.savannah.gnu.org/git/guix.git")
            (commit "6298c3ffd9654d3231a6f25390b056483e8f407c"))
           (channel
            (name 'variant-packages)
            (url "https://example.org/variant-packages.git")
            (commit "dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb")))

To obtain this pinned channel specification, the easiest way is to run guix describe and to save its output in the channels format in a file, like so:

     guix describe -f channels > channels.scm

The resulting channels.scm file can be passed to the -C option of guix pull (see Invoking guix pull) or guix time-machine (see Invoking guix time-machine), as in this example:

     guix time-machine -C channels.scm -- shell python -- python3

Given the channels.scm file, the command above will always fetch the exact same Guix instance, then use that instance to run the exact same Python (see Invoking guix shell).  On any machine, at any time, it ends up running the exact same binaries, bit for bit.

Pinned channels address a problem similar to ``lock files'' as implemented by some deployment tools---they let you pin and reproduce a set of packages.  In the case of Guix though, you are effectively pinning the entire package set as defined at the given channel commits; in fact, you are pinning all of Guix, including its core modules and command-line tools.  You're also getting strong guarantees that you are, indeed, obtaining the exact same software.

This gives you super powers, allowing you to track the provenance of binary artifacts with very fine grain, and to reproduce software environments at will---some sort of ``meta reproducibility'' capabilities, if you will. See Inferiors, for another way to take advantage of these super powers.

Channel Authentication
======================

The guix pull and guix time-machine commands authenticate the code retrieved from channels: they make sure each commit that is fetched is signed by an authorized developer.  The goal is to protect from unauthorized modifications to the channel that would lead users to run malicious code.

As a user, you must provide a channel introduction in your channels file so that Guix knows how to authenticate its first commit. A channel specification, including its introduction, looks something along these lines:

     (channel
       (name 'some-channel)
       (url "https://example.org/some-channel.git")
       (introduction
        (make-channel-introduction
         "6f0d8cc0d88abb59c324b2990bfee2876016bb86"
         (openpgp-fingerprint
          "CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"))))

The specification above shows the name and URL of the channel.  The call to make-channel-introduction above specifies that authentication of this channel starts at commit 6f0d8cc..., which is signed by the OpenPGP key with fingerprint CABB A931....

For the main channel, called guix, you automatically get that information from your Guix installation.  For other channels, include the channel introduction provided by the channel authors in your channels.scm file.  Make sure you retrieve the channel introduction from a trusted source since that is the root of your trust.

If you're curious about the authentication mechanics, read on!

Channels with Substitutes
=========================

When running guix pull, Guix will first compile the definitions of every available package.  This is an expensive operation for which substitutes (see Substitutes) may be available.  The following snippet in channels.scm will ensure that guix pull uses the latest commit with available substitutes for the package definitions: this is done by querying the continuous integration server at https://ci.guix.gnu.org.

     (use-modules (guix ci))

     (list (channel-with-substitutes-available
            %default-guix-channel
            "https://ci.guix.gnu.org"))

Note that this does not mean that all the packages that you will install after running guix pull will have available substitutes.  It only ensures that guix pull will not try to compile package definitions.  This is particularly useful when using machines with limited resources.

Creating a Channel
==================

Let's say you have a bunch of custom package variants or personal packages that you think would make little sense to contribute to the Guix project, but would like to have these packages transparently available to you at the command line.  By creating a channel, you can use and publish such a package collection.  This involves the following steps:

 1. A channel lives in a Git repository so the first step, when creating a channel, is to create its repository:

          mkdir my-channel
          cd my-channel
          git init

 2. The next step is to create files containing package modules (see Package Modules), each of which will contain one or more package definitions (see Defining Packages).  A channel can provide things other than packages, such as build systems or services; we're using packages as it's the most common use case.

     For example, Alice might want to provide a module called (alice packages greetings) that will provide her favorite ``hello world'' implementations.  To do that Alice will create a directory corresponding to that module name.

          mkdir -p alice/packages
          $EDITOR alice/packages/greetings.scm
          git add alice/packages/greetings.scm

     You can name your package modules however you like; the main constraint to keep in mind is to avoid name clashes with other package collections, which is why our hypothetical Alice wisely chose the (alice packages ...) name space.

     Note that you can also place modules in a sub-directory of the repository; see Package Modules in a Sub-directory, for more info on that.

 3. With this first module in place, the next step is to test the packages it provides.  This can be done with guix build, which needs to be told to look for modules in the Git checkout.  For example, assuming (alice packages greetings) provides a package called hi-from-alice, Alice will run this command from the Git checkout:

          guix build -L. hi-from-alice

     ... where -L. adds the current directory to Guile's load path (see Load Paths (GNU Guile Reference Manual)).

 4. It might take Alice a few iterations to obtain satisfying package definitions.  Eventually Alice will commit this file:

          git commit

     As a channel author, consider bundling authentication material with your channel so that users can authenticate it.  See Channel Authentication, and Specifying Channel Authorizations, for info on how to do it.

 5. To use Alice's channel, anyone can now add it to their channel file (see Specifying Additional Channels) and run guix pull (see Invoking guix pull):

          $EDITOR ~/.config/guix/channels.scm
          guix pull

     Guix will now behave as if the root directory of that channel's Git repository had been permanently added to the Guile load path.  In this example, (alice packages greetings) will automatically be found by the guix command.

Voilà!

     Before you publish your channel, we would like to share a few words of caution:

       * Before publishing a channel, please consider contributing your package definitions to Guix proper (see Contributing).  Guix as a project is open to free software of all sorts, and packages in Guix proper are readily available to all Guix users and benefit from the project's quality assurance process.

       * Package modules and package definitions are Scheme code that uses various programming interfaces (APIs).  We, Guix developers, never change APIs gratuitously, but we do not commit to freezing APIs either.  When you maintain package definitions outside Guix, we consider that the compatibility burden is on you.

       * Corollary: if you're using an external channel and that channel breaks, please report the issue to the channel authors, not to the Guix project.

     You've been warned!  Having said this, we believe external channels are a practical way to exert your freedom to augment Guix' package collection and to share your improvements, which are basic tenets of free software (https://www.gnu.org/philosophy/free-sw.html).  Please email us at guix-devel@gnu.org if you'd like to discuss this.

Package Modules in a Sub-directory
==================================

As a channel author, you may want to keep your channel modules in a sub-directory.  If your modules are in the sub-directory guix, you must add a meta-data file .guix-channel that contains:

     (channel
       (version 0)
       (directory "guix"))

The modules must be underneath the specified directory, as the directory changes Guile's load-path.  For example, if .guix-channel has (directory "base"), then a module defined as (define-module (gnu packages fun)) must be located at base/gnu/packages/fun.scm.

Doing this allows for only parts of a repository to be used as a channel, as Guix expects valid Guile modules when pulling.  For instance, guix deploy machine configuration files are not valid Guile modules, and treating them as such would make guix pull fail.

Declaring Channel Dependencies
==============================

Channel authors may decide to augment a package collection provided by other channels.  They can declare their channel to be dependent on other channels in a meta-data file .guix-channel, which is to be placed in the root of the channel repository.

The meta-data file should contain a simple S-expression like this:

     (channel
      (version 0)
      (dependencies
       (channel
        (name some-collection)
        (url "https://example.org/first-collection.git")

        ;; The 'introduction' bit below is optional: you would
        ;; provide it for dependencies that can be authenticated.
        (introduction
         (channel-introduction
           (version 0)
           (commit "a8883b58dc82e167c96506cf05095f37c2c2c6cd")
           (signer "CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"))))
       (channel
        (name some-other-collection)
        (url "https://example.org/second-collection.git")
        (branch "testing"))))

In the above example this channel is declared to depend on two other channels, which will both be fetched automatically.  The modules provided by the channel will be compiled in an environment where the modules of all these declared channels are available.

For the sake of reliability and maintainability, you should avoid dependencies on channels that you don't control, and you should aim to keep the number of dependencies to a minimum.

Specifying Channel Authorizations
=================================

As we saw above, Guix ensures the source code it pulls from channels comes from authorized developers.  As a channel author, you need to specify the list of authorized developers in the .guix-authorizations file in the channel's Git repository.  The authentication rule is simple: each commit must be signed by a key listed in the .guix-authorizations file of its parent commit(s) (Git commits form a directed acyclic graph (DAG).  Each commit can have zero or more parents; ``regular'' commits have one parent and merge commits have two parent commits.  Read Git for Computer Scientists (https://eagain.net/articles/git-for-computer-scientists/) for a great overview.)  The .guix-authorizations file looks like this:

     ;; Example '.guix-authorizations' file.

     (authorizations
      (version 0)               ;current file format version

      (("AD17 A21E F8AE D8F1 CC02  DBD9 F8AE D8F1 765C 61E3"
        (name "alice"))
       ("2A39 3FFF 68F4 EF7A 3D29  12AF 68F4 EF7A 22FB B2D5"
        (name "bob"))
       ("CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"
        (name "charlie"))))

Each fingerprint is followed by optional key/value pairs, as in the example above.  Currently these key/value pairs are ignored.

This authentication rule creates a chicken-and-egg issue: how do we authenticate the first commit?  Related to that: how do we deal with channels whose repository history contains unsigned commits and lack .guix-authorizations?  And how do we fork existing channels?

Channel introductions answer these questions by describing the first commit of a channel that should be authenticated.  The first time a channel is fetched with guix pull or guix time-machine, the command looks up the introductory commit and verifies that it is signed by the specified OpenPGP key.  From then on, it authenticates commits according to the rule above.  Authentication fails if the target commit is neither a descendant nor an ancestor of the introductory commit.

Additionally, your channel must provide all the OpenPGP keys that were ever mentioned in .guix-authorizations, stored as .key files, which can be either binary or ``ASCII-armored''.  By default, those .key files are searched for in the branch named keyring but you can specify a different branch name in .guix-channel like so:

     (channel
       (version 0)
       (keyring-reference "my-keyring-branch"))

To summarize, as the author of a channel, there are three things you have to do to allow users to authenticate your code:

 1. Export the OpenPGP keys of past and present committers with gpg --export and store them in .key files, by default in a branch named keyring (we recommend making it an orphan branch).

 2. Introduce an initial .guix-authorizations in the channel's repository.  Do that in a signed commit (see Commit Access, for information on how to sign Git commits.)

 3. Advertise the channel introduction, for instance on your channel's web page.  The channel introduction, as we saw above, is the commit/key pair---i.e., the commit that introduced .guix-authorizations, and the fingerprint of the OpenPGP used to sign it.

Before pushing to your public Git repository, you can run guix git authenticate to verify that you did sign all the commits you are about to push with an authorized key:

     guix git authenticate COMMIT SIGNER

where COMMIT and SIGNER are your channel introduction. See Invoking guix git authenticate, for details.

Publishing a signed channel requires discipline: any mistake, such as an unsigned commit or a commit signed by an unauthorized key, will prevent users from pulling from your channel---well, that's the whole point of authentication!  Pay attention to merges in particular: merge commits are considered authentic if and only if they are signed by a key present in the .guix-authorizations file of both branches.

Primary URL
===========

Channel authors can indicate the primary URL of their channel's Git repository in the .guix-channel file, like so:

     (channel
       (version 0)
       (url "https://example.org/guix.git"))

This allows guix pull to determine whether it is pulling code from a mirror of the channel; when that is the case, it warns the user that the mirror might be stale and displays the primary URL.  That way, users cannot be tricked into fetching code from a stale mirror that does not receive security updates.

This feature only makes sense for authenticated repositories, such as the official guix channel, for which guix pull ensures the code it fetches is authentic.

Writing Channel News
====================

Channel authors may occasionally want to communicate to their users information about important changes in the channel.  You'd send them all an email, but that's not convenient.

Instead, channels can provide a news file; when the channel users run guix pull, that news file is automatically read and guix pull --news can display the announcements that correspond to the new commits that have been pulled, if any.

To do that, channel authors must first declare the name of the news file in their .guix-channel file:

     (channel
       (version 0)
       (news-file "etc/news.txt"))

The news file itself, etc/news.txt in this example, must look something like this:

     (channel-news
       (version 0)
       (entry (tag "the-bug-fix")
              (title (en "Fixed terrible bug")
                     (fr "Oh la la"))
              (body (en "@emph{Good news}!  It's fixed!")
                    (eo "Certe ĝi pli bone funkcias nun!")))
       (entry (commit "bdcabe815cd28144a2d2b4bc3c5057b051fa9906")
              (title (en "Added a great package")
                     (ca "Què vol dir guix?"))
              (body (en "Don't miss the @code{hello} package!"))))

While the news file is using the Scheme syntax, avoid naming it with a .scm extension or else it will get picked up when building the channel and yield an error since it is not a valid module. Alternatively, you can move the channel module to a subdirectory and store the news file in another directory.

The file consists of a list of news entries.  Each entry is associated with a commit or tag: it describes changes made in this commit, possibly in preceding commits as well.  Users see entries only the first time they obtain the commit the entry refers to.

The title field should be a one-line summary while body can be arbitrarily long, and both can contain Texinfo markup (see Overview (GNU Texinfo)).  Both the title and body are a list of language tag/message tuples, which allows guix pull to display news in the language that corresponds to the user's locale.

If you want to translate news using a gettext-based workflow, you can extract translatable strings with xgettext (see xgettext Invocation (GNU Gettext Utilities)).  For example, assuming you write news entries in English first, the command below creates a PO file containing the strings to translate:

     xgettext -o news.po -l scheme -ken etc/news.txt

To sum up, yes, you could use your channel as a blog.  But beware, this is not quite what your users might expect.

Development
***********

If you are a software developer, Guix provides tools that you should find helpful---independently of the language you're developing in.  This is what this chapter is about.

The guix shell command provides a convenient way to set up one-off software environments, be it for development purposes or to run a command without installing it in your profile.  The guix pack command allows you to create application bundles that can be easily distributed to users who do not run Guix.

Invoking guix shell
===================

The purpose of guix shell is to make it easy to create one-off software environments, without changing one's profile.  It is typically used to create development environments; it is also a convenient way to run applications without ``polluting'' your profile.

     The guix shell command was recently introduced to supersede guix environment (see Invoking guix environment).  If you are familiar with guix environment, you will notice that it is similar but also---we hope!---more convenient.

The general syntax is:

     guix shell [OPTIONS] [PACKAGE...]

The following example creates an environment containing Python and NumPy, building or downloading any missing package, and runs the python3 command in that environment:

     guix shell python python-numpy -- python3

Note that it is necessary to include the main python package in this command even if it is already installed into your environment. This is so that the shell environment knows to set PYTHONPATH and other related variables.  The shell environment cannot check the previously installed environment, because then it would be non-deterministic.  This is true for most libraries: their corresponding language package should be included in the shell invocation.

     guix shell can be also be used as a script interpreter, also known as shebang.  Here is an example self-contained Python script making use of this feature:

          #!/usr/bin/env -S guix shell python python-numpy -- python3
          import numpy
          print("This is numpy", numpy.version.version)

     You may pass any guix shell option, but there's one caveat: the Linux kernel has a limit of 127 bytes on shebang length.

Development environments can be created as in the example below, which spawns an interactive shell containing all the dependencies and environment variables needed to work on Inkscape:

     guix shell --development inkscape

Exiting the shell places the user back in the original environment before guix shell was invoked.  The next garbage collection (see Invoking guix gc) may clean up packages that were installed in the environment and that are no longer used outside of it.

As an added convenience, guix shell will try to do what you mean when it is invoked interactively without any other arguments as in:

     guix shell

If it finds a manifest.scm in the current working directory or any of its parents, it uses this manifest as though it was given via --manifest. Likewise, if it finds a guix.scm in the same directories, it uses it to build a development profile as though both --development and --file were present. In either case, the file will only be loaded if the directory it resides in is listed in ~/.config/guix/shell-authorized-directories. This provides an easy way to define, share, and enter development environments.

By default, the shell session or command runs in an augmented environment, where the new packages are added to search path environment variables such as PATH.  You can, instead, choose to create an isolated environment containing nothing but the packages you asked for.  Passing the --pure option clears environment variable definitions found in the parent environment (Be sure to use the --check option the first time you use guix shell interactively to make sure the shell does not undo the effect of --pure.); passing --container goes one step further by spawning a container isolated from the rest of the system:

     guix shell --container emacs gcc-toolchain

The command above spawns an interactive shell in a container where nothing but emacs, gcc-toolchain, and their dependencies is available.  The container lacks network access and shares no files other than the current working directory with the surrounding environment.  This is useful to prevent access to system-wide resources such as /usr/bin on foreign distros.

This --container option can also prove useful if you wish to run a security-sensitive application, such as a web browser, in an isolated environment.  For example, the command below launches Ungoogled-Chromium in an isolated environment, this time sharing network access with the host and preserving its DISPLAY environment variable, but without even sharing the current directory:

     guix shell --container --network --no-cwd ungoogled-chromium \
       --preserve='^DISPLAY$' -- chromium

guix shell defines the GUIX_ENVIRONMENT variable in the shell it spawns; its value is the file name of the profile of this environment.  This allows users to, say, define a specific prompt for development environments in their .bashrc (see Bash Startup Files (The GNU Bash Reference Manual)):

     if [ -n "$GUIX_ENVIRONMENT" ]
     then
         export PS1="\u@\h \w [dev]\$ "
     fi

... or to browse the profile:

     $ ls "$GUIX_ENVIRONMENT/bin"

The available options are summarized below.

--check
     Set up the environment and check whether the shell would clobber environment variables.  It's a good idea to use this option the first time you run guix shell for an interactive session to make sure your setup is correct.

     For example, if the shell modifies the PATH environment variable, report it since you would get a different environment than what you asked for.

     Such problems usually indicate that the shell startup files are unexpectedly modifying those environment variables.  For example, if you are using Bash, make sure that environment variables are set or modified in ~/.bash_profile and not in ~/.bashrc---the former is sourced only by log-in shells.  See Bash Startup Files (The GNU Bash Reference Manual), for details on Bash start-up files.

--development
-D
     Cause guix shell to include in the environment the dependencies of the following package rather than the package itself. This can be combined with other packages.  For instance, the command below starts an interactive shell containing the build-time dependencies of GNU Guile, plus Autoconf, Automake, and Libtool:

          guix shell -D guile autoconf automake libtool

--expression=EXPR
-e EXPR
     Create an environment for the package or list of packages that EXPR evaluates to.

     For example, running:

          guix shell -D -e '(@ (gnu packages maths) petsc-openmpi)'

     starts a shell with the environment for this specific variant of the PETSc package.

     Running:

          guix shell -e '(@ (gnu) %base-packages)'

     starts a shell with all the base system packages available.

     The above commands only use the default output of the given packages. To select other outputs, two element tuples can be specified:

          guix shell -e '(list (@ (gnu packages bash) bash) "include")'

     See package->development-manifest, for information on how to write a manifest for the development environment of a package.

--file=FILE
-f FILE
     Create an environment containing the package or list of packages that the code within FILE evaluates to.

     As an example, FILE might contain a definition like this (see Defining Packages):

               [file environment-gdb.scm not included]

     With the file above, you can enter a development environment for GDB by running:

          guix shell -D -f gdb-devel.scm

--manifest=FILE
-m FILE
     Create an environment for the packages contained in the manifest object returned by the Scheme code in FILE.  This option can be repeated several times, in which case the manifests are concatenated.

     This is similar to the same-named option in guix package (see --manifest) and uses the same manifest files.

     See Writing Manifests, for information on how to write a manifest. See --export-manifest below on how to obtain a first manifest.

--export-manifest
     Write to standard output a manifest suitable for --manifest corresponding to given command-line options.

     This is a way to ``convert'' command-line arguments into a manifest. For example, imagine you are tired of typing long lines and would like to get a manifest equivalent to this command line:

          guix shell -D guile git emacs emacs-geiser emacs-geiser-guile

     Just add --export-manifest to the command line above:

          guix shell --export-manifest \
            -D guile git emacs emacs-geiser emacs-geiser-guile

     ... and you get a manifest along these lines:

          (concatenate-manifests
            (list (specifications->manifest
                    (list "git"
                          "emacs"
                          "emacs-geiser"
                          "emacs-geiser-guile"))
                  (package->development-manifest
                    (specification->package "guile"))))

     You can store it into a file, say manifest.scm, and from there pass it to guix shell or indeed pretty much any guix command:

          guix shell -m manifest.scm

     Voilà, you've converted a long command line into a manifest!  That conversion process honors package transformation options (see Package Transformation Options) so it should be lossless.

--profile=PROFILE
-p PROFILE
     Create an environment containing the packages installed in PROFILE. Use guix package (see Invoking guix package) to create and manage profiles.

--pure
     Unset existing environment variables when building the new environment, except those specified with --preserve (see below).  This has the effect of creating an environment in which search paths only contain package inputs.

--preserve=REGEXP
-E REGEXP
     When used alongside --pure, preserve the environment variables matching REGEXP---in other words, put them on a ``white list'' of environment variables that must be preserved.  This option can be repeated several times.

          guix shell --pure --preserve=^SLURM openmpi ... \
            -- mpirun ...

     This example runs mpirun in a context where the only environment variables defined are PATH, environment variables whose name starts with SLURM, as well as the usual ``precious'' variables (HOME, USER, etc.).

--search-paths
     Display the environment variable definitions that make up the environment.

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., i686-linux.

--container
-C
     Run COMMAND within an isolated container.  The current working directory outside the container is mapped inside the container. Additionally, unless overridden with --user, a dummy home directory is created that matches the current user's home directory, and /etc/passwd is configured accordingly.

     The spawned process runs as the current user outside the container.  Inside the container, it has the same UID and GID as the current user, unless --user is passed (see below).

--network
-N
     For containers, share the network namespace with the host system. Containers created without this flag only have access to the loopback device.

--link-profile
-P
     For containers, link the environment profile to ~/.guix-profile within the container and set GUIX_ENVIRONMENT to that. This is equivalent to making ~/.guix-profile a symlink to the actual profile within the container. Linking will fail and abort the environment if the directory already exists, which will certainly be the case if guix shell was invoked in the user's home directory.

     Certain packages are configured to look in ~/.guix-profile for configuration files and data; (For example, the fontconfig package inspects ~/.guix-profile/share/fonts for additional fonts.)  --link-profile allows these programs to behave as expected within the environment.

--user=USER
-u USER
     For containers, use the username USER in place of the current user.  The generated /etc/passwd entry within the container will contain the name USER, the home directory will be /home/USER, and no user GECOS data will be copied.  Furthermore, the UID and GID inside the container are 1000.  USER need not exist on the system.

     Additionally, any shared or exposed path (see --share and --expose respectively) whose target is within the current user's home directory will be remapped relative to /home/USER; this includes the automatic mapping of the current working directory.

          # will expose paths as /home/foo/wd, /home/foo/test, and /home/foo/target
          cd $HOME/wd
          guix shell --container --user=foo \
               --expose=$HOME/test \
               --expose=/tmp/target=$HOME/target

     While this will limit the leaking of user identity through home paths and each of the user fields, this is only one useful component of a broader privacy/anonymity solution---not one in and of itself.

--no-cwd
     For containers, the default behavior is to share the current working directory with the isolated container and immediately change to that directory within the container.  If this is undesirable, --no-cwd will cause the current working directory to not be automatically shared and will change to the user's home directory within the container instead.  See also --user.

--expose=SOURCE[=TARGET]
--share=SOURCE[=TARGET]
     For containers, --expose (resp. --share) exposes the file system SOURCE from the host system as the read-only (resp. writable) file system TARGET within the container.  If TARGET is not specified, SOURCE is used as the target mount point in the container.

     The example below spawns a Guile REPL in a container in which the user's home directory is accessible read-only via the /exchange directory:

          guix shell --container --expose=$HOME=/exchange guile -- guile

--symlink=SPEC
-S SPEC
     For containers, create the symbolic links specified by SPEC, as documented in pack-symlink-option.

--emulate-fhs
-F
     When used with --container, emulate a Filesystem Hierarchy Standard (FHS) (https://refspecs.linuxfoundation.org/fhs.shtml) configuration within the container, providing /bin, /lib, and other directories and files specified by the FHS.

     As Guix deviates from the FHS specification, this option sets up the container to more closely mimic that of other GNU/Linux distributions.  This is useful for reproducing other development environments, testing, and using programs which expect the FHS specification to be followed.  With this option, the container will include a version of glibc that will read /etc/ld.so.cache within the container for the shared library cache (contrary to glibc in regular Guix usage) and set up the expected FHS directories: /bin, /etc, /lib, and /usr from the container's profile.

--nesting
-W
     When used with --container, provide Guix inside the container and arrange so that it can interact with the build daemon that runs outside the container.  This is useful if you want, within your isolated container, to create other containers, as in this sample session:

          $ guix shell -CW coreutils
          [env]$ guix shell -C guile -- guile -c '(display "hello!\n")'
          hello!
          [env]$ exit

     The session above starts a container with coreutils programs available in PATH.  From there, we spawn guix shell to create a nested container that provides nothing but Guile.

     Another example is evaluating a guix.scm file that is untrusted, as shown here:

          guix shell -CW -- guix build -f guix.scm

     The guix build command as executed above can only access the current directory.

     Under the hood, the -W option does several things:

       * map the daemon's socket (by default /var/guix/daemon-socket/socket) inside the container;

       * map the whole store (by default /gnu/store) inside the container such that store items made available by nested guix invocations are visible;

       * add the currently-used guix command to the profile in the container, such that guix describe returns the same state inside and outside the container;

       * share the cache (by default ~/.cache/guix) with the host, to speed up operations such as guix time-machine and guix shell.

--rebuild-cache
     In most cases, guix shell caches the environment so that subsequent uses are instantaneous.  Least-recently used cache entries are periodically removed.  The cache is also invalidated, when using --file or --manifest, anytime the corresponding file is modified.

     The --rebuild-cache forces the cached environment to be refreshed.  This is useful when using --file or --manifest and the guix.scm or manifest.scm file has external dependencies, or if its behavior depends, say, on environment variables.

--root=FILE
-r FILE
     Make FILE a symlink to the profile for this environment, and register it as a garbage collector root.

     This is useful if you want to protect your environment from garbage collection, to make it ``persistent''.

     When this option is omitted, guix shell caches profiles so that subsequent uses of the same environment are instantaneous---this is comparable to using --root except that guix shell takes care of periodically removing the least-recently used garbage collector roots.

     In some cases, guix shell does not cache profiles---e.g., if transformation options such as --with-latest are used.  In those cases, the environment is protected from garbage collection only for the duration of the guix shell session.  This means that next time you recreate the same environment, you could have to rebuild or re-download packages.

     See Invoking guix gc, for more on GC roots.

guix shell also supports all of the common build options that guix build supports (see Common Build Options) as well as package transformation options (see Package Transformation Options).

Invoking guix environment
=========================

The purpose of guix environment is to assist in creating development environments.

     The guix environment command is deprecated in favor of guix shell, which performs similar functions but is more convenient to use.  See Invoking guix shell.

     Being deprecated, guix environment is slated for eventual removal, but the Guix project is committed to keeping it until May 1st, 2023.  Please get in touch with us at guix-devel@gnu.org if you would like to discuss it.

The general syntax is:

     guix environment OPTIONS PACKAGE...

The following example spawns a new shell set up for the development of GNU Guile:

     guix environment guile

If the needed dependencies are not built yet, guix environment automatically builds them.  The environment of the new shell is an augmented version of the environment that guix environment was run in.  It contains the necessary search paths for building the given package added to the existing environment variables.  To create a ``pure'' environment, in which the original environment variables have been unset, use the --pure option (Users sometimes wrongfully augment environment variables such as PATH in their ~/.bashrc file.  As a consequence, when guix environment launches it, Bash may read ~/.bashrc, thereby introducing ``impurities'' in these environment variables.  It is an error to define such environment variables in .bashrc; instead, they should be defined in .bash_profile, which is sourced only by log-in shells.  See Bash Startup Files (The GNU Bash Reference Manual), for details on Bash start-up files.).

Exiting from a Guix environment is the same as exiting from the shell, and will place the user back in the old environment before guix environment was invoked.  The next garbage collection (see Invoking guix gc) will clean up packages that were installed from within the environment and are no longer used outside of it.

guix environment defines the GUIX_ENVIRONMENT variable in the shell it spawns; its value is the file name of the profile of this environment.  This allows users to, say, define a specific prompt for development environments in their .bashrc (see Bash Startup Files (The GNU Bash Reference Manual)):

     if [ -n "$GUIX_ENVIRONMENT" ]
     then
         export PS1="\u@\h \w [dev]\$ "
     fi

... or to browse the profile:

     $ ls "$GUIX_ENVIRONMENT/bin"

Additionally, more than one package may be specified, in which case the union of the inputs for the given packages are used.  For example, the command below spawns a shell where all of the dependencies of both Guile and Emacs are available:

     guix environment guile emacs

Sometimes an interactive shell session is not desired.  An arbitrary command may be invoked by placing the -- token to separate the command from the rest of the arguments:

     guix environment guile -- make -j4

In other situations, it is more convenient to specify the list of packages needed in the environment.  For example, the following command runs python from an environment containing Python 3 and NumPy:

     guix environment --ad-hoc python-numpy python -- python3

Furthermore, one might want the dependencies of a package and also some additional packages that are not build-time or runtime dependencies, but are useful when developing nonetheless.  Because of this, the --ad-hoc flag is positional.  Packages appearing before --ad-hoc are interpreted as packages whose dependencies will be added to the environment.  Packages appearing after are interpreted as packages that will be added to the environment directly.  For example, the following command creates a Guix development environment that additionally includes Git and strace:

     guix environment --pure guix --ad-hoc git strace

Sometimes it is desirable to isolate the environment as much as possible, for maximal purity and reproducibility.  In particular, when using Guix on a host distro that is not Guix System, it is desirable to prevent access to /usr/bin and other system-wide resources from the development environment.  For example, the following command spawns a Guile REPL in a ``container'' where only the store and the current working directory are mounted:

     guix environment --ad-hoc --container guile -- guile

     The --container option requires Linux-libre 3.19 or newer.

Another typical use case for containers is to run security-sensitive applications such as a web browser.  To run Eolie, we must expose and share some files and directories; we include nss-certs and expose /etc/ssl/certs/ for HTTPS authentication; finally we preserve the DISPLAY environment variable since containerized graphical applications won't display without it.

     guix environment --preserve='^DISPLAY$' --container --network \
       --expose=/etc/machine-id \
       --expose=/etc/ssl/certs/ \
       --share=$HOME/.local/share/eolie/=$HOME/.local/share/eolie/ \
       --ad-hoc eolie nss-certs dbus --  eolie

The available options are summarized below.

--check
     Set up the environment and check whether the shell would clobber environment variables.  See --check, for more info.

--root=FILE
-r FILE
     Make FILE a symlink to the profile for this environment, and register it as a garbage collector root.

     This is useful if you want to protect your environment from garbage collection, to make it ``persistent''.

     When this option is omitted, the environment is protected from garbage collection only for the duration of the guix environment session.  This means that next time you recreate the same environment, you could have to rebuild or re-download packages.  See Invoking guix gc, for more on GC roots.

--expression=EXPR
-e EXPR
     Create an environment for the package or list of packages that EXPR evaluates to.

     For example, running:

          guix environment -e '(@ (gnu packages maths) petsc-openmpi)'

     starts a shell with the environment for this specific variant of the PETSc package.

     Running:

          guix environment --ad-hoc -e '(@ (gnu) %base-packages)'

     starts a shell with all the base system packages available.

     The above commands only use the default output of the given packages. To select other outputs, two element tuples can be specified:

          guix environment --ad-hoc -e '(list (@ (gnu packages bash) bash) "include")'

--load=FILE
-l FILE
     Create an environment for the package or list of packages that the code within FILE evaluates to.

     As an example, FILE might contain a definition like this (see Defining Packages):

               [file environment-gdb.scm not included]

--manifest=FILE
-m FILE
     Create an environment for the packages contained in the manifest object returned by the Scheme code in FILE.  This option can be repeated several times, in which case the manifests are concatenated.

     This is similar to the same-named option in guix package (see --manifest) and uses the same manifest files.

     See guix shell --export-manifest, for information on how to ``convert'' command-line options into a manifest.

--ad-hoc
     Include all specified packages in the resulting environment, as if an ad hoc package were defined with them as inputs.  This option is useful for quickly creating an environment without having to write a package expression to contain the desired inputs.

     For instance, the command:

          guix environment --ad-hoc guile guile-sdl -- guile

     runs guile in an environment where Guile and Guile-SDL are available.

     Note that this example implicitly asks for the default output of guile and guile-sdl, but it is possible to ask for a specific output---e.g., glib:bin asks for the bin output of glib (see Packages with Multiple Outputs).

     This option may be composed with the default behavior of guix environment.  Packages appearing before --ad-hoc are interpreted as packages whose dependencies will be added to the environment, the default behavior.  Packages appearing after are interpreted as packages that will be added to the environment directly.

--profile=PROFILE
-p PROFILE
     Create an environment containing the packages installed in PROFILE. Use guix package (see Invoking guix package) to create and manage profiles.

--pure
     Unset existing environment variables when building the new environment, except those specified with --preserve (see below).  This has the effect of creating an environment in which search paths only contain package inputs.

--preserve=REGEXP
-E REGEXP
     When used alongside --pure, preserve the environment variables matching REGEXP---in other words, put them on a ``white list'' of environment variables that must be preserved.  This option can be repeated several times.

          guix environment --pure --preserve=^SLURM --ad-hoc openmpi ... \
            -- mpirun ...

     This example runs mpirun in a context where the only environment variables defined are PATH, environment variables whose name starts with SLURM, as well as the usual ``precious'' variables (HOME, USER, etc.).

--search-paths
     Display the environment variable definitions that make up the environment.

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., i686-linux.

--container
-C
     Run COMMAND within an isolated container.  The current working directory outside the container is mapped inside the container. Additionally, unless overridden with --user, a dummy home directory is created that matches the current user's home directory, and /etc/passwd is configured accordingly.

     The spawned process runs as the current user outside the container.  Inside the container, it has the same UID and GID as the current user, unless --user is passed (see below).

--network
-N
     For containers, share the network namespace with the host system. Containers created without this flag only have access to the loopback device.

--link-profile
-P
     For containers, link the environment profile to ~/.guix-profile within the container and set GUIX_ENVIRONMENT to that. This is equivalent to making ~/.guix-profile a symlink to the actual profile within the container. Linking will fail and abort the environment if the directory already exists, which will certainly be the case if guix environment was invoked in the user's home directory.

     Certain packages are configured to look in ~/.guix-profile for configuration files and data; (For example, the fontconfig package inspects ~/.guix-profile/share/fonts for additional fonts.)  --link-profile allows these programs to behave as expected within the environment.

--user=USER
-u USER
     For containers, use the username USER in place of the current user.  The generated /etc/passwd entry within the container will contain the name USER, the home directory will be /home/USER, and no user GECOS data will be copied.  Furthermore, the UID and GID inside the container are 1000.  USER need not exist on the system.

     Additionally, any shared or exposed path (see --share and --expose respectively) whose target is within the current user's home directory will be remapped relative to /home/USER; this includes the automatic mapping of the current working directory.

          # will expose paths as /home/foo/wd, /home/foo/test, and /home/foo/target
          cd $HOME/wd
          guix environment --container --user=foo \
               --expose=$HOME/test \
               --expose=/tmp/target=$HOME/target

     While this will limit the leaking of user identity through home paths and each of the user fields, this is only one useful component of a broader privacy/anonymity solution---not one in and of itself.

--no-cwd
     For containers, the default behavior is to share the current working directory with the isolated container and immediately change to that directory within the container.  If this is undesirable, --no-cwd will cause the current working directory to not be automatically shared and will change to the user's home directory within the container instead.  See also --user.

--expose=SOURCE[=TARGET]
--share=SOURCE[=TARGET]
     For containers, --expose (resp. --share) exposes the file system SOURCE from the host system as the read-only (resp. writable) file system TARGET within the container.  If TARGET is not specified, SOURCE is used as the target mount point in the container.

     The example below spawns a Guile REPL in a container in which the user's home directory is accessible read-only via the /exchange directory:

          guix environment --container --expose=$HOME=/exchange --ad-hoc guile -- guile

--emulate-fhs

-F
     For containers, emulate a Filesystem Hierarchy Standard (FHS) configuration within the container, see the official specification (https://refspecs.linuxfoundation.org/fhs.shtml).  As Guix deviates from the FHS specification, this option sets up the container to more closely mimic that of other GNU/Linux distributions.  This is useful for reproducing other development environments, testing, and using programs which expect the FHS specification to be followed.  With this option, the container will include a version of glibc which will read /etc/ld.so.cache within the container for the shared library cache (contrary to glibc in regular Guix usage) and set up the expected FHS directories: /bin, /etc, /lib, and /usr from the container's profile.

guix environment also supports all of the common build options that guix build supports (see Common Build Options) as well as package transformation options (see Package Transformation Options).

Invoking guix pack
==================

Occasionally you want to pass software to people who are not (yet!) lucky enough to be using Guix.  You'd tell them to run guix package -i SOMETHING, but that's not possible in this case.  This is where guix pack comes in.

     If you are looking for ways to exchange binaries among machines that already run Guix, see Invoking guix copy, Invoking guix publish, and Invoking guix archive.

The guix pack command creates a shrink-wrapped pack or software bundle: it creates a tarball or some other archive containing the binaries of the software you're interested in, and all its dependencies.  The resulting archive can be used on any machine that does not have Guix, and people can run the exact same binaries as those you have with Guix.  The pack itself is created in a bit-reproducible fashion, so anyone can verify that it really contains the build results that you pretend to be shipping.

For example, to create a bundle containing Guile, Emacs, Geiser, and all their dependencies, you can run:

     $ guix pack guile emacs emacs-geiser
     ...
     /gnu/store/...-pack.tar.gz

The result here is a tarball containing a /gnu/store directory with all the relevant packages.  The resulting tarball contains a profile with the three packages of interest; the profile is the same as would be created by guix package -i.  It is this mechanism that is used to create Guix's own standalone binary tarball (see Binary Installation).

Users of this pack would have to run /gnu/store/...-profile/bin/guile to run Guile, which you may find inconvenient.  To work around it, you can create, say, a /opt/gnu/bin symlink to the profile:

     guix pack -S /opt/gnu/bin=bin guile emacs emacs-geiser

That way, users can happily type /opt/gnu/bin/guile and enjoy.

What if the recipient of your pack does not have root privileges on their machine, and thus cannot unpack it in the root file system?  In that case, you will want to use the --relocatable option (see below).  This option produces relocatable binaries, meaning they can be placed anywhere in the file system hierarchy: in the example above, users can unpack your tarball in their home directory and directly run ./opt/gnu/bin/guile.

Alternatively, you can produce a pack in the Docker image format using the following command:

     guix pack -f docker -S /bin=bin guile guile-readline

The result is a tarball that can be passed to the docker load command, followed by docker run:

     docker load < FILE
     docker run -ti guile-guile-readline /bin/guile

where FILE is the image returned by guix pack, and guile-guile-readline is its ``image tag''.  See the Docker documentation (https://docs.docker.com/engine/reference/commandline/load/) for more information.

Yet another option is to produce a SquashFS image with the following command:

     guix pack -f squashfs bash guile emacs emacs-geiser

The result is a SquashFS file system image that can either be mounted or directly be used as a file system container image with the Singularity container execution environment (https://www.sylabs.io/docs/), using commands like singularity shell or singularity exec.

Several command-line options allow you to customize your pack:

--format=FORMAT
-f FORMAT
     Produce a pack in the given FORMAT.

     The available formats are:

     tarball
          This is the default format.  It produces a tarball containing all the specified binaries and symlinks.

     docker
          This produces a tarball that follows the Docker Image Specification (https://github.com/docker/docker/blob/master/image/spec/v1.2.md).  By default, the ``repository name'' as it appears in the output of the docker images command is computed from package names passed on the command line or in the manifest file. Alternatively, the ``repository name'' can also be configured via the --image-tag option.  Refer to --help-docker-format for more information on such advanced options.

     squashfs
          This produces a SquashFS image containing all the specified binaries and symlinks, as well as empty mount points for virtual file systems like procfs.

               Singularity requires you to provide /bin/sh in the image. For that reason, guix pack -f squashfs always implies -S /bin=bin.  Thus, your guix pack invocation must always start with something like:

                    guix pack -f squashfs bash ...

               If you forget the bash (or similar) package, singularity run and singularity exec will fail with an unhelpful ``no such file or directory'' message.

     deb
          This produces a Debian archive (a package with the .deb file extension) containing all the specified binaries and symbolic links, that can be installed on top of any dpkg-based GNU(/Linux) distribution. Advanced options can be revealed via the --help-deb-format option.  They allow embedding control files for more fine-grained control, such as activating specific triggers or providing a maintainer configure script to run arbitrary setup code upon installation.

               guix pack -f deb -C xz -S /usr/bin/hello=bin/hello hello

               Because archives produced with guix pack contain a collection of store items and because each dpkg package must not have conflicting files, in practice that means you likely won't be able to install more than one such archive on a given system.  You can nonetheless pack as many Guix packages as you want in one such archive.

               dpkg will assume ownership of any files contained in the pack that it does not know about.  It is unwise to install Guix-produced .deb files on a system where /gnu/store is shared by other software, such as a Guix installation or other, non-deb packs.

     rpm
          This produces an RPM archive (a package with the .rpm file extension) containing all the specified binaries and symbolic links, that can be installed on top of any RPM-based GNU/Linux distribution. The RPM format embeds checksums for every file it contains, which the rpm command uses to validate the integrity of the archive.

          Advanced RPM-related options are revealed via the --help-rpm-format option.  These options allow embedding maintainer scripts that can run before or after the installation of the RPM archive, for example.

          The RPM format supports relocatable packages via the --prefix option of the rpm command, which can be handy to install an RPM package to a specific prefix.

               guix pack -f rpm -R -C xz -S /usr/bin/hello=bin/hello hello

               sudo rpm --install --prefix=/opt /gnu/store/...-hello.rpm

               Contrary to Debian packages, conflicting but identical files in RPM packages can be installed simultaneously, which means multiple guix pack-produced RPM packages can usually be installed side by side without any problem.

               rpm assumes ownership of any files contained in the pack, which means it will remove /gnu/store upon uninstalling a Guix-generated RPM package, unless the RPM package was installed with the --prefix option of the rpm command.  It is unwise to install Guix-produced .rpm packages on a system where /gnu/store is shared by other software, such as a Guix installation or other, non-rpm packs.

--relocatable
-R
     Produce relocatable binaries---i.e., binaries that can be placed anywhere in the file system hierarchy and run from there.

     When this option is passed once, the resulting binaries require support for user namespaces in the kernel Linux; when passed twice (Here's a trick to memorize it: -RR, which adds PRoot support, can be thought of as the abbreviation of ``Really Relocatable''.  Neat, isn't it?), relocatable binaries fall to back to other techniques if user namespaces are unavailable, and essentially work anywhere---see below for the implications.

     For example, if you create a pack containing Bash with:

          guix pack -RR -S /mybin=bin bash

     ... you can copy that pack to a machine that lacks Guix, and from your home directory as a normal user, run:

          tar xf pack.tar.gz
          ./mybin/sh

     In that shell, if you type ls /gnu/store, you'll notice that /gnu/store shows up and contains all the dependencies of bash, even though the machine actually lacks /gnu/store altogether!  That is probably the simplest way to deploy Guix-built software on a non-Guix machine.

          By default, relocatable binaries rely on the user namespace feature of the kernel Linux, which allows unprivileged users to mount or change root. Old versions of Linux did not support it, and some GNU/Linux distributions turn it off.

          To produce relocatable binaries that work even in the absence of user namespaces, pass --relocatable or -R twice.  In that case, binaries will try user namespace support and fall back to another execution engine if user namespaces are not supported.  The following execution engines are supported:

          default
               Try user namespaces and fall back to PRoot if user namespaces are not supported (see below).

          performance
               Try user namespaces and fall back to Fakechroot if user namespaces are not supported (see below).

          userns
               Run the program through user namespaces and abort if they are not supported.

          proot
               Run through PRoot.  The PRoot (https://proot-me.github.io/) program provides the necessary support for file system virtualization.  It achieves that by using the ptrace system call on the running program.  This approach has the advantage to work without requiring special kernel support, but it incurs run-time overhead every time a system call is made.

          fakechroot
               Run through Fakechroot.  Fakechroot (https://github.com/dex4er/fakechroot/) virtualizes file system accesses by intercepting calls to C library functions such as open, stat, exec, and so on.  Unlike PRoot, it incurs very little overhead.  However, it does not always work: for example, some file system accesses made from within the C library are not intercepted, and file system accesses made via direct syscalls are not intercepted either, leading to erratic behavior.

          When running a wrapped program, you can explicitly request one of the execution engines listed above by setting the GUIX_EXECUTION_ENGINE environment variable accordingly.

--entry-point=COMMAND
     Use COMMAND as the entry point of the resulting pack, if the pack format supports it---currently docker and squashfs (Singularity) support it.  COMMAND must be relative to the profile contained in the pack.

     The entry point specifies the command that tools like docker run or singularity run automatically start by default.  For example, you can do:

          guix pack -f docker --entry-point=bin/guile guile

     The resulting pack can easily be loaded and docker run with no extra arguments will spawn bin/guile:

          docker load -i pack.tar.gz
          docker run IMAGE-ID

--entry-point-argument=COMMAND
-A COMMAND
     Use COMMAND as an argument to entry point of the resulting pack. This option is only valid in conjunction with --entry-point and can appear multiple times on the command line.

          guix pack -f docker --entry-point=bin/guile --entry-point-argument="--help" guile

--max-layers=n
     Specifies the maximum number of Docker image layers allowed when building an image.

          guix pack -f docker --max-layers=100 guile

     This option allows you to limit the number of layers in a Docker image. Docker images are comprised of multiple layers, and each layer adds to the overall size and complexity of the image.  By setting a maximum number of layers, you can control the following effects:

       * Disk Usage: Increasing the number of layers can help optimize the disk space required to store multiple images built with a similar package graph.

       * Pulling: When transferring images between different nodes or systems, having more layers can reduce the time required to pull the image.

--expression=EXPR
-e EXPR
     Consider the package EXPR evaluates to.

     This has the same purpose as the same-named option in guix build (see --expression in guix build).

--manifest=FILE
-m FILE
     Use the packages contained in the manifest object returned by the Scheme code in FILE.  This option can be repeated several times, in which case the manifests are concatenated.

     This has a similar purpose as the same-named option in guix package (see --manifest) and uses the same manifest files.  It allows you to define a collection of packages once and use it both for creating profiles and for creating archives for use on machines that do not have Guix installed.  Note that you can specify either a manifest file or a list of packages, but not both.

     See Writing Manifests, for information on how to write a manifest. See guix shell --export-manifest, for information on how to ``convert'' command-line options into a manifest.

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., i686-linux---instead of the system type of the build host.

--target=TRIPLET
     Cross-build for TRIPLET, which must be a valid GNU triplet, such as "aarch64-linux-gnu" (see GNU configuration triplets (Autoconf)).

--compression=TOOL
-C TOOL
     Compress the resulting tarball using TOOL---one of gzip, zstd, bzip2, xz, lzip, or none for no compression.

--symlink=SPEC
-S SPEC
     Add the symlinks specified by SPEC to the pack.  This option can appear several times.

     SPEC has the form SOURCE=TARGET, where SOURCE is the symlink that will be created and TARGET is the symlink target.

     For instance, -S /opt/gnu/bin=bin creates a /opt/gnu/bin symlink pointing to the bin sub-directory of the profile.

--save-provenance
     Save provenance information for the packages passed on the command line. Provenance information includes the URL and commit of the channels in use (see Channels).

     Provenance information is saved in the /gnu/store/...-profile/manifest file in the pack, along with the usual package metadata---the name and version of each package, their propagated inputs, and so on.  It is useful information to the recipient of the pack, who then knows how the pack was (supposedly) obtained.

     This option is not enabled by default because, like timestamps, provenance information contributes nothing to the build process.  In other words, there is an infinity of channel URLs and commit IDs that can lead to the same pack. Recording such ``silent'' metadata in the output thus potentially breaks the source-to-binary bitwise reproducibility property.

--root=FILE
-r FILE
     Make FILE a symlink to the resulting pack, and register it as a garbage collector root.

--localstatedir
--profile-name=NAME
     Include the ``local state directory'', /var/guix, in the resulting pack, and notably the /var/guix/profiles/per-user/root/NAME profile---by default NAME is guix-profile, which corresponds to ~root/.guix-profile.

     /var/guix contains the store database (see The Store) as well as garbage-collector roots (see Invoking guix gc).  Providing it in the pack means that the store is ``complete'' and manageable by Guix; not providing it pack means that the store is ``dead'': items cannot be added to it or removed from it after extraction of the pack.

     One use case for this is the Guix self-contained binary tarball (see Binary Installation).

--derivation
-d
     Print the name of the derivation that builds the pack.

--bootstrap
     Use the bootstrap binaries to build the pack.  This option is only useful to Guix developers.

In addition, guix pack supports all the common build options (see Common Build Options) and all the package transformation options (see Package Transformation Options).

The GCC toolchain
=================

If you need a complete toolchain for compiling and linking C or C++ source code, use the gcc-toolchain package.  This package provides a complete GCC toolchain for C/C++ development, including GCC itself, the GNU C Library (headers and binaries, plus debugging symbols in the debug output), Binutils, and a linker wrapper.

The wrapper's purpose is to inspect the -L and -l switches passed to the linker, add corresponding -rpath arguments, and invoke the actual linker with this new set of arguments.  You can instruct the wrapper to refuse to link against libraries not in the store by setting the GUIX_LD_WRAPPER_ALLOW_IMPURITIES environment variable to no.

The package gfortran-toolchain provides a complete GCC toolchain for Fortran development.  For other languages, please use guix search gcc toolchain (see Invoking guix package).

Invoking guix git authenticate
==============================

The guix git authenticate command authenticates a Git checkout following the same rule as for channels (see channel authentication).  That is, starting from a given commit, it ensures that all subsequent commits are signed by an OpenPGP key whose fingerprint appears in the .guix-authorizations file of its parent commit(s).

You will find this command useful if you maintain a channel.  But in fact, this authentication mechanism is useful in a broader context, so you might want to use it for Git repositories that have nothing to do with Guix.

The general syntax is:

     guix git authenticate COMMIT SIGNER [OPTIONS...]

By default, this command authenticates the Git checkout in the current directory; it outputs nothing and exits with exit code zero on success and non-zero on failure.  COMMIT above denotes the first commit where authentication takes place, and SIGNER is the OpenPGP fingerprint of public key used to sign COMMIT.  Together, they form a ``channel introduction'' (see channel introduction).  The options below allow you to fine-tune the process.

--repository=DIRECTORY
-r DIRECTORY
     Open the Git repository in DIRECTORY instead of the current directory.

--keyring=REFERENCE
-k REFERENCE
     Load OpenPGP keyring from REFERENCE, the reference of a branch such as origin/keyring or my-keyring.  The branch must contain OpenPGP public keys in .key files, either in binary form or ``ASCII-armored''.  By default the keyring is loaded from the branch named keyring.

--stats
     Display commit signing statistics upon completion.

--cache-key=KEY
     Previously-authenticated commits are cached in a file under ~/.cache/guix/authentication.  This option forces the cache to be stored in file KEY in that directory.

--historical-authorizations=FILE
     By default, any commit whose parent commit(s) lack the .guix-authorizations file is considered inauthentic.  In contrast, this option considers the authorizations in FILE for any commit that lacks .guix-authorizations.  The format of FILE is the same as that of .guix-authorizations (see .guix-authorizations format).

Programming Interface
*********************

GNU Guix provides several Scheme programming interfaces (APIs) to define, build, and query packages.  The first interface allows users to write high-level package definitions.  These definitions refer to familiar packaging concepts, such as the name and version of a package, its build system, and its dependencies.  These definitions can then be turned into concrete build actions.

Build actions are performed by the Guix daemon, on behalf of users.  In a standard setup, the daemon has write access to the store---the /gnu/store directory---whereas users do not.  The recommended setup also has the daemon perform builds in chroots, under specific build users, to minimize interference with the rest of the system.

Lower-level APIs are available to interact with the daemon and the store.  To instruct the daemon to perform a build action, users actually provide it with a derivation.  A derivation is a low-level representation of the build actions to be taken, and the environment in which they should occur---derivations are to package definitions what assembly is to C programs.  The term ``derivation'' comes from the fact that build results derive from them.

This chapter describes all these APIs in turn, starting from high-level package definitions.

Package Modules
===============

From a programming viewpoint, the package definitions of the GNU distribution are provided by Guile modules in the (gnu packages ...) name space (Note that packages under the (gnu packages ...) module name space are not necessarily ``GNU packages''.  This module naming scheme follows the usual Guile module naming convention: gnu means that these modules are distributed as part of the GNU system, and packages identifies modules that define packages.)  (see Guile modules (GNU Guile Reference Manual)).  For instance, the (gnu packages emacs) module exports a variable named emacs, which is bound to a <package> object (see Defining Packages).

The (gnu packages ...) module name space is automatically scanned for packages by the command-line tools.  For instance, when running guix install emacs, all the (gnu packages ...) modules are scanned until one that exports a package object whose name is emacs is found.  This package search facility is implemented in the (gnu packages) module.

Users can store package definitions in modules with different names---e.g., (my-packages emacs) (Note that the file name and module name must match.  For instance, the (my-packages emacs) module must be stored in a my-packages/emacs.scm file relative to the load path specified with --load-path or GUIX_PACKAGE_PATH.  See Modules and the File System (GNU Guile Reference Manual), for details.).  There are two ways to make these package definitions visible to the user interfaces:

 1. By adding the directory containing your package modules to the search path with the -L flag of guix package and other commands (see Common Build Options), or by setting the GUIX_PACKAGE_PATH environment variable described below.

 2. By defining a channel and configuring guix pull so that it pulls from it.  A channel is essentially a Git repository containing package modules.  See Channels, for more information on how to define and use channels.

GUIX_PACKAGE_PATH works similarly to other search path variables:

 -- Environment Variable: GUIX_PACKAGE_PATH
     This is a colon-separated list of directories to search for additional package modules.  Directories listed in this variable take precedence over the own modules of the distribution.

The distribution is fully bootstrapped and self-contained: each package is built based solely on other packages in the distribution.  The root of this dependency graph is a small set of bootstrap binaries, provided by the (gnu packages bootstrap) module.  For more information on bootstrapping, see Bootstrapping.

Defining Packages
=================

The high-level interface to package definitions is implemented in the (guix packages) and (guix build-system) modules.  As an example, the package definition, or recipe, for the GNU Hello package looks like this:

     (define-module (gnu packages hello)
       #:use-module (guix packages)
       #:use-module (guix download)
       #:use-module (guix build-system gnu)
       #:use-module (guix licenses)
       #:use-module (gnu packages gawk))

     (define-public hello
       (package
         (name "hello")
         (version "2.10")
         (source (origin
                   (method url-fetch)
                   (uri (string-append "mirror://gnu/hello/hello-" version
                                       ".tar.gz"))
                   (sha256
                    (base32
                     "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
         (build-system gnu-build-system)
         (arguments '(#:configure-flags '("--enable-silent-rules")))
         (inputs (list gawk))
         (synopsis "Hello, GNU world: An example GNU package")
         (description "Guess what GNU Hello prints!")
         (home-page "https://www.gnu.org/software/hello/")
         (license gpl3+)))

Without being a Scheme expert, the reader may have guessed the meaning of the various fields here.  This expression binds the variable hello to a <package> object, which is essentially a record (see Scheme records (GNU Guile Reference Manual)). This package object can be inspected using procedures found in the (guix packages) module; for instance, (package-name hello) returns---surprise!---"hello".

With luck, you may be able to import part or all of the definition of the package you are interested in from another repository, using the guix import command (see Invoking guix import).

In the example above, hello is defined in a module of its own, (gnu packages hello).  Technically, this is not strictly necessary, but it is convenient to do so: all the packages defined in modules under (gnu packages ...) are automatically known to the command-line tools (see Package Modules).

There are a few points worth noting in the above package definition:

  * The source field of the package is an <origin> object (see origin Reference, for the complete reference). Here, the url-fetch method from (guix download) is used, meaning that the source is a file to be downloaded over FTP or HTTP.

     The mirror://gnu prefix instructs url-fetch to use one of the GNU mirrors defined in (guix download).

     The sha256 field specifies the expected SHA256 hash of the file being downloaded.  It is mandatory, and allows Guix to check the integrity of the file.  The (base32 ...) form introduces the base32 representation of the hash.  You can obtain this information with guix download (see Invoking guix download) and guix hash (see Invoking guix hash).

     When needed, the origin form can also have a patches field listing patches to be applied, and a snippet field giving a Scheme expression to modify the source code.

  * The build-system field specifies the procedure to build the package (see Build Systems).  Here, gnu-build-system represents the familiar GNU Build System, where packages may be configured, built, and installed with the usual ./configure && make && make check && make install command sequence.

     When you start packaging non-trivial software, you may need tools to manipulate those build phases, manipulate files, and so on.  See Build Utilities, for more on this.

  * The arguments field specifies options for the build system (see Build Systems).  Here it is interpreted by gnu-build-system as a request run configure with the --enable-silent-rules flag.

     What about these quote (') characters?  They are Scheme syntax to introduce a literal list; ' is synonymous with quote. Sometimes you'll also see ` (a backquote, synonymous with quasiquote) and , (a comma, synonymous with unquote). See quoting (GNU Guile Reference Manual), for details.  Here the value of the arguments field is a list of arguments passed to the build system down the road, as with apply (see apply (GNU Guile Reference Manual)).

     The hash-colon (#:) sequence defines a Scheme keyword (see Keywords (GNU Guile Reference Manual)), and #:configure-flags is a keyword used to pass a keyword argument to the build system (see Coding With Keywords (GNU Guile Reference Manual)).

  * The inputs field specifies inputs to the build process---i.e., build-time or run-time dependencies of the package.  Here, we add an input, a reference to the gawk variable; gawk is itself bound to a <package> object.

     Note that GCC, Coreutils, Bash, and other essential tools do not need to be specified as inputs here.  Instead, gnu-build-system takes care of ensuring that they are present (see Build Systems).

     However, any other dependencies need to be specified in the inputs field.  Any dependency not specified here will simply be unavailable to the build process, possibly leading to a build failure.

See package Reference, for a full description of possible fields.

     Intimidated by the Scheme language or curious about it?  The Cookbook has a short section to get started that recaps some of the things shown above and explains the fundamentals.  See A Scheme Crash Course (GNU Guix Cookbook), for more information.

Once a package definition is in place, the package may actually be built using the guix build command-line tool (see Invoking guix build), troubleshooting any build failures you encounter (see Debugging Build Failures).  You can easily jump back to the package definition using the guix edit command (see Invoking guix edit). See Packaging Guidelines, for more information on how to test package definitions, and Invoking guix lint, for information on how to check a definition for style conformance. Lastly, see Channels, for information on how to extend the distribution by adding your own package definitions in a ``channel''.

Finally, updating the package definition to a new upstream version can be partly automated by the guix refresh command (see Invoking guix refresh).

Behind the scenes, a derivation corresponding to the <package> object is first computed by the package-derivation procedure. That derivation is stored in a .drv file under /gnu/store. The build actions it prescribes may then be realized by using the build-derivations procedure (see The Store).

 -- Procedure: package-derivation store package [system]
     Return the <derivation> object of PACKAGE for SYSTEM (see Derivations).

     PACKAGE must be a valid <package> object, and SYSTEM must be a string denoting the target system type---e.g., "x86_64-linux" for an x86_64 Linux-based GNU system.  STORE must be a connection to the daemon, which operates on the store (see The Store).

Similarly, it is possible to compute a derivation that cross-builds a package for some other system:

 -- Procedure: package-cross-derivation store package target [system]
     Return the <derivation> object of PACKAGE cross-built from SYSTEM to TARGET.

     TARGET must be a valid GNU triplet denoting the target hardware and operating system, such as "aarch64-linux-gnu" (see Specifying Target Triplets (Autoconf)).

Once you have package definitions, you can easily define variants of those packages.  See Defining Package Variants, for more on that.

package Reference
-----------------

This section summarizes all the options available in package declarations (see Defining Packages).

 -- Data Type: package
     This is the data type representing a package recipe.

     name
          The name of the package, as a string.

     version
          The version of the package, as a string.  See Version Numbers, for guidelines.

     source
          An object telling how the source code for the package should be acquired.  Most of the time, this is an origin object, which denotes a file fetched from the Internet (see origin Reference).  It can also be any other ``file-like'' object such as a local-file, which denotes a file from the local file system (see local-file).

     build-system
          The build system that should be used to build the package (see Build Systems).

     arguments (default: '())
          The arguments that should be passed to the build system (see Build Systems).  This is a list, typically containing sequential keyword-value pairs, as in this example:

               (package
                 (name "example")
                 ;; several fields omitted
                 (arguments
                   (list #:tests? #f                     ;skip tests
                         #:make-flags #~'("VERBOSE=1")   ;pass flags to 'make'
                         #:configure-flags #~'("--enable-frobbing"))))

          The exact set of supported keywords depends on the build system (see Build Systems), but you will find that almost all of them honor #:configure-flags, #:make-flags, #:tests?, and #:phases.  The #:phases keyword in particular lets you modify the set of build phases for your package (see Build Phases).

          The REPL has dedicated commands to interactively inspect values of some of these arguments, as a convenient debugging aid (see Using Guix Interactively).

               Until version 1.3.0, the arguments field would typically use quote (') or quasiquote (`) and no G-expressions, like so:

                    (package
                      ;; several fields omitted
                      (arguments   ;old-style quoted arguments
                       '(#:tests? #f
                         #:configure-flags '("--enable-frobbing"))))

               To convert from that style to the one shown above, you can run guix style -S arguments PACKAGE (see Invoking guix style).

     inputs (default: '())
     native-inputs (default: '())
     propagated-inputs (default: '())
          These fields list dependencies of the package.  Each element of these lists is either a package, origin, or other ``file-like object'' (see G-Expressions); to specify the output of that file-like object that should be used, pass a two-element list where the second element is the output (see Packages with Multiple Outputs, for more on package outputs).  For example, the list below specifies three inputs:

               (list libffi libunistring
                     `(,glib "bin"))      ;the "bin" output of GLib

          In the example above, the "out" output of libffi and libunistring is used.

               Until version 1.3.0, input lists were a list of tuples, where each tuple has a label for the input (a string) as its first element, a package, origin, or derivation as its second element, and optionally the name of the output thereof that should be used, which defaults to "out".  For example, the list below is equivalent to the one above, but using the old input style:

                    ;; Old input style (deprecated).
                    `(("libffi" ,libffi)
                      ("libunistring" ,libunistring)
                      ("glib:bin" ,glib "bin"))  ;the "bin" output of GLib

               This style is now deprecated; it is still supported but support will be removed in a future version.  It should not be used for new package definitions.  See Invoking guix style, on how to migrate to the new style.

          The distinction between native-inputs and inputs is necessary when considering cross-compilation.  When cross-compiling, dependencies listed in inputs are built for the target architecture; conversely, dependencies listed in native-inputs are built for the architecture of the build machine.

          native-inputs is typically used to list tools needed at build time, but not at run time, such as Autoconf, Automake, pkg-config, Gettext, or Bison.  guix lint can report likely mistakes in this area (see Invoking guix lint).

          Lastly, propagated-inputs is similar to inputs, but the specified packages will be automatically installed to profiles (see the role of profiles in Guix) alongside the package they belong to (see guix package, for information on how guix package deals with propagated inputs).

          For example this is necessary when packaging a C/C++ library that needs headers of another library to compile, or when a pkg-config file refers to another one via its Requires field.

          Another example where propagated-inputs is useful is for languages that lack a facility to record the run-time search path akin to the RUNPATH of ELF files; this includes Guile, Python, Perl, and more.  When packaging libraries written in those languages, ensure they can find library code they depend on at run time by listing run-time dependencies in propagated-inputs rather than inputs.

     outputs (default: '("out"))
          The list of output names of the package.  See Packages with Multiple Outputs, for typical uses of additional outputs.

     native-search-paths (default: '())
     search-paths (default: '())
          A list of search-path-specification objects describing search-path environment variables honored by the package.  See Search Paths, for more on search path specifications.

          As for inputs, the distinction between native-search-paths and search-paths only matters when cross-compiling.  In a cross-compilation context, native-search-paths applies exclusively to native inputs whereas search-paths applies only to host inputs.

          Packages such as cross-compilers care about target inputs---for instance, our (modified) GCC cross-compiler has CROSS_C_INCLUDE_PATH in search-paths, which allows it to pick .h files for the target system and not those of native inputs.  For the majority of packages though, only native-search-paths makes sense.

     replacement (default: #f)
          This must be either #f or a package object that will be used as a replacement for this package.  See grafts, for details.

     synopsis
          A one-line description of the package.

     description
          A more elaborate description of the package, as a string in Texinfo syntax.

     license
          The license of the package; a value from (guix licenses), or a list of such values.

     home-page
          The URL to the home-page of the package, as a string.

     supported-systems (default: %supported-systems)
          The list of systems supported by the package, as strings of the form architecture-kernel, for example "x86_64-linux".

     location (default: source location of the package form)
          The source location of the package.  It is useful to override this when inheriting from another package, in which case this field is not automatically corrected.

 -- Macro: this-package
     When used in the lexical scope of a package field definition, this identifier resolves to the package being defined.

     The example below shows how to add a package as a native input of itself when cross-compiling:

          (package
            (name "guile")
            ;; ...

            ;; When cross-compiled, Guile, for example, depends on
            ;; a native version of itself.  Add it here.
            (native-inputs (if (%current-target-system)
                               (list this-package)
                               '())))

     It is an error to refer to this-package outside a package definition.

The following helper procedures are provided to help deal with package inputs.

 -- Procedure: lookup-package-input package name
 -- Procedure: lookup-package-native-input package name
 -- Procedure: lookup-package-propagated-input package name
 -- Procedure: lookup-package-direct-input package name
     Look up NAME among PACKAGE's inputs (or native, propagated, or direct inputs).  Return it if found, #f otherwise.

     NAME is the name of a package depended on.  Here's how you might use it:

          (use-modules (guix packages) (gnu packages base))

          (lookup-package-direct-input coreutils "gmp")
          => #<package gmp@6.2.1 ...>

     In this example we obtain the gmp package that is among the direct inputs of coreutils.

Sometimes you will want to obtain the list of inputs needed to develop a package---all the inputs that are visible when the package is compiled.  This is what the package-development-inputs procedure returns.

 -- Procedure: package-development-inputs package [system] [#:target #f]
     Return the list of inputs required by PACKAGE for development purposes on SYSTEM.  When TARGET is true, return the inputs needed to cross-compile PACKAGE from SYSTEM to TARGET, where TARGET is a triplet such as "aarch64-linux-gnu".

     Note that the result includes both explicit inputs and implicit inputs---inputs automatically added by the build system (see Build Systems).  Let us take the hello package to illustrate that:

          (use-modules (gnu packages base) (guix packages))

          hello
          => #<package hello@2.10 gnu/packages/base.scm:79 7f585d4f6790>

          (package-direct-inputs hello)
          => ()

          (package-development-inputs hello)
          => (("source" ...) ("tar" #<package tar@1.32 ...>) ...)

     In this example, package-direct-inputs returns the empty list, because hello has zero explicit dependencies.  Conversely, package-development-inputs includes inputs implicitly added by gnu-build-system that are required to build hello: tar, gzip, GCC, libc, Bash, and more.  To visualize it, guix graph hello would show you explicit inputs, whereas guix graph -t bag hello would include implicit inputs (see Invoking guix graph).

Because packages are regular Scheme objects that capture a complete dependency graph and associated build procedures, it is often useful to write procedures that take a package and return a modified version thereof according to some parameters.  Below are a few examples.

 -- Procedure: package-with-c-toolchain package toolchain
     Return a variant of PACKAGE that uses TOOLCHAIN instead of the default GNU C/C++ toolchain.  TOOLCHAIN must be a list of inputs (label/package tuples) providing equivalent functionality, such as the gcc-toolchain package.

     The example below returns a variant of the hello package built with GCC 10.x and the rest of the GNU tool chain (Binutils and the GNU C Library) instead of the default tool chain:

          (let ((toolchain (specification->package "gcc-toolchain@10")))
            (package-with-c-toolchain hello `(("toolchain" ,toolchain))))

     The build tool chain is part of the implicit inputs of packages---it's usually not listed as part of the various ``inputs'' fields and is instead pulled in by the build system.  Consequently, this procedure works by changing the build system of PACKAGE so that it pulls in TOOLCHAIN instead of the defaults.  Build Systems, for more on build systems.

origin Reference
----------------

This section documents origins.  An origin declaration specifies data that must be ``produced''---downloaded, usually---and whose content hash is known in advance.  Origins are primarily used to represent the source code of packages (see Defining Packages).  For that reason, the origin form allows you to declare patches to apply to the original source code as well as code snippets to modify it.

 -- Data Type: origin
     This is the data type representing a source code origin.

     uri
          An object containing the URI of the source.  The object type depends on the method (see below).  For example, when using the URL-FETCH method of (guix download), the valid uri values are: a URL represented as a string, or a list thereof.

     method
          A monadic procedure that handles the given URI.  The procedure must accept at least three arguments: the value of the uri field and the hash algorithm and hash value specified by the hash field. It must return a store item or a derivation in the store monad (see The Store Monad); most methods return a fixed-output derivation (see Derivations).

          Commonly used methods include url-fetch, which fetches data from a URL, and git-fetch, which fetches data from a Git repository (see below).

     sha256
          A bytevector containing the SHA-256 hash of the source.  This is equivalent to providing a content-hash SHA256 object in the hash field described below.

     hash
          The content-hash object of the source---see below for how to use content-hash.

          You can obtain this information using guix download (see Invoking guix download) or guix hash (see Invoking guix hash).

     file-name (default: #f)
          The file name under which the source code should be saved.  When this is #f, a sensible default value will be used in most cases.  In case the source is fetched from a URL, the file name from the URL will be used.  For version control checkouts, it is recommended to provide the file name explicitly because the default is not very descriptive.

     patches (default: '())
          A list of file names, origins, or file-like objects (see file-like objects) pointing to patches to be applied to the source.

          This list of patches must be unconditional.  In particular, it cannot depend on the value of %current-system or %current-target-system.

     snippet (default: #f)
          A G-expression (see G-Expressions) or S-expression that will be run in the source directory.  This is a convenient way to modify the source, sometimes more convenient than a patch.

     patch-flags (default: '("-p1"))
          A list of command-line flags that should be passed to the patch command.

     patch-inputs (default: #f)
          Input packages or derivations to the patching process.  When this is #f, the usual set of inputs necessary for patching are provided, such as GNU Patch.

     modules (default: '())
          A list of Guile modules that should be loaded during the patching process and while running the code in the snippet field.

     patch-guile (default: #f)
          The Guile package that should be used in the patching process.  When this is #f, a sensible default is used.

 -- Data Type: content-hash VALUE [ALGORITHM]
     Construct a content hash object for the given ALGORITHM, and with VALUE as its hash value.  When ALGORITHM is omitted, assume it is sha256.

     VALUE can be a literal string, in which case it is base32-decoded, or it can be a bytevector.

     The following forms are all equivalent:

          (content-hash "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj")
          (content-hash "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj"
                        sha256)
          (content-hash (base32
                         "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj"))
          (content-hash (base64 "kkb+RPaP7uyMZmu4eXPVkM4BN8yhRd8BTHLslb6f/Rc=")
                        sha256)

     Technically, content-hash is currently implemented as a macro. It performs sanity checks at macro-expansion time, when possible, such as ensuring that VALUE has the right size for ALGORITHM.

As we have seen above, how exactly the data an origin refers to is retrieved is determined by its method field.  The (guix download) module provides the most common method, url-fetch, described below.

 -- Procedure: url-fetch url hash-algo hash [name] [#:executable? #f]
     Return a fixed-output derivation that fetches data from URL (a string, or a list of strings denoting alternate URLs), which is expected to have hash HASH of type HASH-ALGO (a symbol).  By default, the file name is the base name of URL; optionally, NAME can specify a different file name.  When EXECUTABLE? is true, make the downloaded file executable.

     When one of the URL starts with mirror://, then its host part is interpreted as the name of a mirror scheme, taken from %mirror-file.

     Alternatively, when URL starts with file://, return the corresponding file name in the store.

Likewise, the (guix git-download) module defines the git-fetch origin method, which fetches data from a Git version control repository, and the git-reference data type to describe the repository and revision to fetch.

 -- Procedure: git-fetch ref hash-algo hash
     Return a fixed-output derivation that fetches REF, a <git-reference> object.  The output is expected to have recursive hash HASH of type HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f.

 -- Procedure: git-fetch/lfs ref hash-algo hash
     This is a variant of the git-fetch procedure that supports the Git LFS (Large File Storage) extension.  This may be useful to pull some binary test data to run the test suite of a package, for example.

 -- Data Type: git-reference
     This data type represents a Git reference for git-fetch to retrieve.

     url
          The URL of the Git repository to clone.

     commit
          This string denotes either the commit to fetch (a hexadecimal string), or the tag to fetch.  You can also use a ``short'' commit ID or a git describe style identifier such as v1.0.1-10-g58d7909c97.

     recursive? (default: #f)
          This Boolean indicates whether to recursively fetch Git sub-modules.

     The example below denotes the v2.10 tag of the GNU Hello repository:

          (git-reference
            (url "https://git.savannah.gnu.org/git/hello.git")
            (commit "v2.10"))

     This is equivalent to the reference below, which explicitly names the commit:

          (git-reference
            (url "https://git.savannah.gnu.org/git/hello.git")
            (commit "dc7dc56a00e48fe6f231a58f6537139fe2908fb9"))

For Mercurial repositories, the module (guix hg-download) defines the hg-fetch origin method and hg-reference data type for support of the Mercurial version control system.

 -- Procedure: hg-fetch ref hash-algo hash [name]
     Return a fixed-output derivation that fetches REF, a <hg-reference> object.  The output is expected to have recursive hash HASH of type HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f.

 -- Data Type: hg-reference
     This data type represents a Mercurial reference for hg-fetch to retrieve.

     url
          The URL of the Mercurial repository to clone.

     revision
          This string denotes revision to fetch specified as a number.

For Subversion repositories, the module (guix svn-download) defines the svn-fetch origin method and svn-reference data type for support of the Subversion version control system.

 -- Procedure: svn-fetch ref hash-algo hash [name]
     Return a fixed-output derivation that fetches REF, a <svn-reference> object.  The output is expected to have recursive hash HASH of type HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f.

 -- Data Type: svn-reference
     This data type represents a Subversion reference for svn-fetch to retrieve.

     url
          The URL of the Subversion repository to clone.

     revision
          This string denotes revision to fetch specified as a number.

     recursive? (default: #f)
          This Boolean indicates whether to recursively fetch Subversion ``externals''.

     user-name (default: #f)
          The name of an account that has read-access to the repository, if the repository isn't public.

     password (default: #f)
          Password to access the Subversion repository, if required.

For Bazaar repositories, the module (guix bzr-download) defines the bzr-fetch origin method and bzr-reference data type for support of the Bazaar version control system.

 -- Procedure: bzr-fetch ref hash-algo hash [name]
     Return a fixed-output derivation that fetches REF, a <bzr-reference> object.  The output is expected to have recursive hash HASH of type HASH-ALGO (a symbol).  Use NAME as the file name, or a generic name if #f.

 -- Data Type: bzr-reference
     This data type represents a Bazaar reference for bzr-fetch to retrieve.

     url
          The URL of the Bazaar repository to clone.

     revision
          This string denotes revision to fetch specified as a number.

Defining Package Variants
=========================

One of the nice things with Guix is that, given a package definition, you can easily derive variants of that package---for a different upstream version, with different dependencies, different compilation options, and so on.  Some of these custom packages can be defined straight from the command line (see Package Transformation Options). This section describes how to define package variants in code.  This can be useful in ``manifests'' (see Writing Manifests) and in your own package collection (see Creating a Channel), among others!

As discussed earlier, packages are first-class objects in the Scheme language.  The (guix packages) module provides the package construct to define new package objects (see package Reference). The easiest way to define a package variant is using the inherit keyword together with package.  This allows you to inherit from a package definition while overriding the fields you want.

For example, given the hello variable, which contains a definition for the current version of GNU Hello, here's how you would define a variant for version 2.2 (released in 2006, it's vintage!):

     (use-modules (gnu packages base))    ;for 'hello'

     (define hello-2.2
       (package
         (inherit hello)
         (version "2.2")
         (source (origin
                   (method url-fetch)
                   (uri (string-append "mirror://gnu/hello/hello-" version
                                       ".tar.gz"))
                   (sha256
                    (base32
                     "0lappv4slgb5spyqbh6yl5r013zv72yqg2pcl30mginf3wdqd8k9"))))))

The example above corresponds to what the --with-version or --with-source package transformations option do. Essentially hello-2.2 preserves all the fields of hello, except version and source, which it overrides.  Note that the original hello variable is still there, in the (gnu packages base) module, unchanged.  When you define a custom package like this, you are really adding a new package definition; the original one remains available.

You can just as well define variants with a different set of dependencies than the original package.  For example, the default gdb package depends on guile, but since that is an optional dependency, you can define a variant that removes that dependency like so:

     (use-modules (gnu packages gdb))   ;for 'gdb'

     (define gdb-sans-guile
       (package
         (inherit gdb)
         (inputs (modify-inputs (package-inputs gdb)
                   (delete "guile")))))

The modify-inputs form above removes the "guile" package from the inputs field of gdb.  The modify-inputs macro is a helper that can prove useful anytime you want to remove, add, or replace package inputs.

 -- Macro: modify-inputs inputs clauses
     Modify the given package inputs, as returned by package-inputs & co., according to the given clauses.  Each clause must have one of the following forms:

     (delete NAME...)
          Delete from the inputs packages with the given NAMEs (strings).

     (prepend PACKAGE...)
          Add PACKAGEs to the front of the input list.

     (append PACKAGE...)
          Add PACKAGEs to the end of the input list.

     (replace NAME REPLACEMENT)
          Replace the package called NAME with REPLACEMENT.

     The example below removes the GMP and ACL inputs of Coreutils and adds libcap to the front of the input list:

          (modify-inputs (package-inputs coreutils)
            (delete "gmp" "acl")
            (prepend libcap))

     The example below replaces the guile package from the inputs of guile-redis with guile-2.2:

          (modify-inputs (package-inputs guile-redis)
            (replace "guile" guile-2.2))

     The last type of clause is append, to add inputs at the back of the list.

In some cases, you may find it useful to write functions (``procedures'', in Scheme parlance) that return a package based on some parameters.  For example, consider the luasocket library for the Lua programming language.  We want to create luasocket packages for major versions of Lua.  One way to do that is to define a procedure that takes a Lua package and returns a luasocket package that depends on it:

     (define (make-lua-socket name lua)
       ;; Return a luasocket package built with LUA.
       (package
         (name name)
         (version "3.0")
         ;; several fields omitted
         (inputs (list lua))
         (synopsis "Socket library for Lua")))

     (define-public lua5.1-socket
       (make-lua-socket "lua5.1-socket" lua-5.1))

     (define-public lua5.2-socket
       (make-lua-socket "lua5.2-socket" lua-5.2))

Here we have defined packages lua5.1-socket and lua5.2-socket by calling make-lua-socket with different arguments.  See Procedures (GNU Guile Reference Manual), for more info on procedures.  Having top-level public definitions for these two packages means that they can be referred to from the command line (see Package Modules).

These are pretty simple package variants.  As a convenience, the (guix transformations) module provides a high-level interface that directly maps to the more sophisticated package transformation options (see Package Transformation Options):

 -- Procedure: options->transformation opts
     Return a procedure that, when passed an object to build (package, derivation, etc.), applies the transformations specified by OPTS and returns the resulting objects.  OPTS must be a list of symbol/string pairs such as:

          ((with-branch . "guile-gcrypt=master")
           (without-tests . "libgcrypt"))

     Each symbol names a transformation and the corresponding string is an argument to that transformation.

For instance, a manifest equivalent to this command:

     guix build guix \
       --with-branch=guile-gcrypt=master \
       --with-debug-info=zlib

... would look like this:

     (use-modules (guix transformations))

     (define transform
       ;; The package transformation procedure.
       (options->transformation
        '((with-branch . "guile-gcrypt=master")
          (with-debug-info . "zlib"))))

     (packages->manifest
      (list (transform (specification->package "guix"))))

The options->transformation procedure is convenient, but it's perhaps also not as flexible as you may like.  How is it implemented? The astute reader probably noticed that most package transformation options go beyond the superficial changes shown in the first examples of this section: they involve input rewriting, whereby the dependency graph of a package is rewritten by replacing specific inputs by others.

Dependency graph rewriting, for the purposes of swapping packages in the graph, is what the package-input-rewriting procedure in (guix packages) implements.

 -- Procedure: package-input-rewriting replacements [rewrite-name] [#:deep? #t]
     Return a procedure that, when passed a package, replaces its direct and indirect dependencies, including implicit inputs when DEEP? is true, according to REPLACEMENTS.  REPLACEMENTS is a list of package pairs; the first element of each pair is the package to replace, and the second one is the replacement.

     Optionally, REWRITE-NAME is a one-argument procedure that takes the name of a package and returns its new name after rewrite.

Consider this example:

     (define libressl-instead-of-openssl
       ;; This is a procedure to replace OPENSSL by LIBRESSL,
       ;; recursively.
       (package-input-rewriting `((,openssl . ,libressl))))

     (define git-with-libressl
       (libressl-instead-of-openssl git))

Here we first define a rewriting procedure that replaces OPENSSL with LIBRESSL.  Then we use it to define a variant of the GIT package that uses LIBRESSL instead of OPENSSL. This is exactly what the --with-input command-line option does (see --with-input).

The following variant of package-input-rewriting can match packages to be replaced by name rather than by identity.

 -- Procedure: package-input-rewriting/spec REPLACEMENTS [#:deep? #t]
     Return a procedure that, given a package, applies the given REPLACEMENTS to all the package graph, including implicit inputs unless DEEP? is false.

     REPLACEMENTS is a list of spec/procedures pair; each spec is a package specification such as "gcc" or "guile@2", and each procedure takes a matching package and returns a replacement for that package.  Matching packages that have the hidden? property set are not replaced.

The example above could be rewritten this way:

     (define libressl-instead-of-openssl
       ;; Replace all the packages called "openssl" with LibreSSL.
       (package-input-rewriting/spec `(("openssl" . ,(const libressl)))))

The key difference here is that, this time, packages are matched by spec and not by identity.  In other words, any package in the graph that is called openssl will be replaced.

A more generic procedure to rewrite a package dependency graph is package-mapping: it supports arbitrary changes to nodes in the graph.

 -- Procedure: package-mapping proc [cut?] [#:deep? #f]
     Return a procedure that, given a package, applies PROC to all the packages depended on and returns the resulting package.  The procedure stops recursion when CUT? returns true for a given package.  When DEEP? is true, PROC is applied to implicit inputs as well.

     Understanding what a variant really looks like can be difficult as one starts combining the tools shown above.  There are several ways to inspect a package before attempting to build it that can prove handy:

       * You can inspect the package interactively at the REPL, for instance to view its inputs, the code of its build phases, or its configure flags (see Using Guix Interactively).

       * When rewriting dependencies, guix graph can often help visualize the changes that are made (see Invoking guix graph).

Writing Manifests
=================

guix commands let you specify package lists on the command line.  This is convenient, but as the command line becomes longer and less trivial, it quickly becomes more convenient to have that package list in what we call a manifest.  A manifest is some sort of a ``bill of materials'' that defines a package set.  You would typically come up with a code snippet that builds the manifest, store it in a file, say manifest.scm, and then pass that file to the -m (or --manifest) option that many guix commands support.  For example, here's what a manifest for a simple package set might look like:

     ;; Manifest for three packages.
     (specifications->manifest '("gcc-toolchain" "make" "git"))

Once you have that manifest, you can pass it, for example, to guix package to install just those three packages to your profile (see -m option of guix package):

     guix package -m manifest.scm

... or you can pass it to guix shell (see -m option of guix shell) to spawn an ephemeral environment:

     guix shell -m manifest.scm

... or you can pass it to guix pack in pretty much the same way (see -m option of guix pack). You can store the manifest under version control, share it with others so they can easily get set up, etc.

But how do you write your first manifest?  To get started, maybe you'll want to write a manifest that mirrors what you already have in a profile.  Rather than start from a blank page, guix package can generate a manifest for you (see guix package --export-manifest):

     # Write to 'manifest.scm' a manifest corresponding to the
     # default profile, ~/.guix-profile.
     guix package --export-manifest > manifest.scm

Or maybe you'll want to ``translate'' command-line arguments into a manifest.  In that case, guix shell can help (see guix shell --export-manifest):

     # Write a manifest for the packages specified on the command line.
     guix shell --export-manifest gcc-toolchain make git > manifest.scm

In both cases, the --export-manifest option tries hard to generate a faithful manifest; in particular, it takes package transformation options into account (see Package Transformation Options).

     Manifests are symbolic: they refer to packages of the channels currently in use (see Channels).  In the example above, gcc-toolchain might refer to version 11 today, but it might refer to version 13 two years from now.

     If you want to ``pin'' your software environment to specific package versions and variants, you need an additional piece of information: the list of channel revisions in use, as returned by guix describe.  See Replicating Guix, for more information.

Once you've obtained your first manifest, perhaps you'll want to customize it.  Since your manifest is code, you now have access to all the Guix programming interfaces!

Let's assume you want a manifest to deploy a custom variant of GDB, the GNU Debugger, that does not depend on Guile, together with another package.  Building on the example seen in the previous section (see Defining Package Variants), you can write a manifest along these lines:

     (use-modules (guix packages)
                  (gnu packages gdb)               ;for 'gdb'
                  (gnu packages version-control))  ;for 'git'

     ;; Define a variant of GDB without a dependency on Guile.
     (define gdb-sans-guile
       (package
         (inherit gdb)
         (inputs (modify-inputs (package-inputs gdb)
                   (delete "guile")))))

     ;; Return a manifest containing that one package plus Git.
     (packages->manifest (list gdb-sans-guile git))

Note that in this example, the manifest directly refers to the gdb and git variables, which are bound to a package object (see package Reference), instead of calling specifications->manifest to look up packages by name as we did before.  The use-modules form at the top lets us access the core package interface (see Defining Packages) and the modules that define gdb and git (see Package Modules).  Seamlessly, we're weaving all this together---the possibilities are endless, unleash your creativity!

The data type for manifests as well as supporting procedures are defined in the (guix profiles) module, which is automatically available to code passed to -m.  The reference follows.

 -- Data Type: manifest
     Data type representing a manifest.

     It currently has one field:

     entries
          This must be a list of manifest-entry records---see below.

 -- Data Type: manifest-entry
     Data type representing a manifest entry.  A manifest entry contains essential metadata: a name and version string, the object (usually a package) for that entry, the desired output (see Packages with Multiple Outputs), and a number of optional pieces of information detailed below.

     Most of the time, you won't build a manifest entry directly; instead, you will pass a package to package->manifest-entry, described below.  In some unusual cases though, you might want to create manifest entries for things that are not packages, as in this example:

          ;; Manually build a single manifest entry for a non-package object.
          (let ((hello (program-file "hello" #~(display "Hi!"))))
            (manifest-entry
              (name "foo")
              (version "42")
              (item
               (computed-file "hello-directory"
                               #~(let ((bin (string-append #$output "/bin")))
                                   (mkdir #$output) (mkdir bin)
                                    (symlink #$hello
                                             (string-append bin "/hello")))))))

     The available fields are the following:

     name
     version
          Name and version string for this entry.

     item
          A package or other file-like object (see file-like objects).

     output (default: "out")
          Output of item to use, in case item has multiple outputs (see Packages with Multiple Outputs).

     dependencies (default: '())
          List of manifest entries this entry depends on.  When building a profile, dependencies are added to the profile.

          Typically, the propagated inputs of a package (see propagated-inputs) end up having a corresponding manifest entry in among the dependencies of the package's own manifest entry.

     search-paths (default: '())
          The list of search path specifications honored by this entry (see Search Paths).

     properties (default: '())
          List of symbol/value pairs.  When building a profile, those properties get serialized.

          This can be used to piggyback additional metadata---e.g., the transformations applied to a package (see Package Transformation Options).

     parent (default: (delay #f))
          A promise pointing to the ``parent'' manifest entry.

          This is used as a hint to provide context when reporting an error related to a manifest entry coming from a dependencies field.

 -- Procedure: concatenate-manifests lst
     Concatenate the manifests listed in LST and return the resulting manifest.

 -- Procedure: package->manifest-entry package [output] [#:properties]
     Return a manifest entry for the OUTPUT of package PACKAGE, where OUTPUT defaults to "out", and with the given PROPERTIES.  By default PROPERTIES is the empty list or, if one or more package transformations were applied to PACKAGE, it is an association list representing those transformations, suitable as an argument to options->transformation (see options->transformation).

     The code snippet below builds a manifest with an entry for the default output and the send-email output of the git package:

          (use-modules (gnu packages version-control))

          (manifest (list (package->manifest-entry git)
                          (package->manifest-entry git "send-email")))

 -- Procedure: packages->manifest packages
     Return a list of manifest entries, one for each item listed in PACKAGES.  Elements of PACKAGES can be either package objects or package/string tuples denoting a specific output of a package.

     Using this procedure, the manifest above may be rewritten more concisely:

          (use-modules (gnu packages version-control))

          (packages->manifest (list git `(,git "send-email")))

 -- Procedure: package->development-manifest package [system] [#:target]
     Return a manifest for the development inputs of PACKAGE for SYSTEM, optionally when cross-compiling to TARGET. Development inputs include both explicit and implicit inputs of PACKAGE.

     Like the -D option of guix shell (see guix shell -D), the resulting manifest describes the environment in which one can develop PACKAGE.  For example, suppose you're willing to set up a development environment for Inkscape, with the addition of Git for version control; you can describe that ``bill of materials'' with the following manifest:

          (use-modules (gnu packages inkscape)          ;for 'inkscape'
                       (gnu packages version-control))  ;for 'git'

          (concatenate-manifests
           (list (package->development-manifest inkscape)
                 (packages->manifest (list git))))

     In this example, the development manifest that package->development-manifest returns includes the compiler (GCC), the many supporting libraries (Boost, GLib, GTK, etc.), and a couple of additional development tools---these are the dependencies guix show inkscape lists.

Last, the (gnu packages) module provides higher-level facilities to build manifests.  In particular, it lets you look up packages by name---see below.

 -- Procedure: specifications->manifest specs
     Given SPECS, a list of specifications such as "emacs@25.2" or "guile:debug", return a manifest.  Specs have the format that command-line tools such as guix install and guix package understand (see Invoking guix package).

     As an example, it lets you rewrite the Git manifest that we saw earlier like this:

          (specifications->manifest '("git" "git:send-email"))

     Notice that we do not need to worry about use-modules, importing the right set of modules, and referring to the right variables. Instead, we directly refer to packages in the same way as on the command line, which can often be more convenient.

Build Systems
=============

Each package definition specifies a build system and arguments for that build system (see Defining Packages).  This build-system field represents the build procedure of the package, as well as implicit dependencies of that build procedure.

Build systems are <build-system> objects.  The interface to create and manipulate them is provided by the (guix build-system) module, and actual build systems are exported by specific modules.

Under the hood, build systems first compile package objects to bags.  A bag is like a package, but with less ornamentation---in other words, a bag is a lower-level representation of a package, which includes all the inputs of that package, including some that were implicitly added by the build system.  This intermediate representation is then compiled to a derivation (see Derivations). The package-with-c-toolchain is an example of a way to change the implicit inputs that a package's build system pulls in (see package-with-c-toolchain).

Build systems accept an optional list of arguments.  In package definitions, these are passed via the arguments field (see Defining Packages).  They are typically keyword arguments (see keyword arguments in Guile (GNU Guile Reference Manual)).  The value of these arguments is usually evaluated in the build stratum---i.e., by a Guile process launched by the daemon (see Derivations).

The main build system is gnu-build-system, which implements the standard build procedure for GNU and many other packages.  It is provided by the (guix build-system gnu) module.

 -- Variable: gnu-build-system
     gnu-build-system represents the GNU Build System, and variants thereof (see configuration and makefile conventions (GNU Coding Standards)).

     In a nutshell, packages using it are configured, built, and installed with the usual ./configure && make && make check && make install command sequence.  In practice, a few additional steps are often needed. All these steps are split up in separate phases. See Build Phases, for more info on build phases and ways to customize them.

     In addition, this build system ensures that the ``standard'' environment for GNU packages is available.  This includes tools such as GCC, libc, Coreutils, Bash, Make, Diffutils, grep, and sed (see the (guix build-system gnu) module for a complete list).  We call these the implicit inputs of a package, because package definitions do not have to mention them.

     This build system supports a number of keyword arguments, which can be passed via the arguments field of a package.  Here are some of the main parameters:

     #:phases
          This argument specifies build-side code that evaluates to an alist of build phases.  See Build Phases, for more information.

     #:configure-flags
          This is a list of flags (strings) passed to the configure script.  See Defining Packages, for an example.

     #:make-flags
          This list of strings contains flags passed as arguments to make invocations in the build, check, and install phases.

     #:out-of-source?
          This Boolean, #f by default, indicates whether to run builds in a build directory separate from the source tree.

          When it is true, the configure phase creates a separate build directory, changes to that directory, and runs the configure script from there.  This is useful for packages that require it, such as glibc.

     #:tests?
          This Boolean, #t by default, indicates whether the check phase should run the package's test suite.

     #:test-target
          This string, "check" by default, gives the name of the makefile target used by the check phase.

     #:parallel-build?
     #:parallel-tests?
          These Boolean values specify whether to build, respectively run the test suite, in parallel, with the -j flag of make.  When they are true, make is passed -jN, where N is the number specified as the --cores option of guix-daemon or that of the guix client command (see --cores).

     #:validate-runpath?
          This Boolean, #t by default, determines whether to ``validate'' the RUNPATH of ELF binaries (.so shared libraries as well as executables) previously installed by the install phase. See the validate-runpath phase, for details.

     #:substitutable?
          This Boolean, #t by default, tells whether the package outputs should be substitutable---i.e., whether users should be able to obtain substitutes for them instead of building locally (see Substitutes).

     #:allowed-references
     #:disallowed-references
          When true, these arguments must be a list of dependencies that must not appear among the references of the build results.  If, upon build completion, some of these references are retained, the build process fails.

          This is useful to ensure that a package does not erroneously keep a reference to some of it build-time inputs, in cases where doing so would, for example, unnecessarily increase its size (see Invoking guix size).

     Most other build systems support these keyword arguments.

Other <build-system> objects are defined to support other conventions and tools used by free software packages.  They inherit most of gnu-build-system, and differ mainly in the set of inputs implicitly added to the build process, and in the list of phases executed.  Some of these build systems are listed below.

 -- Variable: agda-build-system
     This variable is exported by (guix build-system agda).  It implements a build procedure for Agda libraries.

     It adds agda to the set of inputs.  A different Agda can be specified with the #:agda key.

     The #:plan key is a list of cons cells (REGEXP . PARAMETERS), where REGEXP is a regexp that should match the .agda files to build, and PARAMETERS is an optional list of parameters that will be passed to agda when type-checking it.

     When the library uses Haskell to generate a file containing all imports, the convenience #:gnu-and-haskell? can be set to #t to add ghc and the standard inputs of gnu-build-system to the input list.  You will still need to manually add a phase or tweak the 'build phase, as in the definition of agda-stdlib.

 -- Variable: ant-build-system
     This variable is exported by (guix build-system ant).  It implements the build procedure for Java packages that can be built with Ant build tool (https://ant.apache.org/).

     It adds both ant and the Java Development Kit (JDK) as provided by the icedtea package to the set of inputs.  Different packages can be specified with the #:ant and #:jdk parameters, respectively.

     When the original package does not provide a suitable Ant build file, the parameter #:jar-name can be used to generate a minimal Ant build file build.xml with tasks to build the specified jar archive.  In this case the parameter #:source-dir can be used to specify the source sub-directory, defaulting to ``src''.

     The #:main-class parameter can be used with the minimal ant buildfile to specify the main class of the resulting jar.  This makes the jar file executable.  The #:test-include parameter can be used to specify the list of junit tests to run.  It defaults to (list "**/*Test.java").  The #:test-exclude can be used to disable some tests.  It defaults to (list "**/Abstract*.java"), because abstract classes cannot be run as tests.

     The parameter #:build-target can be used to specify the Ant task that should be run during the build phase.  By default the ``jar'' task will be run.

 -- Variable: android-ndk-build-system
     This variable is exported by (guix build-system android-ndk).  It implements a build procedure for Android NDK (native development kit) packages using a Guix-specific build process.

     The build system assumes that packages install their public interface (header) files to the subdirectory include of the out output and their libraries to the subdirectory lib the out output.

     It's also assumed that the union of all the dependencies of a package has no conflicting files.

     For the time being, cross-compilation is not supported - so right now the libraries and header files are assumed to be host tools.

 -- Variable: asdf-build-system/source
 -- Variable: asdf-build-system/sbcl
 -- Variable: asdf-build-system/ecl

     These variables, exported by (guix build-system asdf), implement build procedures for Common Lisp packages using ``ASDF'' (https://common-lisp.net/project/asdf/).  ASDF is a system definition facility for Common Lisp programs and libraries.

     The asdf-build-system/source system installs the packages in source form, and can be loaded using any common lisp implementation, via ASDF.  The others, such as asdf-build-system/sbcl, install binary systems in the format which a particular implementation understands. These build systems can also be used to produce executable programs, or lisp images which contain a set of packages pre-loaded.

     The build system uses naming conventions.  For binary packages, the package name should be prefixed with the lisp implementation, such as sbcl- for asdf-build-system/sbcl.

     Additionally, the corresponding source package should be labeled using the same convention as python packages (see Python Modules), using the cl- prefix.

     In order to create executable programs and images, the build-side procedures build-program and build-image can be used. They should be called in a build phase after the create-asdf-configuration phase, so that the system which was just built can be used within the resulting image.  build-program requires a list of Common Lisp expressions to be passed as the #:entry-program argument.

     By default, all the .asd files present in the sources are read to find system definitions.  The #:asd-files parameter can be used to specify the list of .asd files to read.  Furthermore, if the package defines a system for its tests in a separate file, it will be loaded before the tests are run if it is specified by the #:test-asd-file parameter.  If it is not set, the files <system>-tests.asd, <system>-test.asd, tests.asd, and test.asd will be tried if they exist.

     If for some reason the package must be named in a different way than the naming conventions suggest, or if several systems must be compiled, the #:asd-systems parameter can be used to specify the list of system names.

 -- Variable: cargo-build-system
     This variable is exported by (guix build-system cargo).  It supports builds of packages using Cargo, the build tool of the Rust programming language (https://www.rust-lang.org).

     It adds rustc and cargo to the set of inputs. A different Rust package can be specified with the #:rust parameter.

     Regular cargo dependencies should be added to the package definition similarly to other packages; those needed only at build time to native-inputs, others to inputs.  If you need to add source-only crates then you should add them to via the #:cargo-inputs parameter as a list of name and spec pairs, where the spec can be a package or a source definition.  Note that the spec must evaluate to a path to a gzipped tarball which includes a Cargo.toml file at its root, or it will be ignored.  Similarly, cargo dev-dependencies should be added to the package definition via the #:cargo-development-inputs parameter.

     In its configure phase, this build system will make any source inputs specified in the #:cargo-inputs and #:cargo-development-inputs parameters available to cargo.  It will also remove an included Cargo.lock file to be recreated by cargo during the build phase.  The package phase will run cargo package to create a source crate for future use.  The install phase installs the binaries defined by the crate.  Unless install-source? #f is defined it will also install a source crate repository of itself and unpacked sources, to ease in future hacking on rust packages.

 -- Variable: chicken-build-system
     This variable is exported by (guix build-system chicken).  It builds CHICKEN Scheme (https://call-cc.org/) modules, also called ``eggs'' or ``extensions''.  CHICKEN generates C source code, which then gets compiled by a C compiler, in this case GCC.

     This build system adds chicken to the package inputs, as well as the packages of gnu-build-system.

     The build system can't (yet) deduce the egg's name automatically, so just like with go-build-system and its #:import-path, you should define #:egg-name in the package's arguments field.

     For example, if you are packaging the srfi-1 egg:

          (arguments '(#:egg-name "srfi-1"))

     Egg dependencies must be defined in propagated-inputs, not inputs because CHICKEN doesn't embed absolute references in compiled eggs. Test dependencies should go to native-inputs, as usual.

 -- Variable: copy-build-system
     This variable is exported by (guix build-system copy).  It supports builds of simple packages that don't require much compiling, mostly just moving files around.

     It adds much of the gnu-build-system packages to the set of inputs.  Because of this, the copy-build-system does not require all the boilerplate code often needed for the trivial-build-system.

     To further simplify the file installation process, an #:install-plan argument is exposed to let the packager specify which files go where.  The install plan is a list of (SOURCE TARGET [FILTERS]).  FILTERS are optional.

       * When SOURCE matches a file or directory without trailing slash, install it to TARGET.

            * If TARGET has a trailing slash, install SOURCE basename beneath TARGET.

            * Otherwise install SOURCE as TARGET.

       * When SOURCE is a directory with a trailing slash, or when FILTERS are used, the trailing slash of TARGET is implied with the same meaning as above.

            * Without FILTERS, install the full SOURCE content to TARGET.

            * With FILTERS among #:include, #:include-regexp, #:exclude, #:exclude-regexp, only select files are installed depending on the filters.  Each filters is specified by a list of strings.

                 * With #:include, install all the files which the path suffix matches at least one of the elements in the given list.

                 * With #:include-regexp, install all the files which the subpaths match at least one of the regular expressions in the given list.

                 * The #:exclude and #:exclude-regexp filters are the complement of their inclusion counterpart.  Without #:include flags, install all files but those matching the exclusion filters. If both inclusions and exclusions are specified, the exclusions are done on top of the inclusions.

          In all cases, the paths relative to SOURCE are preserved within TARGET.

     Examples:

       * ("foo/bar" "share/my-app/"): Install bar to share/my-app/bar.

       * ("foo/bar" "share/my-app/baz"): Install bar to share/my-app/baz.

       * ("foo/" "share/my-app"): Install the content of foo inside share/my-app, e.g., install foo/sub/file to share/my-app/sub/file.

       * ("foo/" "share/my-app" #:include ("sub/file")): Install only foo/sub/file to share/my-app/sub/file.

       * ("foo/sub" "share/my-app" #:include ("file")): Install foo/sub/file to share/my-app/file.

 -- Variable: vim-build-system
     This variable is exported by (guix build-system vim).  It is an extension of the copy-build-system, installing Vim and Neovim plugins into locations where these two text editors know to find their plugins, using their packpaths.

     Packages which are prefixed with vim- will be installed in Vim's packpath, while those prefixed with neovim- will be installed in Neovim's packpath.  If there is a doc directory with the plugin then helptags will be generated automatically.

     There are a couple of keywords added with the vim-build-system:

       * With plugin-name it is possible to set the name of the plugin. While by default this is set to the name and version of the package, it is often more helpful to set this to name which the upstream author calls their plugin.  This is the name used for :packadd from inside Vim.

       * With install-plan it is possible to augment the built-in install-plan of the vim-build-system.  This is particularly helpful if you have files which should be installed in other locations.  For more information about using the install-plan, see the copy-build-system (see copy-build-system).

       * With #:vim it is possible to add this package to Vim's packpath, in addition to if it is added automatically because of the vim- prefix in the package's name.

       * With #:neovim it is possible to add this package to Neovim's packpath, in addition to if it is added automatically because of the neovim- prefix in the package's name.

       * With #:mode it is possible to adjust the path which the plugin is installed into.  By default the plugin is installed into start and other options are available, including opt.  Adding a plugin into opt will mean you will need to run, for example, :packadd foo to load the foo plugin from inside of Vim.

 -- Variable: clojure-build-system
     This variable is exported by (guix build-system clojure).  It implements a simple build procedure for Clojure (https://clojure.org/) packages using plain old compile in Clojure.  Cross-compilation is not supported yet.

     It adds clojure, icedtea and zip to the set of inputs. Different packages can be specified with the #:clojure, #:jdk and #:zip parameters, respectively.

     A list of source directories, test directories and jar names can be specified with the #:source-dirs, #:test-dirs and #:jar-names parameters, respectively.  Compile directory and main class can be specified with the #:compile-dir and #:main-class parameters, respectively. Other parameters are documented below.

     This build system is an extension of ant-build-system, but with the following phases changed:

     build
          This phase calls compile in Clojure to compile source files and runs jar to create jars from both source files and compiled files according to the include list and exclude list specified in #:aot-include and #:aot-exclude, respectively.  The exclude list has priority over the include list.  These lists consist of symbols representing Clojure libraries or the special keyword #:all representing all Clojure libraries found under the source directories.  The parameter #:omit-source? decides if source should be included into the jars.

     check
          This phase runs tests according to the include list and exclude list specified in #:test-include and #:test-exclude, respectively.  Their meanings are analogous to that of #:aot-include and #:aot-exclude, except that the special keyword #:all now stands for all Clojure libraries found under the test directories.  The parameter #:tests? decides if tests should be run.

     install
          This phase installs all jars built previously.

     Apart from the above, this build system also contains an additional phase:

     install-doc
          This phase installs all top-level files with base name matching %doc-regex.  A different regex can be specified with the #:doc-regex parameter.  All files (recursively) inside the documentation directories specified in #:doc-dirs are installed as well.

 -- Variable: cmake-build-system
     This variable is exported by (guix build-system cmake).  It implements the build procedure for packages using the CMake build tool (https://www.cmake.org).

     It automatically adds the cmake package to the set of inputs. Which package is used can be specified with the #:cmake parameter.

     The #:configure-flags parameter is taken as a list of flags passed to the cmake command.  The #:build-type parameter specifies in abstract terms the flags passed to the compiler; it defaults to "RelWithDebInfo" (short for ``release mode with debugging information''), which roughly means that code is compiled with -O2 -g, as is the case for Autoconf-based packages by default.

 -- Variable: composer-build-system
     This variable is exported by (guix build-system composer).  It implements the build procedure for packages using Composer (https://getcomposer.org/), the PHP package manager.

     It automatically adds the php package to the set of inputs.  Which package is used can be specified with the #:php parameter.

     The #:test-target parameter is used to control which script is run for the tests.  By default, the test script is run if it exists.  If the script does not exist, the build system will run phpunit from the source directory, assuming there is a phpunit.xml file.

 -- Variable: dune-build-system
     This variable is exported by (guix build-system dune).  It supports builds of packages using Dune (https://dune.build/), a build tool for the OCaml programming language.  It is implemented as an extension of the ocaml-build-system which is described below.  As such, the #:ocaml and #:findlib parameters can be passed to this build system.

     It automatically adds the dune package to the set of inputs. Which package is used can be specified with the #:dune parameter.

     There is no configure phase because dune packages typically don't need to be configured.  The #:build-flags parameter is taken as a list of flags passed to the dune command during the build.

     The #:jbuild? parameter can be passed to use the jbuild command instead of the more recent dune command while building a package.  Its default value is #f.

     The #:package parameter can be passed to specify a package name, which is useful when a package contains multiple packages and you want to build only one of them.  This is equivalent to passing the -p argument to dune.

 -- Variable: elm-build-system
     This variable is exported by (guix build-system elm).  It implements a build procedure for Elm (https://elm-lang.org) packages similar to elm install.

     The build system adds an Elm compiler package to the set of inputs.  The default compiler package (currently elm-sans-reactor) can be overridden using the #:elm argument.  Additionally, Elm packages needed by the build system itself are added as implicit inputs if they are not already present: to suppress this behavior, use the #:implicit-elm-package-inputs? argument, which is primarily useful for bootstrapping.

     The "dependencies" and "test-dependencies" in an Elm package's elm.json file correspond to propagated-inputs and inputs, respectively.

     Elm requires a particular structure for package names: see Elm Packages for more details, including utilities provided by (guix build-system elm).

     There are currently a few noteworthy limitations to elm-build-system:

       * The build system is focused on packages in the Elm sense of the word: Elm projects which declare { "type": "package" } in their elm.json files.  Using elm-build-system to build Elm applications (which declare { "type": "application" }) is possible, but requires ad-hoc modifications to the build phases.  For examples, see the definitions of the elm-todomvc example application and the elm package itself (because the front-end for the elm reactor command is an Elm application).

       * Elm supports multiple versions of a package coexisting simultaneously under ELM_HOME, but this does not yet work well with elm-build-system. This limitation primarily affects Elm applications, because they specify exact versions for their dependencies, whereas Elm packages specify supported version ranges.  As a workaround, the example applications mentioned above use the patch-application-dependencies procedure provided by (guix build elm-build-system) to rewrite their elm.json files to refer to the package versions actually present in the build environment. Alternatively, Guix package transformations (see Defining Package Variants) could be used to rewrite an application's entire dependency graph.

       * We are not yet able to run tests for Elm projects because neither elm-test-rs (https://github.com/mpizenberg/elm-test-rs) nor the Node.js-based elm-test (https://github.com/rtfeldman/node-test-runner) runner has been packaged for Guix yet.

 -- Variable: go-build-system
     This variable is exported by (guix build-system go).  It implements a build procedure for Go packages using the standard Go build mechanisms (https://golang.org/cmd/go/#hdr-Compile_packages_and_dependencies).

     The user is expected to provide a value for the key #:import-path and, in some cases, #:unpack-path.  The import path (https://golang.org/doc/code.html#ImportPaths) corresponds to the file system path expected by the package's build scripts and any referring packages, and provides a unique way to refer to a Go package.  It is typically based on a combination of the package source code's remote URI and file system hierarchy structure.  In some cases, you will need to unpack the package's source code to a different directory structure than the one indicated by the import path, and #:unpack-path should be used in such cases.

     Packages that provide Go libraries should install their source code into the built output.  The key #:install-source?, which defaults to #t, controls whether or not the source code is installed.  It can be set to #f for packages that only provide executable files.

     Packages can be cross-built, and if a specific architecture or operating system is desired then the keywords #:goarch and #:goos can be used to force the package to be built for that architecture and operating system.  The combinations known to Go can be found in their documentation (https://golang.org/doc/install/source#environment).

     The key #:go can be used to specify the Go compiler package with which to build the package.

 -- Variable: glib-or-gtk-build-system
     This variable is exported by (guix build-system glib-or-gtk).  It is intended for use with packages making use of GLib or GTK+.

     This build system adds the following two phases to the ones defined by gnu-build-system:

     glib-or-gtk-wrap
          The phase glib-or-gtk-wrap ensures that programs in bin/ are able to find GLib ``schemas'' and GTK+ modules (https://developer.gnome.org/gtk3/stable/gtk-running.html).  This is achieved by wrapping the programs in launch scripts that appropriately set the XDG_DATA_DIRS and GTK_PATH environment variables.

          It is possible to exclude specific package outputs from that wrapping process by listing their names in the #:glib-or-gtk-wrap-excluded-outputs parameter.  This is useful when an output is known not to contain any GLib or GTK+ binaries, and where wrapping would gratuitously add a dependency of that output on GLib and GTK+.

     glib-or-gtk-compile-schemas
          The phase glib-or-gtk-compile-schemas makes sure that all GSettings schemas (https://developer.gnome.org/gio/stable/glib-compile-schemas.html) of GLib are compiled.  Compilation is performed by the glib-compile-schemas program.  It is provided by the package glib:bin which is automatically imported by the build system. The glib package providing glib-compile-schemas can be specified with the #:glib parameter.

     Both phases are executed after the install phase.

 -- Variable: guile-build-system
     This build system is for Guile packages that consist exclusively of Scheme code and that are so lean that they don't even have a makefile, let alone a configure script.  It compiles Scheme code using guild compile (see Compilation (GNU Guile Reference Manual)) and installs the .scm and .go files in the right place.  It also installs documentation.

     This build system supports cross-compilation by using the --target option of guild compile.

     Packages built with guile-build-system must provide a Guile package in their native-inputs field.

 -- Variable: julia-build-system
     This variable is exported by (guix build-system julia).  It implements the build procedure used by julia (https://julialang.org/) packages, which essentially is similar to running julia -e 'using Pkg; Pkg.add(package)' in an environment where JULIA_LOAD_PATH contains the paths to all Julia package inputs. Tests are run by calling /test/runtests.jl.

     The Julia package name and uuid is read from the file Project.toml.  These values can be overridden by passing the argument #:julia-package-name (which must be correctly capitalized) or #:julia-package-uuid.

     Julia packages usually manage their binary dependencies via JLLWrappers.jl, a Julia package that creates a module (named after the wrapped library followed by _jll.jl.

     To add the binary path _jll.jl packages, you need to patch the files under src/wrappers/, replacing the call to the macro JLLWrappers.@generate_wrapper_header, adding as a second argument containing the store path the binary.

     As an example, in the MbedTLS Julia package, we add a build phase (see Build Phases) to insert the absolute file name of the wrapped MbedTLS package:

          (add-after 'unpack 'override-binary-path
            (lambda* (#:key inputs #:allow-other-keys)
              (for-each (lambda (wrapper)
                          (substitute* wrapper
                            (("generate_wrapper_header.*")
                             (string-append
                              "generate_wrapper_header(\"MbedTLS\", \""
                              (assoc-ref inputs "mbedtls") "\")\n"))))
                        ;; There's a Julia file for each platform, override them all.
                        (find-files "src/wrappers/" "\\.jl$"))))

     Some older packages that aren't using Project.toml yet, will require this file to be created, too.  It is internally done if the arguments #:julia-package-name and #:julia-package-uuid are provided.

 -- Variable: maven-build-system
     This variable is exported by (guix build-system maven).  It implements a build procedure for Maven (https://maven.apache.org) packages.  Maven is a dependency and lifecycle management tool for Java.  A user of Maven specifies dependencies and plugins in a pom.xml file that Maven reads. When Maven does not have one of the dependencies or plugins in its repository, it will download them and use them to build the package.

     The maven build system ensures that maven will not try to download any dependency by running in offline mode.  Maven will fail if a dependency is missing.  Before running Maven, the pom.xml (and subprojects) are modified to specify the version of dependencies and plugins that match the versions available in the guix build environment.  Dependencies and plugins must be installed in the fake maven repository at lib/m2, and are symlinked into a proper repository before maven is run.  Maven is instructed to use that repository for the build and installs built artifacts there. Changed files are copied to the lib/m2 directory of the package output.

     You can specify a pom.xml file with the #:pom-file argument, or let the build system use the default pom.xml file in the sources.

     In case you need to specify a dependency's version manually, you can use the #:local-packages argument.  It takes an association list where the key is the groupId of the package and its value is an association list where the key is the artifactId of the package and its value is the version you want to override in the pom.xml.

     Some packages use dependencies or plugins that are not useful at runtime nor at build time in Guix.  You can alter the pom.xml file to remove them using the #:exclude argument.  Its value is an association list where the key is the groupId of the plugin or dependency you want to remove, and the value is a list of artifactId you want to remove.

     You can override the default jdk and maven packages with the corresponding argument, #:jdk and #:maven.

     The #:maven-plugins argument is a list of maven plugins used during the build, with the same format as the inputs fields of the package declaration.  Its default value is (default-maven-plugins) which is also exported.

 -- Variable: minetest-mod-build-system
     This variable is exported by (guix build-system minetest).  It implements a build procedure for Minetest (https://www.minetest.net) mods, which consists of copying Lua code, images and other resources to the location Minetest searches for mods.  The build system also minimises PNG images and verifies that Minetest can load the mod without errors.

 -- Variable: minify-build-system
     This variable is exported by (guix build-system minify).  It implements a minification procedure for simple JavaScript packages.

     It adds uglify-js to the set of inputs and uses it to compress all JavaScript files in the src directory.  A different minifier package can be specified with the #:uglify-js parameter, but it is expected that the package writes the minified code to the standard output.

     When the input JavaScript files are not all located in the src directory, the parameter #:javascript-files can be used to specify a list of file names to feed to the minifier.

 -- Variable: mozilla-build-system
     This variable is exported by (guix build-system mozilla).  It sets the --target and --host configuration flags to what software developed by Mozilla expects -- due to historical reasons, Mozilla software expects --host to be the system that is cross-compiled from and --target to be the system that is cross-compiled to, contrary to the standard Autotools conventions.

 -- Variable: ocaml-build-system
     This variable is exported by (guix build-system ocaml).  It implements a build procedure for OCaml (https://ocaml.org) packages, which consists of choosing the correct set of commands to run for each package.  OCaml packages can expect many different commands to be run.  This build system will try some of them.

     When the package has a setup.ml file present at the top-level, it will run ocaml setup.ml -configure, ocaml setup.ml -build and ocaml setup.ml -install.  The build system will assume that this file was generated by OASIS (http://oasis.forge.ocamlcore.org/) and will take care of setting the prefix and enabling tests if they are not disabled.  You can pass configure and build flags with the #:configure-flags and #:build-flags.  The #:test-flags key can be passed to change the set of flags used to enable tests.  The #:use-make? key can be used to bypass this system in the build and install phases.

     When the package has a configure file, it is assumed that it is a hand-made configure script that requires a different argument format than in the gnu-build-system.  You can add more flags with the #:configure-flags key.

     When the package has a Makefile file (or #:use-make? is #t), it will be used and more flags can be passed to the build and install phases with the #:make-flags key.

     Finally, some packages do not have these files and use a somewhat standard location for its build system.  In that case, the build system will run ocaml pkg/pkg.ml or ocaml pkg/build.ml and take care of providing the path to the required findlib module.  Additional flags can be passed via the #:build-flags key.  Install is taken care of by opam-installer.  In this case, the opam package must be added to the native-inputs field of the package definition.

     Note that most OCaml packages assume they will be installed in the same directory as OCaml, which is not what we want in guix.  In particular, they will install .so files in their module's directory, which is usually fine because it is in the OCaml compiler directory.  In guix though, these libraries cannot be found and we use CAML_LD_LIBRARY_PATH.  This variable points to lib/ocaml/site-lib/stubslibs and this is where .so libraries should be installed.

 -- Variable: python-build-system
     This variable is exported by (guix build-system python).  It implements the more or less standard build procedure used by Python packages, which consists in running python setup.py build and then python setup.py install --prefix=/gnu/store/....

     For packages that install stand-alone Python programs under bin/, it takes care of wrapping these programs so that their GUIX_PYTHONPATH environment variable points to all the Python libraries they depend on.

     Which Python package is used to perform the build can be specified with the #:python parameter.  This is a useful way to force a package to be built for a specific version of the Python interpreter, which might be necessary if the package is only compatible with a single interpreter version.

     By default guix calls setup.py under control of setuptools, much like pip does.  Some packages are not compatible with setuptools (and pip), thus you can disable this by setting the #:use-setuptools? parameter to #f.

     If a "python" output is available, the package is installed into it instead of the default "out" output. This is useful for packages that include a Python package as only a part of the software, and thus want to combine the phases of python-build-system with another build system. Python bindings are a common usecase.

 -- Variable: pyproject-build-system
     This is a variable exported by guix build-system pyproject.  It is based on PYTHON-BUILD-SYSTEM, and adds support for pyproject.toml and PEP 517 (https://peps.python.org/pep-0517/). It also supports a variety of build backends and test frameworks.

     The API is slightly different from PYTHON-BUILD-SYSTEM:

       * #:use-setuptools? and #:test-target is removed.

       * #:build-backend is added.  It defaults to #false and will try to guess the appropriate backend based on pyproject.toml.

       * #:test-backend is added.  It defaults to #false and will guess an appropriate test backend based on what is available in package inputs.

       * #:test-flags is added.  The default is '().  These flags are passed as arguments to the test command.  Note that flags for verbose output is always enabled on supported backends.

     It is considered ``experimental'' in that the implementation details are not set in stone yet, however users are encouraged to try it for new Python projects (even those using setup.py).  The API is subject to change, but any breaking changes in the Guix channel will be dealt with.

     Eventually this build system will be deprecated and merged back into PYTHON-BUILD-SYSTEM, probably some time in 2024.

 -- Variable: perl-build-system
     This variable is exported by (guix build-system perl).  It implements the standard build procedure for Perl packages, which either consists in running perl Build.PL --prefix=/gnu/store/..., followed by Build and Build install; or in running perl Makefile.PL PREFIX=/gnu/store/..., followed by make and make install, depending on which of Build.PL or Makefile.PL is present in the package distribution.  Preference is given to the former if both Build.PL and Makefile.PL exist in the package distribution.  This preference can be reversed by specifying #t for the #:make-maker? parameter.

     The initial perl Makefile.PL or perl Build.PL invocation passes flags specified by the #:make-maker-flags or #:module-build-flags parameter, respectively.

     Which Perl package is used can be specified with #:perl.

 -- Variable: renpy-build-system
     This variable is exported by (guix build-system renpy).  It implements the more or less standard build procedure used by Ren'py games, which consists of loading #:game once, thereby creating bytecode for it.

     It further creates a wrapper script in bin/ and a desktop entry in share/applications, both of which can be used to launch the game.

     Which Ren'py package is used can be specified with #:renpy. Games can also be installed in outputs other than ``out'' by using #:output.

 -- Variable: qt-build-system
     This variable is exported by (guix build-system qt).  It is intended for use with applications using Qt or KDE.

     This build system adds the following two phases to the ones defined by cmake-build-system:

     check-setup
          The phase check-setup prepares the environment for running the checks as commonly used by Qt test programs. For now this only sets some environment variables: QT_QPA_PLATFORM=offscreen, DBUS_FATAL_WARNINGS=0 and CTEST_OUTPUT_ON_FAILURE=1.

          This phase is added before the check phase. It's a separate phase to ease adjusting if necessary.

     qt-wrap
          The phase qt-wrap searches for Qt5 plugin paths, QML paths and some XDG in the inputs and output.  In case some path is found, all programs in the output's bin/, sbin/, libexec/ and lib/libexec/ directories are wrapped in scripts defining the necessary environment variables.

          It is possible to exclude specific package outputs from that wrapping process by listing their names in the #:qt-wrap-excluded-outputs parameter. This is useful when an output is known not to contain any Qt binaries, and where wrapping would gratuitously add a dependency of that output on Qt, KDE, or such.

          This phase is added after the install phase.

 -- Variable: r-build-system
     This variable is exported by (guix build-system r).  It implements the build procedure used by R (https://r-project.org) packages, which essentially is little more than running R CMD INSTALL --library=/gnu/store/... in an environment where R_LIBS_SITE contains the paths to all R package inputs.  Tests are run after installation using the R function tools::testInstalledPackage.

 -- Variable: rakudo-build-system
     This variable is exported by (guix build-system rakudo).  It implements the build procedure used by Rakudo (https://rakudo.org/) for Perl6 (https://perl6.org/) packages.  It installs the package to /gnu/store/.../NAME-VERSION/share/perl6 and installs the binaries, library files and the resources, as well as wrap the files under the bin/ directory.  Tests can be skipped by passing #f to the tests? parameter.

     Which rakudo package is used can be specified with rakudo. Which perl6-tap-harness package used for the tests can be specified with #:prove6 or removed by passing #f to the with-prove6? parameter. Which perl6-zef package used for tests and installing can be specified with #:zef or removed by passing #f to the with-zef? parameter.

 -- Variable: rebar-build-system
     This variable is exported by (guix build-system rebar).  It implements a build procedure around rebar3 (https://rebar3.org), a build system for programs written in the Erlang language.

     It adds both rebar3 and the erlang to the set of inputs. Different packages can be specified with the #:rebar and #:erlang parameters, respectively.

     This build system is based on gnu-build-system, but with the following phases changed:

     unpack
          This phase, after unpacking the source like the gnu-build-system does, checks for a file contents.tar.gz at the top-level of the source.  If this file exists, it will be unpacked, too.  This eases handling of package hosted at https://hex.pm/, the Erlang and Elixir package repository.

     bootstrap

     configure
          There are no bootstrap and configure phase because erlang packages typically don’t need to be configured.

     build
          This phase runs rebar3 compile with the flags listed in #:rebar-flags.

     check
          Unless #:tests? #f is passed, this phase runs rebar3 eunit, or some other target specified with #:test-target, with the flags listed in #:rebar-flags,

     install
          This installs the files created in the default profile, or some other profile specified with #:install-profile.

 -- Variable: texlive-build-system
     This variable is exported by (guix build-system texlive).  It is used to build TeX packages in batch mode with a specified engine.  The build system sets the TEXINPUTS variable to find all TeX source files in the inputs.

     By default it tries to run luatex on all .ins files, and if it fails to find any, on all .dtx files.  A different engine and format can be specified with, respectively, the #:tex-engine and #:tex-format arguments.  Different build targets can be specified with the #:build-targets argument, which expects a list of file names.

     It also generates font metrics (i.e., .tfm files) out of Metafont files whenever possible.  Likewise, it can also create TeX formats (i.e., .fmt files) listed in the #:create-formats argument, and generate a symbolic link from bin/ directory to any script located in texmf-dist/scripts/, provided its file name is listed in #:link-scripts argument.

     The build system adds texlive-bin from (gnu packages tex) to the native inputs.  It can be overridden with the #:texlive-bin argument.

     The package texlive-latex-bin, from the same module, contains most of the tools for building TeX Live packages; for convenience, it is also added by default to the native inputs.  However, this can be troublesome when building a dependency of texlive-latex-bin itself.  In this particular situation, the #:texlive-latex-bin? argument should be set to #f.

 -- Variable: ruby-build-system
     This variable is exported by (guix build-system ruby).  It implements the RubyGems build procedure used by Ruby packages, which involves running gem build followed by gem install.

     The source field of a package that uses this build system typically references a gem archive, since this is the format that Ruby developers use when releasing their software.  The build system unpacks the gem archive, potentially patches the source, runs the test suite, repackages the gem, and installs it.  Additionally, directories and tarballs may be referenced to allow building unreleased gems from Git or a traditional source release tarball.

     Which Ruby package is used can be specified with the #:ruby parameter.  A list of additional flags to be passed to the gem command can be specified with the #:gem-flags parameter.

 -- Variable: waf-build-system
     This variable is exported by (guix build-system waf).  It implements a build procedure around the waf script.  The common phases---configure, build, and install---are implemented by passing their names as arguments to the waf script.

     The waf script is executed by the Python interpreter.  Which Python package is used to run the script can be specified with the #:python parameter.

 -- Variable: zig-build-system
     This variable is exported by (guix build-system zig).  It implements the build procedures for the Zig (https://ziglang.org/) build system (zig build command).

     Selecting this build system adds zig to the package inputs, in addition to the packages of gnu-build-system.

     There is no configure phase because Zig packages typically do not need to be configured.  The #:zig-build-flags parameter is a list of flags that are passed to the zig command during the build.  The #:zig-test-flags parameter is a list of flags that are passed to the zig test command during the check phase.  The default compiler package can be overridden with the #:zig argument.

     The optional zig-release-type parameter declares the type of release. Possible values are: safe, fast, or small. The default value is #f, which causes the release flag to be omitted from the zig command.  That results in a debug build.

 -- Variable: scons-build-system
     This variable is exported by (guix build-system scons).  It implements the build procedure used by the SCons software construction tool.  This build system runs scons to build the package, scons test to run tests, and then scons install to install the package.

     Additional flags to be passed to scons can be specified with the #:scons-flags parameter.  The default build and install targets can be overridden with #:build-targets and #:install-targets respectively.  The version of Python used to run SCons can be specified by selecting the appropriate SCons package with the #:scons parameter.

 -- Variable: haskell-build-system
     This variable is exported by (guix build-system haskell).  It implements the Cabal build procedure used by Haskell packages, which involves running runhaskell Setup.hs configure --prefix=/gnu/store/... and runhaskell Setup.hs build. Instead of installing the package by running runhaskell Setup.hs install, to avoid trying to register libraries in the read-only compiler store directory, the build system uses runhaskell Setup.hs copy, followed by runhaskell Setup.hs register.  In addition, the build system generates the package documentation by running runhaskell Setup.hs haddock, unless #:haddock? #f is passed.  Optional Haddock parameters can be passed with the help of the #:haddock-flags parameter.  If the file Setup.hs is not found, the build system looks for Setup.lhs instead.

     Which Haskell compiler is used can be specified with the #:haskell parameter which defaults to ghc.

 -- Variable: dub-build-system
     This variable is exported by (guix build-system dub).  It implements the Dub build procedure used by D packages, which involves running dub build and dub run. Installation is done by copying the files manually.

     Which D compiler is used can be specified with the #:ldc parameter which defaults to ldc.

 -- Variable: emacs-build-system
     This variable is exported by (guix build-system emacs).  It implements an installation procedure similar to the packaging system of Emacs itself (see Packages (The GNU Emacs Manual)).

     It first creates the package-autoloads.el file, then it byte compiles all Emacs Lisp files.  Differently from the Emacs packaging system, the Info documentation files are moved to the standard documentation directory and the dir file is deleted.  The Elisp package files are installed directly under share/emacs/site-lisp.

 -- Variable: font-build-system
     This variable is exported by (guix build-system font).  It implements an installation procedure for font packages where upstream provides pre-compiled TrueType, OpenType, etc. font files that merely need to be copied into place.  It copies font files to standard locations in the output directory.

 -- Variable: meson-build-system
     This variable is exported by (guix build-system meson).  It implements the build procedure for packages that use Meson (https://mesonbuild.com) as their build system.

     It adds both Meson and Ninja (https://ninja-build.org/) to the set of inputs, and they can be changed with the parameters #:meson and #:ninja if needed.

     This build system is an extension of gnu-build-system, but with the following phases changed to some specific for Meson:

     configure
          The phase runs meson with the flags specified in #:configure-flags.  The flag --buildtype is always set to debugoptimized unless something else is specified in #:build-type.

     build
          The phase runs ninja to build the package in parallel by default, but this can be changed with #:parallel-build?.

     check
          The phase runs meson test with a base set of options that cannot be overridden.  This base set of options can be extended via the #:test-options argument, for example to select or skip a specific test suite.

     install
          The phase runs ninja install and can not be changed.

     Apart from that, the build system also adds the following phases:

     fix-runpath
          This phase ensures that all binaries can find the libraries they need. It searches for required libraries in subdirectories of the package being built, and adds those to RUNPATH where needed.  It also removes references to libraries left over from the build phase by meson, such as test dependencies, that aren't actually required for the program to run.

     glib-or-gtk-wrap
          This phase is the phase provided by glib-or-gtk-build-system, and it is not enabled by default.  It can be enabled with #:glib-or-gtk?.

     glib-or-gtk-compile-schemas
          This phase is the phase provided by glib-or-gtk-build-system, and it is not enabled by default.  It can be enabled with #:glib-or-gtk?.

 -- Variable: linux-module-build-system
     linux-module-build-system allows building Linux kernel modules.

     This build system is an extension of gnu-build-system, but with the following phases changed:

     configure
          This phase configures the environment so that the Linux kernel's Makefile can be used to build the external kernel module.

     build
          This phase uses the Linux kernel's Makefile in order to build the external kernel module.

     install
          This phase uses the Linux kernel's Makefile in order to install the external kernel module.

     It is possible and useful to specify the Linux kernel to use for building the module (in the arguments form of a package using the linux-module-build-system, use the key #:linux to specify it).

 -- Variable: node-build-system
     This variable is exported by (guix build-system node).  It implements the build procedure used by Node.js (https://nodejs.org), which implements an approximation of the npm install command, followed by an npm test command.

     Which Node.js package is used to interpret the npm commands can be specified with the #:node parameter which defaults to node.

 -- Variable: tree-sitter-build-system

     This variable is exported by (guix build-system tree-sitter).  It implements procedures to compile grammars for the Tree-sitter (https://tree-sitter.github.io/tree-sitter/) parsing library.  It essentially runs tree-sitter generate to translate grammar.js grammars to JSON and then to C.  Which it then compiles to native code.

     Tree-sitter packages may support multiple grammars, so this build system supports a #:grammar-directories keyword to specify a list of locations where a grammar.js file may be found.

     Grammars sometimes depend on each other, such as C++ depending on C and TypeScript depending on JavaScript.  You may use inputs to declare such dependencies.

Lastly, for packages that do not need anything as sophisticated, a ``trivial'' build system is provided.  It is trivial in the sense that it provides basically no support: it does not pull any implicit inputs, and does not have a notion of build phases.

 -- Variable: trivial-build-system
     This variable is exported by (guix build-system trivial).

     This build system requires a #:builder argument.  This argument must be a Scheme expression that builds the package output(s)---as with build-expression->derivation (see build-expression->derivation).

 -- Variable: channel-build-system
     This variable is exported by (guix build-system channel).

     This build system is meant primarily for internal use.  A package using this build system must have a channel specification as its source field (see Channels); alternatively, its source can be a directory name, in which case an additional #:commit argument must be supplied to specify the commit being built (a hexadecimal string).

     The resulting package is a Guix instance of the given channel, similar to how guix time-machine would build it.

Build Phases
============

Almost all package build systems implement a notion build phases: a sequence of actions that the build system executes, when you build the package, leading to the installed byproducts in the store.  A notable exception is the ``bare-bones'' trivial-build-system (see Build Systems).

As discussed in the previous section, those build systems provide a standard list of phases.  For gnu-build-system, the main build phases are the following:

set-paths
     Define search path environment variables for all the input packages, including PATH (see Search Paths).

unpack
     Unpack the source tarball, and change the current directory to the extracted source tree.  If the source is actually a directory, copy it to the build tree, and enter that directory.

patch-source-shebangs
     Patch shebangs encountered in source files so they refer to the right store file names.  For instance, this changes #!/bin/sh to #!/gnu/store/...-bash-4.3/bin/sh.

configure
     Run the configure script with a number of default options, such as --prefix=/gnu/store/..., as well as the options specified by the #:configure-flags argument.

build
     Run make with the list of flags specified with #:make-flags.  If the #:parallel-build? argument is true (the default), build with make -j.

check
     Run make check, or some other target specified with #:test-target, unless #:tests? #f is passed.  If the #:parallel-tests? argument is true (the default), run make check -j.

install
     Run make install with the flags listed in #:make-flags.

patch-shebangs
     Patch shebangs on the installed executable files.

strip
     Strip debugging symbols from ELF files (unless #:strip-binaries? is false), copying them to the debug output when available (see Installing Debugging Files).

validate-runpath
     Validate the RUNPATH of ELF binaries, unless #:validate-runpath? is false (see Build Systems).

     This validation step consists in making sure that all the shared libraries needed by an ELF binary, which are listed as DT_NEEDED entries in its PT_DYNAMIC segment, appear in the DT_RUNPATH entry of that binary.  In other words, it ensures that running or using those binaries will not result in a ``file not found'' error at run time.  See -rpath (The GNU Linker), for more information on RUNPATH.

Other build systems have similar phases, with some variations.  For example, cmake-build-system has same-named phases but its configure phases runs cmake instead of ./configure. Others, such as python-build-system, have a wholly different list of standard phases.  All this code runs on the build side: it is evaluated when you actually build the package, in a dedicated build process spawned by the build daemon (see Invoking guix-daemon).

Build phases are represented as association lists or ``alists'' (see Association Lists (GNU Guile Reference Manual)) where each key is a symbol for the name of the phase and the associated value is a procedure that accepts an arbitrary number of arguments.  By convention, those procedures receive information about the build in the form of keyword parameters, which they can use or ignore.

For example, here is how (guix build gnu-build-system) defines %standard-phases, the variable holding its alist of build phases (We present a simplified view of those build phases, but do take a look at (guix build gnu-build-system) to see all the details!):

     ;; The build phases of 'gnu-build-system'.

     (define* (unpack #:key source #:allow-other-keys)
       ;; Extract the source tarball.
       (invoke "tar" "xvf" source))

     (define* (configure #:key outputs #:allow-other-keys)
       ;; Run the 'configure' script.  Install to output "out".
       (let ((out (assoc-ref outputs "out")))
         (invoke "./configure"
                 (string-append "--prefix=" out))))

     (define* (build #:allow-other-keys)
       ;; Compile.
       (invoke "make"))

     (define* (check #:key (test-target "check") (tests? #true)
                     #:allow-other-keys)
       ;; Run the test suite.
       (if tests?
           (invoke "make" test-target)
           (display "test suite not run\n")))

     (define* (install #:allow-other-keys)
       ;; Install files to the prefix 'configure' specified.
       (invoke "make" "install"))

     (define %standard-phases
       ;; The list of standard phases (quite a few are omitted
       ;; for brevity).  Each element is a symbol/procedure pair.
       (list (cons 'unpack unpack)
             (cons 'configure configure)
             (cons 'build build)
             (cons 'check check)
             (cons 'install install)))

This shows how %standard-phases is defined as a list of symbol/procedure pairs (see Pairs (GNU Guile Reference Manual)).  The first pair associates the unpack procedure with the unpack symbol---a name; the second pair defines the configure phase similarly, and so on.  When building a package that uses gnu-build-system with its default list of phases, those phases are executed sequentially.  You can see the name of each phase started and completed in the build log of packages that you build.

Let's now look at the procedures themselves.  Each one is defined with define*: #:key lists keyword parameters the procedure accepts, possibly with a default value, and #:allow-other-keys specifies that other keyword parameters are ignored (see Optional Arguments (GNU Guile Reference Manual)).

The unpack procedure honors the source parameter, which the build system uses to pass the file name of the source tarball (or version control checkout), and it ignores other parameters.  The configure phase only cares about the outputs parameter, an alist mapping package output names to their store file name (see Packages with Multiple Outputs).  It extracts the file name of for out, the default output, and passes it to ./configure as the installation prefix, meaning that make install will eventually copy all the files in that directory (see configuration and makefile conventions (GNU Coding Standards)).  build and install ignore all their arguments.  check honors the test-target argument, which specifies the name of the Makefile target to run tests; it prints a message and skips tests when tests? is false.

The list of phases used for a particular package can be changed with the #:phases parameter of the build system.  Changing the set of build phases boils down to building a new alist of phases based on the %standard-phases alist described above.  This can be done with standard alist procedures such as alist-delete (see SRFI-1 Association Lists (GNU Guile Reference Manual)); however, it is more convenient to do so with modify-phases (see modify-phases).

Here is an example of a package definition that removes the configure phase of %standard-phases and inserts a new phase before the build phase, called set-prefix-in-makefile:

     (define-public example
       (package
         (name "example")
         ;; other fields omitted
         (build-system gnu-build-system)
         (arguments
          (list
           #:phases
           #~(modify-phases %standard-phases
               (delete 'configure)
               (add-before 'build 'set-prefix-in-makefile
                 (lambda* (#:key inputs #:allow-other-keys)
                   ;; Modify the makefile so that its
                   ;; 'PREFIX' variable points to #$output and
                   ;; 'XMLLINT' points to the correct path.
                   (substitute* "Makefile"
                     (("PREFIX =.*")
                      (string-append "PREFIX = " #$output "\n"))
                     (("XMLLINT =.*")
                      (string-append "XMLLINT = "
                                     (search-input-file inputs "/bin/xmllint")
                                     "\n"))))))))))

The new phase that is inserted is written as an anonymous procedure, introduced with lambda*; it looks for the xmllint executable under a /bin directory among the package's inputs (see package Reference).  It also honors the outputs parameter we have seen before.  See Build Utilities, for more about the helpers used by this phase, and for more examples of modify-phases.

     You can inspect the code associated with a package's #:phases argument interactively, at the REPL (see Using Guix Interactively).

Keep in mind that build phases are code evaluated at the time the package is actually built.  This explains why the whole modify-phases expression above is quoted (it comes after the ' or apostrophe): it is staged for later execution. See G-Expressions, for an explanation of code staging and the code strata involved.

Build Utilities
===============

As soon as you start writing non-trivial package definitions (see Defining Packages) or other build actions (see G-Expressions), you will likely start looking for helpers for ``shell-like'' actions---creating directories, copying and deleting files recursively, manipulating build phases, and so on.  The (guix build utils) module provides such utility procedures.

Most build systems load (guix build utils) (see Build Systems).  Thus, when writing custom build phases for your package definitions, you can usually assume those procedures are in scope.

When writing G-expressions, you can import (guix build utils) on the ``build side'' using with-imported-modules and then put it in scope with the use-modules form (see Using Guile Modules (GNU Guile Reference Manual)):

     (with-imported-modules '((guix build utils))  ;import it
       (computed-file "empty-tree"
                      #~(begin
                          ;; Put it in scope.
                          (use-modules (guix build utils))

                          ;; Happily use its 'mkdir-p' procedure.
                          (mkdir-p (string-append #$output "/a/b/c")))))

The remainder of this section is the reference for most of the utility procedures provided by (guix build utils).

Dealing with Store File Names
-----------------------------

This section documents procedures that deal with store file names.

 -- Procedure: %store-directory
     Return the directory name of the store.

 -- Procedure: store-file-name? file
     Return true if FILE is in the store.

 -- Procedure: strip-store-file-name file
     Strip the /gnu/store and hash from FILE, a store file name. The result is typically a "PACKAGE-VERSION" string.

 -- Procedure: package-name->name+version name
     Given NAME, a package name like "foo-0.9.1b", return two values: "foo" and "0.9.1b".  When the version part is unavailable, NAME and #f are returned.  The first hyphen followed by a digit is considered to introduce the version part.

File Types
----------

The procedures below deal with files and file types.

 -- Procedure: directory-exists? dir
     Return #t if DIR exists and is a directory.

 -- Procedure: executable-file? file
     Return #t if FILE exists and is executable.

 -- Procedure: symbolic-link? file
     Return #t if FILE is a symbolic link (aka. a ``symlink'').

 -- Procedure: elf-file? file
 -- Procedure: ar-file? file
 -- Procedure: gzip-file? file
     Return #t if FILE is, respectively, an ELF file, an ar archive (such as a .a static library), or a gzip file.

 -- Procedure: reset-gzip-timestamp file [#:keep-mtime? #t]
     If FILE is a gzip file, reset its embedded timestamp (as with gzip --no-name) and return true.  Otherwise return #f. When KEEP-MTIME? is true, preserve FILE's modification time.

File Manipulation
-----------------

The following procedures and macros help create, modify, and delete files.  They provide functionality comparable to common shell utilities such as mkdir -p, cp -r, rm -r, and sed.  They complement Guile's extensive, but low-level, file system interface (see POSIX (GNU Guile Reference Manual)).

 -- Macro: with-directory-excursion directory body ...
     Run BODY with DIRECTORY as the process's current directory.

     Essentially, this macro changes the current directory to DIRECTORY before evaluating BODY, using chdir (see Processes (GNU Guile Reference Manual)).  It changes back to the initial directory when the dynamic extent of BODY is left, be it via normal procedure return or via a non-local exit such as an exception.

 -- Procedure: mkdir-p dir
     Create directory DIR and all its ancestors.

 -- Procedure: install-file file directory
     Create DIRECTORY if it does not exist and copy FILE in there under the same name.

 -- Procedure: make-file-writable file
     Make FILE writable for its owner.

 -- Procedure: copy-recursively source destination
     [#:log (current-output-port)] [#:follow-symlinks? #f]
     [#:copy-file copy-file] [#:keep-mtime? #f] [#:keep-permissions? #t]
     Copy SOURCE directory to DESTINATION.  Follow symlinks if FOLLOW-SYMLINKS?  is true; otherwise, just preserve them.  Call COPY-FILE to copy regular files.  When KEEP-MTIME? is true, keep the modification time of the files in SOURCE on those of DESTINATION.  When KEEP-PERMISSIONS? is true, preserve file permissions.  Write verbose output to the LOG port.

 -- Procedure: delete-file-recursively dir [#:follow-mounts? #f]
     Delete DIR recursively, like rm -rf, without following symlinks.  Don't follow mount points either, unless FOLLOW-MOUNTS? is true.  Report but ignore errors.

 -- Macro: substitute* file
     ((regexp match-var...) body...) ...
     Substitute REGEXP in FILE by the string returned by BODY.  BODY is evaluated with each MATCH-VAR bound to the corresponding positional regexp sub-expression.  For example:

          (substitute* file
            (("hello")
             "good morning\n")
            (("foo([a-z]+)bar(.*)$" all letters end)
             (string-append "baz" letters end)))

     Here, anytime a line of FILE contains hello, it is replaced by good morning.  Anytime a line of FILE matches the second regexp, all is bound to the complete match, letters is bound to the first sub-expression, and end is bound to the last one.

     When one of the MATCH-VAR is _, no variable is bound to the corresponding match substring.

     Alternatively, FILE may be a list of file names, in which case they are all subject to the substitutions.

     Be careful about using $ to match the end of a line; by itself it won't match the terminating newline of a line.  For example, to match a whole line ending with a backslash, one needs a regex like "(.*)\\\\\n$".

File Search
-----------

This section documents procedures to search and filter files.

 -- Procedure: file-name-predicate regexp
     Return a predicate that returns true when passed a file name whose base name matches REGEXP.

 -- Procedure: find-files dir [pred]
     [#:stat lstat] [#:directories? #f] [#:fail-on-error? #f]
     Return the lexicographically sorted list of files under DIR for which PRED returns true.  PRED is passed two arguments: the absolute file name, and its stat buffer; the default predicate always returns true.  PRED can also be a regular expression, in which case it is equivalent to (file-name-predicate PRED). STAT is used to obtain file information; using lstat means that symlinks are not followed.  If DIRECTORIES? is true, then directories will also be included.  If FAIL-ON-ERROR? is true, raise an exception upon error.

Here are a few examples where we assume that the current directory is the root of the Guix source tree:

     ;; List all the regular files in the current directory.
     (find-files ".")
     => ("./.dir-locals.el" "./.gitignore" ...)

     ;; List all the .scm files under gnu/services.
     (find-files "gnu/services" "\\.scm$")
     => ("gnu/services/admin.scm" "gnu/services/audio.scm" ...)

     ;; List ar files in the current directory.
     (find-files "." (lambda (file stat) (ar-file? file)))
     => ("./libformat.a" "./libstore.a" ...)

 -- Procedure: which program
     Return the complete file name for PROGRAM as found in $PATH, or #f if PROGRAM could not be found.

 -- Procedure: search-input-file inputs name
 -- Procedure: search-input-directory inputs name
     Return the complete file name for NAME as found in INPUTS; search-input-file searches for a regular file and search-input-directory searches for a directory.  If NAME could not be found, an exception is raised.

     Here, INPUTS must be an association list like inputs and native-inputs as available to build phases (see Build Phases).

Here is a (simplified) example of how search-input-file is used in a build phase of the wireguard-tools package:

     (add-after 'install 'wrap-wg-quick
       (lambda* (#:key inputs outputs #:allow-other-keys)
         (let ((coreutils (string-append (assoc-ref inputs "coreutils")
                                         "/bin")))
           (wrap-program (search-input-file outputs "bin/wg-quick")
             #:sh (search-input-file inputs "bin/bash")
             `("PATH" ":" prefix ,(list coreutils))))))

Program Invocation
------------------

You'll find handy procedures to spawn processes in this module, essentially convenient wrappers around Guile's system* (see system* (GNU Guile Reference Manual)).

 -- Procedure: invoke program args...
     Invoke PROGRAM with the given ARGS.  Raise an &invoke-error exception if the exit code is non-zero; otherwise return #t.

     The advantage compared to system* is that you do not need to check the return value.  This reduces boilerplate in shell-script-like snippets for instance in package build phases.

 -- Procedure: invoke-error? c
     Return true if C is an &invoke-error condition.

 -- Procedure: invoke-error-program c
 -- Procedure: invoke-error-arguments c
 -- Procedure: invoke-error-exit-status c
 -- Procedure: invoke-error-term-signal c
 -- Procedure: invoke-error-stop-signal c
     Access specific fields of C, an &invoke-error condition.

 -- Procedure: report-invoke-error c [port]
     Report to PORT (by default the current error port) about C, an &invoke-error condition, in a human-friendly way.

     Typical usage would look like this:

          (use-modules (srfi srfi-34) ;for 'guard'
                       (guix build utils))

          (guard (c ((invoke-error? c)
                     (report-invoke-error c)))
            (invoke "date" "--imaginary-option"))

          -| command "date" "--imaginary-option" failed with status 1

 -- Procedure: invoke/quiet program args...
     Invoke PROGRAM with ARGS and capture PROGRAM's standard output and standard error.  If PROGRAM succeeds, print nothing and return the unspecified value; otherwise, raise a &message error condition that includes the status code and the output of PROGRAM.

     Here's an example:

          (use-modules (srfi srfi-34) ;for 'guard'
                       (srfi srfi-35) ;for 'message-condition?'
                       (guix build utils))

          (guard (c ((message-condition? c)
                     (display (condition-message c))))
            (invoke/quiet "date")  ;all is fine
            (invoke/quiet "date" "--imaginary-option"))

          -| 'date --imaginary-option' exited with status 1; output follows:

              date: unrecognized option '--imaginary-option'
              Try 'date --help' for more information.

Build Phases
------------

The (guix build utils) also contains tools to manipulate build phases as used by build systems (see Build Systems).  Build phases are represented as association lists or ``alists'' (see Association Lists (GNU Guile Reference Manual)) where each key is a symbol naming the phase and the associated value is a procedure (see Build Phases).

Guile core and the (srfi srfi-1) module both provide tools to manipulate alists.  The (guix build utils) module complements those with tools written with build phases in mind.

 -- Macro: modify-phases phases clause...
     Modify PHASES sequentially as per each CLAUSE, which may have one of the following forms:

          (delete OLD-PHASE-NAME)
          (replace OLD-PHASE-NAME NEW-PHASE)
          (add-before OLD-PHASE-NAME NEW-PHASE-NAME NEW-PHASE)
          (add-after OLD-PHASE-NAME NEW-PHASE-NAME NEW-PHASE)

     Where every PHASE-NAME above is an expression evaluating to a symbol, and NEW-PHASE an expression evaluating to a procedure.

The example below is taken from the definition of the grep package.  It adds a phase to run after the install phase, called fix-egrep-and-fgrep.  That phase is a procedure (lambda* is for anonymous procedures) that takes a #:outputs keyword argument and ignores extra keyword arguments (see Optional Arguments (GNU Guile Reference Manual), for more on lambda* and optional and keyword arguments.)  The phase uses substitute* to modify the installed egrep and fgrep scripts so that they refer to grep by its absolute file name:

     (modify-phases %standard-phases
       (add-after 'install 'fix-egrep-and-fgrep
         ;; Patch 'egrep' and 'fgrep' to execute 'grep' via its
         ;; absolute file name instead of searching for it in $PATH.
         (lambda* (#:key outputs #:allow-other-keys)
           (let* ((out (assoc-ref outputs "out"))
                  (bin (string-append out "/bin")))
             (substitute* (list (string-append bin "/egrep")
                                (string-append bin "/fgrep"))
               (("^exec grep")
                (string-append "exec " bin "/grep")))))))

In the example below, phases are modified in two ways: the standard configure phase is deleted, presumably because the package does not have a configure script or anything similar, and the default install phase is replaced by one that manually copies the executable files to be installed:

     (modify-phases %standard-phases
       (delete 'configure)      ;no 'configure' script
       (replace 'install
         (lambda* (#:key outputs #:allow-other-keys)
           ;; The package's Makefile doesn't provide an "install"
           ;; rule so do it by ourselves.
           (let ((bin (string-append (assoc-ref outputs "out")
                                     "/bin")))
             (install-file "footswitch" bin)
             (install-file "scythe" bin)))))

Wrappers
--------

It is not unusual for a command to require certain environment variables to be set for proper functioning, typically search paths (see Search Paths).  Failing to do that, the command might fail to find files or other commands it relies on, or it might pick the ``wrong'' ones---depending on the environment in which it runs.  Examples include:

  * a shell script that assumes all the commands it uses are in PATH;

  * a Guile program that assumes all its modules are in GUILE_LOAD_PATH and GUILE_LOAD_COMPILED_PATH;

  * a Qt application that expects to find certain plugins in QT_PLUGIN_PATH.

For a package writer, the goal is to make sure commands always work the same rather than depend on some external settings.  One way to achieve that is to wrap commands in a thin script that sets those environment variables, thereby ensuring that those run-time dependencies are always found.  The wrapper would be used to set PATH, GUILE_LOAD_PATH, or QT_PLUGIN_PATH in the examples above.

To ease that task, the (guix build utils) module provides a couple of helpers to wrap commands.

 -- Procedure: wrap-program program [#:sh sh] [#:rest variables]
     Make a wrapper for PROGRAM.  VARIABLES should look like this:

          '(VARIABLE DELIMITER POSITION LIST-OF-DIRECTORIES)

     where DELIMITER is optional.  : will be used if DELIMITER is not given.

     For example, this call:

          (wrap-program "foo"
                        '("PATH" ":" = ("/gnu/.../bar/bin"))
                        '("CERT_PATH" suffix ("/gnu/.../baz/certs"
                                              "/qux/certs")))

     will copy foo to .foo-real and create the file foo with the following contents:

          #!location/of/bin/bash
          export PATH="/gnu/.../bar/bin"
          export CERT_PATH="$CERT_PATH${CERT_PATH:+:}/gnu/.../baz/certs:/qux/certs"
          exec -a $0 location/of/.foo-real "$@"

     If PROGRAM has previously been wrapped by wrap-program, the wrapper is extended with definitions for VARIABLES.  If it is not, SH will be used as the interpreter.

 -- Procedure: wrap-script program [#:guile guile] [#:rest variables]
     Wrap the script PROGRAM such that VARIABLES are set first. The format of VARIABLES is the same as in the wrap-program procedure.  This procedure differs from wrap-program in that it does not create a separate shell script.  Instead, PROGRAM is modified directly by prepending a Guile script, which is interpreted as a comment in the script's language.

     Special encoding comments as supported by Python are recreated on the second line.

     Note that this procedure can only be used once per file as Guile scripts are not supported.

Search Paths
============

Many programs and libraries look for input data in a search path, a list of directories: shells like Bash look for executables in the command search path, a C compiler looks for .h files in its header search path, the Python interpreter looks for .py files in its search path, the spell checker has a search path for dictionaries, and so on.

Search paths can usually be defined or overridden via environment variables (see Environment Variables (The GNU C Library Reference Manual)).  For example, the search paths mentioned above can be changed by defining the PATH, C_INCLUDE_PATH, PYTHONPATH (or GUIX_PYTHONPATH), and DICPATH environment variables---you know, all these something-PATH variables that you need to get right or things ``won't be found''.

You may have noticed from the command line that Guix ``knows'' which search path environment variables should be defined, and how.  When you install packages in your default profile, the file ~/.guix-profile/etc/profile is created, which you can ``source'' from the shell to set those variables.  Likewise, if you ask guix shell to create an environment containing Python and NumPy, a Python library, and if you pass it the --search-paths option, it will tell you about PATH and GUIX_PYTHONPATH (see Invoking guix shell):

     $ guix shell python python-numpy --pure --search-paths
     export PATH="/gnu/store/...-profile/bin"
     export GUIX_PYTHONPATH="/gnu/store/...-profile/lib/python3.9/site-packages"

When you omit --search-paths, it defines these environment variables right away, such that Python can readily find NumPy:

     $ guix shell python python-numpy -- python3
     Python 3.9.6 (default, Jan  1 1970, 00:00:01)
     [GCC 10.3.0] on linux
     Type "help", "copyright", "credits" or "license" for more information.
     >>> import numpy
     >>> numpy.version.version
     '1.20.3'

For this to work, the definition of the python package declares the search path it cares about and its associated environment variable, GUIX_PYTHONPATH.  It looks like this:

     (package
       (name "python")
       (version "3.9.9")
       ;; some fields omitted...
       (native-search-paths
        (list (search-path-specification
               (variable "GUIX_PYTHONPATH")
               (files (list "lib/python/3.9/site-packages"))))))

What this native-search-paths field says is that, when the python package is used, the GUIX_PYTHONPATH environment variable must be defined to include all the lib/python/3.9/site-packages sub-directories encountered in its environment.  (The native- bit means that, if we are in a cross-compilation environment, only native inputs may be added to the search path; see search-paths.) In the NumPy example above, the profile where python appears contains exactly one such sub-directory, and GUIX_PYTHONPATH is set to that.  When there are several lib/python/3.9/site-packages---this is the case in package build environments---they are all added to GUIX_PYTHONPATH, separated by colons (:).

     Notice that GUIX_PYTHONPATH is specified as part of the definition of the python package, and not as part of that of python-numpy.  This is because this environment variable ``belongs'' to Python, not NumPy: Python actually reads the value of that variable and honors it.

     Corollary: if you create a profile that does not contain python, GUIX_PYTHONPATH will not be defined, even if it contains packages that provide .py files:

          $ guix shell python-numpy --search-paths --pure
          export PATH="/gnu/store/...-profile/bin"

     This makes a lot of sense if we look at this profile in isolation: no software in this profile would read GUIX_PYTHONPATH.

Of course, there are many variations on that theme: some packages honor more than one search path, some use separators other than colon, some accumulate several directories in their search path, and so on.  A more complex example is the search path of libxml2: the value of the XML_CATALOG_FILES environment variable is space-separated, it must contain a list of catalog.xml files (not directories), which are to be found in xml sub-directories---nothing less.  The search path specification looks like this:

     (package
       (name "libxml2")
       ;; some fields omitted
       (native-search-paths
        (list (search-path-specification
               (variable "XML_CATALOG_FILES")
               (separator " ")
               (files '("xml"))
               (file-pattern "^catalog\\.xml$")
               (file-type 'regular)))))

Worry not, search path specifications are usually not this tricky.

The (guix search-paths) module defines the data type of search path specifications and a number of helper procedures.  Below is the reference of search path specifications.

 -- Data Type: search-path-specification
     The data type for search path specifications.

     variable
          The name of the environment variable for this search path (a string).

     files
          The list of sub-directories (strings) that should be added to the search path.

     separator (default: ":")
          The string used to separate search path components.

          As a special case, a separator value of #f specifies a ``single-component search path''---in other words, a search path that cannot contain more than one element.  This is useful in some cases, such as the SSL_CERT_DIR variable (honored by OpenSSL, cURL, and a few other packages) or the ASPELL_DICT_DIR variable (honored by the GNU Aspell spell checker), both of which must point to a single directory.

     file-type (default: 'directory)
          The type of file being matched---'directory or 'regular, though it can be any symbol returned by stat:type (see stat (GNU Guile Reference Manual)).

          In the libxml2 example above, we would match regular files; in the Python example, we would match directories.

     file-pattern (default: #f)
          This must be either #f or a regular expression specifying files to be matched within the sub-directories specified by the files field.

          Again, the libxml2 example shows a situation where this is needed.

Some search paths are not tied by a single package but to many packages. To reduce duplications, some of them are pre-defined in (guix search-paths).

 -- Variable: $SSL_CERT_DIR
 -- Variable: $SSL_CERT_FILE
     These two search paths indicate where X.509 certificates can be found (see X.509 Certificates).

These pre-defined search paths can be used as in the following example:

     (package
       (name "curl")
       ;; some fields omitted ...
       (native-search-paths (list $SSL_CERT_DIR $SSL_CERT_FILE)))

How do you turn search path specifications on one hand and a bunch of directories on the other hand in a set of environment variable definitions?  That's the job of evaluate-search-paths.

 -- Procedure: evaluate-search-paths search-paths directories [getenv]
     Evaluate SEARCH-PATHS, a list of search-path specifications, for DIRECTORIES, a list of directory names, and return a list of specification/value pairs.  Use GETENV to determine the current settings and report only settings not already effective.

The (guix profiles) provides a higher-level helper procedure, load-profile, that sets the environment variables of a profile.

The Store
=========

Conceptually, the store is the place where derivations that have been built successfully are stored---by default, /gnu/store. Sub-directories in the store are referred to as store items or sometimes store paths.  The store has an associated database that contains information such as the store paths referred to by each store path, and the list of valid store items---results of successful builds.  This database resides in LOCALSTATEDIR/guix/db, where LOCALSTATEDIR is the state directory specified via --localstatedir at configure time, usually /var.

The store is always accessed by the daemon on behalf of its clients (see Invoking guix-daemon).  To manipulate the store, clients connect to the daemon over a Unix-domain socket, send requests to it, and read the result---these are remote procedure calls, or RPCs.

     Users must never modify files under /gnu/store directly. This would lead to inconsistencies and break the immutability assumptions of Guix's functional model (see Introduction).

     See guix gc --verify, for information on how to check the integrity of the store and attempt recovery from accidental modifications.

The (guix store) module provides procedures to connect to the daemon, and to perform RPCs.  These are described below.  By default, open-connection, and thus all the guix commands, connect to the local daemon or to the URI specified by the GUIX_DAEMON_SOCKET environment variable.

 -- Environment Variable: GUIX_DAEMON_SOCKET
     When set, the value of this variable should be a file name or a URI designating the daemon endpoint.  When it is a file name, it denotes a Unix-domain socket to connect to.  In addition to file names, the supported URI schemes are:

     file
     unix
          These are for Unix-domain sockets. file:///var/guix/daemon-socket/socket is equivalent to /var/guix/daemon-socket/socket.

     guix
          These URIs denote connections over TCP/IP, without encryption nor authentication of the remote host.  The URI must specify the host name and optionally a port number (by default port 44146 is used):

               guix://master.guix.example.org:1234

          This setup is suitable on local networks, such as clusters, where only trusted nodes may connect to the build daemon at master.guix.example.org.

          The --listen option of guix-daemon can be used to instruct it to listen for TCP connections (see --listen).

     ssh
          These URIs allow you to connect to a remote daemon over SSH.  This feature requires Guile-SSH (see Requirements) and a working guile binary in PATH on the destination machine.  It supports public key and GSSAPI authentication.  A typical URL might look like this:

               ssh://charlie@guix.example.org:22

          As for guix copy, the usual OpenSSH client configuration files are honored (see Invoking guix copy).

     Additional URI schemes may be supported in the future.

          The ability to connect to remote build daemons is considered experimental as of VERSION.  Please get in touch with us to share any problems or suggestions you may have (see Contributing).

 -- Procedure: open-connection [uri] [#:reserve-space? #t]
     Connect to the daemon over the Unix-domain socket at URI (a string).  When RESERVE-SPACE? is true, instruct it to reserve a little bit of extra space on the file system so that the garbage collector can still operate should the disk become full.  Return a server object.

     FILE defaults to %default-socket-path, which is the normal location given the options that were passed to configure.

 -- Procedure: close-connection server
     Close the connection to SERVER.

 -- Variable: current-build-output-port
     This variable is bound to a SRFI-39 parameter, which refers to the port where build and error logs sent by the daemon should be written.

Procedures that make RPCs all take a server object as their first argument.

 -- Procedure: valid-path? server path
     Return #t when PATH designates a valid store item and #f otherwise (an invalid item may exist on disk but still be invalid, for instance because it is the result of an aborted or failed build).

     A &store-protocol-error condition is raised if PATH is not prefixed by the store directory (/gnu/store).

 -- Procedure: add-text-to-store server name text [references]
     Add TEXT under file NAME in the store, and return its store path.  REFERENCES is the list of store paths referred to by the resulting store path.

 -- Procedure: build-derivations store derivations [mode]
     Build DERIVATIONS, a list of <derivation> objects, .drv file names, or derivation/output pairs, using the specified MODE---(build-mode normal) by default.

Note that the (guix monads) module provides a monad as well as monadic versions of the above procedures, with the goal of making it more convenient to work with code that accesses the store (see The Store Monad).

This section is currently incomplete.

Derivations
===========

Low-level build actions and the environment in which they are performed are represented by derivations.  A derivation contains the following pieces of information:

  * The outputs of the derivation---derivations produce at least one file or directory in the store, but may produce more.

  * The inputs of the derivation---i.e., its build-time dependencies---which may be other derivations or plain files in the store (patches, build scripts, etc.).

  * The system type targeted by the derivation---e.g., x86_64-linux.

  * The file name of a build script in the store, along with the arguments to be passed.

  * A list of environment variables to be defined.

Derivations allow clients of the daemon to communicate build actions to the store.  They exist in two forms: as an in-memory representation, both on the client- and daemon-side, and as files in the store whose name end in .drv---these files are referred to as derivation paths.  Derivations paths can be passed to the build-derivations procedure to perform the build actions they prescribe (see The Store).

Operations such as file downloads and version-control checkouts for which the expected content hash is known in advance are modeled as fixed-output derivations.  Unlike regular derivations, the outputs of a fixed-output derivation are independent of its inputs---e.g., a source code download produces the same result regardless of the download method and tools being used.

The outputs of derivations---i.e., the build results---have a set of references, as reported by the references RPC or the guix gc --references command (see Invoking guix gc).  References are the set of run-time dependencies of the build results.  References are a subset of the inputs of the derivation; this subset is automatically computed by the build daemon by scanning all the files in the outputs.

The (guix derivations) module provides a representation of derivations as Scheme objects, along with procedures to create and otherwise manipulate derivations.  The lowest-level primitive to create a derivation is the derivation procedure:

 -- Procedure: derivation store name builder args
     [#:outputs '("out")] [#:hash #f] [#:hash-algo #f]
     [#:recursive? #f] [#:inputs '()] [#:env-vars '()]
     [#:system (%current-system)] [#:references-graphs #f]
     [#:allowed-references #f] [#:disallowed-references #f]
     [#:leaked-env-vars #f] [#:local-build? #f]
     [#:substitutable? #t] [#:properties '()]
     Build a derivation with the given arguments, and return the resulting <derivation> object.

     When HASH and HASH-ALGO are given, a fixed-output derivation is created---i.e., one whose result is known in advance, such as a file download.  If, in addition, RECURSIVE? is true, then that fixed output may be an executable file or a directory and HASH must be the hash of an archive containing this output.

     When REFERENCES-GRAPHS is true, it must be a list of file name/store path pairs.  In that case, the reference graph of each store path is exported in the build environment in the corresponding file, in a simple text format.

     When ALLOWED-REFERENCES is true, it must be a list of store items or outputs that the derivation's output may refer to.  Likewise, DISALLOWED-REFERENCES, if true, must be a list of things the outputs may not refer to.

     When LEAKED-ENV-VARS is true, it must be a list of strings denoting environment variables that are allowed to ``leak'' from the daemon's environment to the build environment.  This is only applicable to fixed-output derivations---i.e., when HASH is true.  The main use is to allow variables such as http_proxy to be passed to derivations that download files.

     When LOCAL-BUILD? is true, declare that the derivation is not a good candidate for offloading and should rather be built locally (see Daemon Offload Setup).  This is the case for small derivations where the costs of data transfers would outweigh the benefits.

     When SUBSTITUTABLE? is false, declare that substitutes of the derivation's output should not be used (see Substitutes).  This is useful, for instance, when building packages that capture details of the host CPU instruction set.

     PROPERTIES must be an association list describing ``properties'' of the derivation.  It is kept as-is, uninterpreted, in the derivation.

Here's an example with a shell script as its builder, assuming STORE is an open connection to the daemon, and BASH points to a Bash executable in the store:

     (use-modules (guix utils)
                  (guix store)
                  (guix derivations))

     (let ((builder   ; add the Bash script to the store
             (add-text-to-store store "my-builder.sh"
                                "echo hello world > $out\n" '())))
       (derivation store "foo"
                   bash `("-e" ,builder)
                   #:inputs `((,bash) (,builder))
                   #:env-vars '(("HOME" . "/homeless"))))
     => #<derivation /gnu/store/...-foo.drv => /gnu/store/...-foo>

As can be guessed, this primitive is cumbersome to use directly.  A better approach is to write build scripts in Scheme, of course!  The best course of action for that is to write the build code as a ``G-expression'', and to pass it to gexp->derivation.  For more information, see G-Expressions.

Once upon a time, gexp->derivation did not exist and constructing derivations with build code written in Scheme was achieved with build-expression->derivation, documented below.  This procedure is now deprecated in favor of the much nicer gexp->derivation.

 -- Procedure: build-expression->derivation store name exp
     [#:system (%current-system)] [#:inputs '()]
     [#:outputs '("out")] [#:hash #f] [#:hash-algo #f]
     [#:recursive? #f] [#:env-vars '()] [#:modules '()]
     [#:references-graphs #f] [#:allowed-references #f]
     [#:disallowed-references #f]
     [#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f]
     Return a derivation that executes Scheme expression EXP as a builder for derivation NAME.  INPUTS must be a list of (name drv-path sub-drv) tuples; when SUB-DRV is omitted, "out" is assumed.  MODULES is a list of names of Guile modules from the current search path to be copied in the store, compiled, and made available in the load path during the execution of EXP---e.g., ((guix build utils) (guix build gnu-build-system)).

     EXP is evaluated in an environment where %outputs is bound to a list of output/path pairs, and where %build-inputs is bound to a list of string/output-path pairs made from INPUTS. Optionally, ENV-VARS is a list of string pairs specifying the name and value of environment variables visible to the builder.  The builder terminates by passing the result of EXP to exit; thus, when EXP returns #f, the build is considered to have failed.

     EXP is built using GUILE-FOR-BUILD (a derivation).  When GUILE-FOR-BUILD is omitted or is #f, the value of the %guile-for-build fluid is used instead.

     See the derivation procedure for the meaning of REFERENCES-GRAPHS, ALLOWED-REFERENCES, DISALLOWED-REFERENCES, LOCAL-BUILD?, and SUBSTITUTABLE?.

Here's an example of a single-output derivation that creates a directory containing one file:

     (let ((builder '(let ((out (assoc-ref %outputs "out")))
                       (mkdir out)    ; create /gnu/store/...-goo
                       (call-with-output-file (string-append out "/test")
                         (lambda (p)
                           (display '(hello guix) p))))))
       (build-expression->derivation store "goo" builder))

     => #<derivation /gnu/store/...-goo.drv => ...>

The Store Monad
===============

The procedures that operate on the store described in the previous sections all take an open connection to the build daemon as their first argument.  Although the underlying model is functional, they either have side effects or depend on the current state of the store.

The former is inconvenient: the connection to the build daemon has to be carried around in all those functions, making it impossible to compose functions that do not take that parameter with functions that do.  The latter can be problematic: since store operations have side effects and/or depend on external state, they have to be properly sequenced.

This is where the (guix monads) module comes in.  This module provides a framework for working with monads, and a particularly useful monad for our uses, the store monad.  Monads are a construct that allows two things: associating ``context'' with values (in our case, the context is the store), and building sequences of computations (here computations include accesses to the store).  Values in a monad---values that carry this additional context---are called monadic values; procedures that return such values are called monadic procedures.

Consider this ``normal'' procedure:

     (define (sh-symlink store)
       ;; Return a derivation that symlinks the 'bash' executable.
       (let* ((drv (package-derivation store bash))
              (out (derivation->output-path drv))
              (sh  (string-append out "/bin/bash")))
         (build-expression->derivation store "sh"
                                       `(symlink ,sh %output))))

Using (guix monads) and (guix gexp), it may be rewritten as a monadic function:

     (define (sh-symlink)
       ;; Same, but return a monadic value.
       (mlet %store-monad ((drv (package->derivation bash)))
         (gexp->derivation "sh"
                           #~(symlink (string-append #$drv "/bin/bash")
                                      #$output))))

There are several things to note in the second version: the store parameter is now implicit and is ``threaded'' in the calls to the package->derivation and gexp->derivation monadic procedures, and the monadic value returned by package->derivation is bound using mlet instead of plain let.

As it turns out, the call to package->derivation can even be omitted since it will take place implicitly, as we will see later (see G-Expressions):

     (define (sh-symlink)
       (gexp->derivation "sh"
                         #~(symlink (string-append #$bash "/bin/bash")
                                    #$output)))

Calling the monadic sh-symlink has no effect.  As someone once said, ``you exit a monad like you exit a building on fire: by running''. So, to exit the monad and get the desired effect, one must use run-with-store:

     (run-with-store (open-connection) (sh-symlink))
     => /gnu/store/...-sh-symlink

Note that the (guix monad-repl) module extends the Guile REPL with new ``commands'' to make it easier to deal with monadic procedures: run-in-store, and enter-store-monad (see Using Guix Interactively).  The former is used to ``run'' a single monadic value through the store:

     scheme@(guile-user)> ,run-in-store (package->derivation hello)
     $1 = #<derivation /gnu/store/...-hello-2.9.drv => ...>

The latter enters a recursive REPL, where all the return values are automatically run through the store:

     scheme@(guile-user)> ,enter-store-monad
     store-monad@(guile-user) [1]> (package->derivation hello)
     $2 = #<derivation /gnu/store/...-hello-2.9.drv => ...>
     store-monad@(guile-user) [1]> (text-file "foo" "Hello!")
     $3 = "/gnu/store/...-foo"
     store-monad@(guile-user) [1]> ,q
     scheme@(guile-user)>

Note that non-monadic values cannot be returned in the store-monad REPL.

Other meta-commands are available at the REPL, such as ,build to build a file-like object (see Using Guix Interactively).

The main syntactic forms to deal with monads in general are provided by the (guix monads) module and are described below.

 -- Macro: with-monad monad body ...
     Evaluate any >>= or return forms in BODY as being in MONAD.

 -- Macro: return val
     Return a monadic value that encapsulates VAL.

 -- Macro: >>= mval mproc ...
     Bind monadic value MVAL, passing its ``contents'' to monadic procedures MPROC... (This operation is commonly referred to as ``bind'', but that name denotes an unrelated procedure in Guile.  Thus we use this somewhat cryptic symbol inherited from the Haskell language.).  There can be one MPROC or several of them, as in this example:

          (run-with-state
              (with-monad %state-monad
                (>>= (return 1)
                     (lambda (x) (return (+ 1 x)))
                     (lambda (x) (return (* 2 x)))))
            'some-state)

          => 4
          => some-state

 -- Macro: mlet monad ((var mval) ...) body ...
 -- Macro: mlet* monad ((var mval) ...) body ...
     Bind the variables VAR to the monadic values MVAL in BODY, which is a sequence of expressions.  As with the bind operator, this can be thought of as ``unpacking'' the raw, non-monadic value ``contained'' in MVAL and making VAR refer to that raw, non-monadic value within the scope of the BODY.  The form (VAR -> VAL) binds VAR to the ``normal'' value VAL, as per let.  The binding operations occur in sequence from left to right.  The last expression of BODY must be a monadic expression, and its result will become the result of the mlet or mlet* when run in the MONAD.

     mlet* is to mlet what let* is to let (see Local Bindings (GNU Guile Reference Manual)).

 -- Macro: mbegin monad mexp ...
     Bind MEXP and the following monadic expressions in sequence, returning the result of the last expression.  Every expression in the sequence must be a monadic expression.

     This is akin to mlet, except that the return values of the monadic expressions are ignored.  In that sense, it is analogous to begin, but applied to monadic expressions.

 -- Macro: mwhen condition mexp0 mexp* ...
     When CONDITION is true, evaluate the sequence of monadic expressions MEXP0..MEXP* as in an mbegin.  When CONDITION is false, return *unspecified* in the current monad.  Every expression in the sequence must be a monadic expression.

 -- Macro: munless condition mexp0 mexp* ...
     When CONDITION is false, evaluate the sequence of monadic expressions MEXP0..MEXP* as in an mbegin.  When CONDITION is true, return *unspecified* in the current monad.  Every expression in the sequence must be a monadic expression.

The (guix monads) module provides the state monad, which allows an additional value---the state---to be threaded through monadic procedure calls.

 -- Variable: %state-monad
     The state monad.  Procedures in the state monad can access and change the state that is threaded.

     Consider the example below.  The square procedure returns a value in the state monad.  It returns the square of its argument, but also increments the current state value:

          (define (square x)
            (mlet %state-monad ((count (current-state)))
              (mbegin %state-monad
                (set-current-state (+ 1 count))
                (return (* x x)))))

          (run-with-state (sequence %state-monad (map square (iota 3))) 0)
          => (0 1 4)
          => 3

     When ``run'' through %state-monad, we obtain that additional state value, which is the number of square calls.

 -- Monadic Procedure: current-state
     Return the current state as a monadic value.

 -- Monadic Procedure: set-current-state VALUE
     Set the current state to VALUE and return the previous state as a monadic value.

 -- Monadic Procedure: state-push VALUE
     Push VALUE to the current state, which is assumed to be a list, and return the previous state as a monadic value.

 -- Monadic Procedure: state-pop
     Pop a value from the current state and return it as a monadic value. The state is assumed to be a list.

 -- Procedure: run-with-state mval [state]
     Run monadic value MVAL starting with STATE as the initial state.  Return two values: the resulting value, and the resulting state.

The main interface to the store monad, provided by the (guix store) module, is as follows.

 -- Variable: %store-monad
     The store monad---an alias for %state-monad.

     Values in the store monad encapsulate accesses to the store.  When its effect is needed, a value of the store monad must be ``evaluated'' by passing it to the run-with-store procedure (see below).

 -- Procedure: run-with-store store mval
     [#:guile-for-build] [#:system (%current-system)]
     Run MVAL, a monadic value in the store monad, in STORE, an open store connection.

 -- Monadic Procedure: text-file NAME TEXT [REFERENCES]
     Return as a monadic value the absolute file name in the store of the file containing TEXT, a string.  REFERENCES is a list of store items that the resulting text file refers to; it defaults to the empty list.

 -- Monadic Procedure: binary-file NAME DATA [REFERENCES]
     Return as a monadic value the absolute file name in the store of the file containing DATA, a bytevector.  REFERENCES is a list of store items that the resulting binary file refers to; it defaults to the empty list.

 -- Monadic Procedure: interned-file FILE [NAME]
     [#:recursive? #t] [#:select? (const #t)]
     Return the name of FILE once interned in the store.  Use NAME as its store name, or the basename of FILE if NAME is omitted.

     When RECURSIVE? is true, the contents of FILE are added recursively; if FILE designates a flat file and RECURSIVE? is true, its contents are added, and its permission bits are kept.

     When RECURSIVE? is true, call (SELECT? FILE STAT) for each directory entry, where FILE is the entry's absolute file name and STAT is the result of lstat; exclude entries for which SELECT? does not return true.

     The example below adds a file to the store, under two different names:

          (run-with-store (open-connection)
            (mlet %store-monad ((a (interned-file "README"))
                                (b (interned-file "README" "LEGU-MIN")))
              (return (list a b))))

          => ("/gnu/store/rwm...-README" "/gnu/store/44i...-LEGU-MIN")

The (guix packages) module exports the following package-related monadic procedures:

 -- Monadic Procedure: package-file PACKAGE [FILE]
     [#:system (%current-system)] [#:target #f]
     [#:output "out"]
     Return as a monadic value in the absolute file name of FILE within the OUTPUT directory of PACKAGE.  When FILE is omitted, return the name of the OUTPUT directory of PACKAGE.  When TARGET is true, use it as a cross-compilation target triplet.

     Note that this procedure does not build PACKAGE.  Thus, the result might or might not designate an existing file.  We recommend not using this procedure unless you know what you are doing.

 -- Monadic Procedure: package->derivation PACKAGE [SYSTEM]
 -- Monadic Procedure: package->cross-derivation PACKAGE
     TARGET [SYSTEM]
     Monadic version of package-derivation and package-cross-derivation (see Defining Packages).

G-Expressions
=============

So we have ``derivations'', which represent a sequence of build actions to be performed to produce an item in the store (see Derivations). These build actions are performed when asking the daemon to actually build the derivations; they are run by the daemon in a container (see Invoking guix-daemon).

It should come as no surprise that we like to write these build actions in Scheme.  When we do that, we end up with two strata of Scheme code (The term stratum in this context was coined by Manuel Serrano et al. in the context of their work on Hop.  Oleg Kiselyov, who has written insightful essays and code on this topic (http://okmij.org/ftp/meta-programming/#meta-scheme), refers to this kind of code generation as staging.): the ``host code''---code that defines packages, talks to the daemon, etc.---and the ``build code''---code that actually performs build actions, such as making directories, invoking make, and so on (see Build Phases).

To describe a derivation and its build actions, one typically needs to embed build code inside host code.  It boils down to manipulating build code as data, and the homoiconicity of Scheme---code has a direct representation as data---comes in handy for that.  But we need more than the normal quasiquote mechanism in Scheme to construct build expressions.

The (guix gexp) module implements G-expressions, a form of S-expressions adapted to build expressions.  G-expressions, or gexps, consist essentially of three syntactic forms: gexp, ungexp, and ungexp-splicing (or simply: #~, #$, and #$@), which are comparable to quasiquote, unquote, and unquote-splicing, respectively (see quasiquote (GNU Guile Reference Manual)).  However, there are major differences:

  * Gexps are meant to be written to a file and run or manipulated by other processes.

  * When a high-level object such as a package or derivation is unquoted inside a gexp, the result is as if its output file name had been introduced.

  * Gexps carry information about the packages or derivations they refer to, and these dependencies are automatically added as inputs to the build processes that use them.

This mechanism is not limited to package and derivation objects: compilers able to ``lower'' other high-level objects to derivations or files in the store can be defined, such that these objects can also be inserted into gexps.  For example, a useful type of high-level objects that can be inserted in a gexp is ``file-like objects'', which make it easy to add files to the store and to refer to them in derivations and such (see local-file and plain-file below).

To illustrate the idea, here is an example of a gexp:

     (define build-exp
       #~(begin
           (mkdir #$output)
           (chdir #$output)
           (symlink (string-append #$coreutils "/bin/ls")
                    "list-files")))

This gexp can be passed to gexp->derivation; we obtain a derivation that builds a directory containing exactly one symlink to /gnu/store/...-coreutils-8.22/bin/ls:

     (gexp->derivation "the-thing" build-exp)

As one would expect, the "/gnu/store/...-coreutils-8.22" string is substituted to the reference to the COREUTILS package in the actual build code, and COREUTILS is automatically made an input to the derivation.  Likewise, #$output (equivalent to (ungexp output)) is replaced by a string containing the directory name of the output of the derivation.

In a cross-compilation context, it is useful to distinguish between references to the native build of a package---that can run on the host---versus references to cross builds of a package.  To that end, the #+ plays the same role as #$, but is a reference to a native package build:

     (gexp->derivation "vi"
        #~(begin
            (mkdir #$output)
            (mkdir (string-append #$output "/bin"))
            (system* (string-append #+coreutils "/bin/ln")
                     "-s"
                     (string-append #$emacs "/bin/emacs")
                     (string-append #$output "/bin/vi")))
        #:target "aarch64-linux-gnu")

In the example above, the native build of COREUTILS is used, so that ln can actually run on the host; but then the cross-compiled build of EMACS is referenced.

Another gexp feature is imported modules: sometimes you want to be able to use certain Guile modules from the ``host environment'' in the gexp, so those modules should be imported in the ``build environment''. The with-imported-modules form allows you to express that:

     (let ((build (with-imported-modules '((guix build utils))
                    #~(begin
                        (use-modules (guix build utils))
                        (mkdir-p (string-append #$output "/bin"))))))
       (gexp->derivation "empty-dir"
                         #~(begin
                             #$build
                             (display "success!\n")
                             #t)))

In this example, the (guix build utils) module is automatically pulled into the isolated build environment of our gexp, such that (use-modules (guix build utils)) works as expected.

Usually you want the closure of the module to be imported---i.e., the module itself and all the modules it depends on---rather than just the module; failing to do that, attempts to use the module will fail because of missing dependent modules.  The source-module-closure procedure computes the closure of a module by looking at its source file headers, which comes in handy in this case:

     (use-modules (guix modules))   ;for 'source-module-closure'

     (with-imported-modules (source-module-closure
                              '((guix build utils)
                                (gnu build image)))
       (gexp->derivation "something-with-vms"
                         #~(begin
                             (use-modules (guix build utils)
                                          (gnu build image))
                             ...)))

In the same vein, sometimes you want to import not just pure-Scheme modules, but also ``extensions'' such as Guile bindings to C libraries or other ``full-blown'' packages.  Say you need the guile-json package available on the build side, here's how you would do it:

     (use-modules (gnu packages guile))  ;for 'guile-json'

     (with-extensions (list guile-json)
       (gexp->derivation "something-with-json"
                         #~(begin
                             (use-modules (json))
                             ...)))

The syntactic form to construct gexps is summarized below.

 -- Macro: #~EXP
 -- Macro: (gexp EXP)
     Return a G-expression containing EXP.  EXP may contain one or more of the following forms:

     #$OBJ
     (ungexp OBJ)
          Introduce a reference to OBJ.  OBJ may have one of the supported types, for example a package or a derivation, in which case the ungexp form is replaced by its output file name---e.g., "/gnu/store/...-coreutils-8.22.

          If OBJ is a list, it is traversed and references to supported objects are substituted similarly.

          If OBJ is another gexp, its contents are inserted and its dependencies are added to those of the containing gexp.

          If OBJ is another kind of object, it is inserted as is.

     #$OBJ:OUTPUT
     (ungexp OBJ OUTPUT)
          This is like the form above, but referring explicitly to the OUTPUT of OBJ---this is useful when OBJ produces multiple outputs (see Packages with Multiple Outputs).

          Sometimes a gexp unconditionally refers to the "out" output, but the user of that gexp would still like to insert a reference to another output.  The gexp-input procedure aims to address that. See gexp-input.

     #+OBJ
     #+OBJ:output
     (ungexp-native OBJ)
     (ungexp-native OBJ OUTPUT)
          Same as ungexp, but produces a reference to the native build of OBJ when used in a cross compilation context.

     #$output[:OUTPUT]
     (ungexp output [OUTPUT])
          Insert a reference to derivation output OUTPUT, or to the main output when OUTPUT is omitted.

          This only makes sense for gexps passed to gexp->derivation.

     #$@LST
     (ungexp-splicing LST)
          Like the above, but splices the contents of LST inside the containing list.

     #+@LST
     (ungexp-native-splicing LST)
          Like the above, but refers to native builds of the objects listed in LST.

     G-expressions created by gexp or #~ are run-time objects of the gexp? type (see below).

 -- Macro: with-imported-modules modules body...
     Mark the gexps defined in BODY... as requiring MODULES in their execution environment.

     Each item in MODULES can be the name of a module, such as (guix build utils), or it can be a module name, followed by an arrow, followed by a file-like object:

          `((guix build utils)
            (guix gcrypt)
            ((guix config) => ,(scheme-file "config.scm"
                                            #~(define-module ...))))

     In the example above, the first two modules are taken from the search path, and the last one is created from the given file-like object.

     This form has lexical scope: it has an effect on the gexps directly defined in BODY..., but not on those defined, say, in procedures called from BODY....

 -- Macro: with-extensions extensions body...
     Mark the gexps defined in BODY... as requiring EXTENSIONS in their build and execution environment. EXTENSIONS is typically a list of package objects such as those defined in the (gnu packages guile) module.

     Concretely, the packages listed in EXTENSIONS are added to the load path while compiling imported modules in BODY...; they are also added to the load path of the gexp returned by BODY....

 -- Procedure: gexp? obj
     Return #t if OBJ is a G-expression.

G-expressions are meant to be written to disk, either as code building some derivation, or as plain files in the store.  The monadic procedures below allow you to do that (see The Store Monad, for more information about monads).

 -- Monadic Procedure: gexp->derivation NAME EXP
     [#:system (%current-system)] [#:target #f] [#:graft? #t]
     [#:hash #f] [#:hash-algo #f]
     [#:recursive? #f] [#:env-vars '()] [#:modules '()]
     [#:module-path %load-path]
     [#:effective-version "2.2"]
     [#:references-graphs #f] [#:allowed-references #f]
     [#:disallowed-references #f]
     [#:leaked-env-vars #f]
     [#:script-name (string-append NAME "-builder")]
     [#:deprecation-warnings #f]
     [#:local-build? #f] [#:substitutable? #t]
     [#:properties '()] [#:guile-for-build #f]
     Return a derivation NAME that runs EXP (a gexp) with GUILE-FOR-BUILD (a derivation) on SYSTEM; EXP is stored in a file called SCRIPT-NAME.  When TARGET is true, it is used as the cross-compilation target triplet for packages referred to by EXP.

     MODULES is deprecated in favor of with-imported-modules. Its meaning is to make MODULES available in the evaluation context of EXP; MODULES is a list of names of Guile modules searched in MODULE-PATH to be copied in the store, compiled, and made available in the load path during the execution of EXP---e.g., ((guix build utils) (guix build gnu-build-system)).

     EFFECTIVE-VERSION determines the string to use when adding extensions of EXP (see with-extensions) to the search path---e.g., "2.2".

     GRAFT? determines whether packages referred to by EXP should be grafted when applicable.

     When REFERENCES-GRAPHS is true, it must be a list of tuples of one of the following forms:

          (FILE-NAME OBJ)
          (FILE-NAME OBJ OUTPUT)
          (FILE-NAME GEXP-INPUT)
          (FILE-NAME STORE-ITEM)

     The right-hand-side of each element of REFERENCES-GRAPHS is automatically made an input of the build process of EXP.  In the build environment, each FILE-NAME contains the reference graph of the corresponding item, in a simple text format.

     ALLOWED-REFERENCES must be either #f or a list of output names and packages. In the latter case, the list denotes store items that the result is allowed to refer to.  Any reference to another store item will lead to a build error. Similarly for DISALLOWED-REFERENCES, which can list items that must not be referenced by the outputs.

     DEPRECATION-WARNINGS determines whether to show deprecation warnings while compiling modules.  It can be #f, #t, or 'detailed.

     The other arguments are as for derivation (see Derivations).

The local-file, plain-file, computed-file, program-file, and scheme-file procedures below return file-like objects.  That is, when unquoted in a G-expression, these objects lead to a file in the store.  Consider this G-expression:

     #~(system* #$(file-append glibc "/sbin/nscd") "-f"
                #$(local-file "/tmp/my-nscd.conf"))

The effect here is to ``intern'' /tmp/my-nscd.conf by copying it to the store.  Once expanded, for instance via gexp->derivation, the G-expression refers to that copy under /gnu/store; thus, modifying or removing the file in /tmp does not have any effect on what the G-expression does. plain-file can be used similarly; it differs in that the file content is directly passed as a string.

 -- Procedure: local-file file [name] [#:recursive? #f] [#:select? (const #t)]
     Return an object representing local file FILE to add to the store; this object can be used in a gexp.  If FILE is a literal string denoting a relative file name, it is looked up relative to the source file where it appears; if FILE is not a literal string, it is looked up relative to the current working directory at run time. FILE will be added to the store under NAME--by default the base name of FILE.

     When RECURSIVE? is true, the contents of FILE are added recursively; if FILE designates a flat file and RECURSIVE? is true, its contents are added, and its permission bits are kept.

     When RECURSIVE? is true, call (SELECT? FILE STAT) for each directory entry, where FILE is the entry's absolute file name and STAT is the result of lstat; exclude entries for which SELECT? does not return true.

     This is the declarative counterpart of the interned-file monadic procedure (see interned-file).

 -- Procedure: plain-file name content
     Return an object representing a text file called NAME with the given CONTENT (a string or a bytevector) to be added to the store.

     This is the declarative counterpart of text-file.

 -- Procedure: computed-file name gexp [#:local-build? #t] [#:options '()]
     Return an object representing the store item NAME, a file or directory computed by GEXP.  When LOCAL-BUILD? is true (the default), the derivation is built locally.  OPTIONS is a list of additional arguments to pass to gexp->derivation.

     This is the declarative counterpart of gexp->derivation.

 -- Monadic Procedure: gexp->script NAME EXP
     [#:guile (default-guile)] [#:module-path %load-path]
     [#:system (%current-system)] [#:target #f]
     Return an executable script NAME that runs EXP using GUILE, with EXP's imported modules in its search path. Look up EXP's modules in MODULE-PATH.

     The example below builds a script that simply invokes the ls command:

          (use-modules (guix gexp) (gnu packages base))

          (gexp->script "list-files"
                        #~(execl #$(file-append coreutils "/bin/ls")
                                 "ls"))

     When ``running'' it through the store (see run-with-store), we obtain a derivation that produces an executable file /gnu/store/...-list-files along these lines:

          #!/gnu/store/...-guile-2.0.11/bin/guile -ds
          !#
          (execl "/gnu/store/...-coreutils-8.22"/bin/ls" "ls")

 -- Procedure: program-file name exp [#:guile #f] [#:module-path %load-path]
     Return an object representing the executable store item NAME that runs GEXP.  GUILE is the Guile package used to execute that script.  Imported modules of GEXP are looked up in MODULE-PATH.

     This is the declarative counterpart of gexp->script.

 -- Monadic Procedure: gexp->file NAME EXP
     [#:set-load-path? #t] [#:module-path %load-path]
     [#:splice? #f]
     [#:guile (default-guile)]
     Return a derivation that builds a file NAME containing EXP. When SPLICE?  is true, EXP is considered to be a list of expressions that will be spliced in the resulting file.

     When SET-LOAD-PATH? is true, emit code in the resulting file to set %load-path and %load-compiled-path to honor EXP's imported modules.  Look up EXP's modules in MODULE-PATH.

     The resulting file holds references to all the dependencies of EXP or a subset thereof.

 -- Procedure: scheme-file name exp [#:splice? #f] [#:set-load-path? #t]
     Return an object representing the Scheme file NAME that contains EXP.

     This is the declarative counterpart of gexp->file.

 -- Monadic Procedure: text-file* NAME TEXT ...
     Return as a monadic value a derivation that builds a text file containing all of TEXT.  TEXT may list, in addition to strings, objects of any type that can be used in a gexp: packages, derivations, local file objects, etc.  The resulting store file holds references to all these.

     This variant should be preferred over text-file anytime the file to create will reference items from the store.  This is typically the case when building a configuration file that embeds store file names, like this:

          (define (profile.sh)
            ;; Return the name of a shell script in the store that
            ;; initializes the 'PATH' environment variable.
            (text-file* "profile.sh"
                        "export PATH=" coreutils "/bin:"
                        grep "/bin:" sed "/bin\n"))

     In this example, the resulting /gnu/store/...-profile.sh file will reference COREUTILS, GREP, and SED, thereby preventing them from being garbage-collected during its lifetime.

 -- Procedure: mixed-text-file name text ...
     Return an object representing store file NAME containing TEXT.  TEXT is a sequence of strings and file-like objects, as in:

          (mixed-text-file "profile"
                           "export PATH=" coreutils "/bin:" grep "/bin")

     This is the declarative counterpart of text-file*.

 -- Procedure: file-union name files
     Return a <computed-file> that builds a directory containing all of FILES. Each item in FILES must be a two-element list where the first element is the file name to use in the new directory, and the second element is a gexp denoting the target file.  Here's an example:

          (file-union "etc"
                      `(("hosts" ,(plain-file "hosts"
                                              "127.0.0.1 localhost"))
                        ("bashrc" ,(plain-file "bashrc"
                                               "alias ls='ls --color=auto'"))))

     This yields an etc directory containing these two files.

 -- Procedure: directory-union name things
     Return a directory that is the union of THINGS, where THINGS is a list of file-like objects denoting directories.  For example:

          (directory-union "guile+emacs" (list guile emacs))

     yields a directory that is the union of the guile and emacs packages.

 -- Procedure: file-append obj suffix ...
     Return a file-like object that expands to the concatenation of OBJ and SUFFIX, where OBJ is a lowerable object and each SUFFIX is a string.

     As an example, consider this gexp:

          (gexp->script "run-uname"
                        #~(system* #$(file-append coreutils
                                                  "/bin/uname")))

     The same effect could be achieved with:

          (gexp->script "run-uname"
                        #~(system* (string-append #$coreutils
                                                  "/bin/uname")))

     There is one difference though: in the file-append case, the resulting script contains the absolute file name as a string, whereas in the second case, the resulting script contains a (string-append ...) expression to construct the file name at run time.

 -- Macro: let-system system body...
 -- Macro: let-system (system target) body...
     Bind SYSTEM to the currently targeted system---e.g., "x86_64-linux"---within BODY.

     In the second case, additionally bind TARGET to the current cross-compilation target---a GNU triplet such as "arm-linux-gnueabihf"---or #f if we are not cross-compiling.

     let-system is useful in the occasional case where the object spliced into the gexp depends on the target system, as in this example:

          #~(system*
             #+(let-system system
                 (cond ((string-prefix? "armhf-" system)
                        (file-append qemu "/bin/qemu-system-arm"))
                       ((string-prefix? "x86_64-" system)
                        (file-append qemu "/bin/qemu-system-x86_64"))
                       (else
                        (error "dunno!"))))
             "-net" "user" #$image)

 -- Macro: with-parameters ((parameter value) ...) exp
     This macro is similar to the parameterize form for dynamically-bound parameters (see Parameters (GNU Guile Reference Manual)).  The key difference is that it takes effect when the file-like object returned by EXP is lowered to a derivation or store item.

     A typical use of with-parameters is to force the system in effect for a given object:

          (with-parameters ((%current-system "i686-linux"))
            coreutils)

     The example above returns an object that corresponds to the i686 build of Coreutils, regardless of the current value of %current-system.

 -- Procedure: gexp-input OBJ [OUTPUT] [#:native? #f]
     Return a gexp input record for the given OUTPUT of file-like object OBJ, with #:native? determining whether this is a native reference (as with ungexp-native) or not.

     This procedure is helpful when you want to pass a reference to a specific output of an object to some procedure that may not know about that output.  For example, assume you have this procedure, which takes one file-like object:

          (define (make-symlink target)
            (computed-file "the-symlink"
                           #~(symlink #$target #$output)))

     Here make-symlink can only ever refer to the default output of TARGET---the "out" output (see Packages with Multiple Outputs).  To have it refer to, say, the "lib" output of the hwloc package, you can call it like so:

          (make-symlink (gexp-input hwloc "lib"))

     You can also compose it like any other file-like object:

          (make-symlink
            (file-append (gexp-input hwloc "lib") "/lib/libhwloc.so"))

Of course, in addition to gexps embedded in ``host'' code, there are also modules containing build tools.  To make it clear that they are meant to be used in the build stratum, these modules are kept in the (guix build ...) name space.

Internally, high-level objects are lowered, using their compiler, to either derivations or store items.  For instance, lowering a package yields a derivation, and lowering a plain-file yields a store item.  This is achieved using the lower-object monadic procedure.

 -- Monadic Procedure: lower-object OBJ [SYSTEM]
     [#:target #f]
     Return as a value in %store-monad the derivation or store item corresponding to OBJ for SYSTEM, cross-compiling for TARGET if TARGET is true.  OBJ must be an object that has an associated gexp compiler, such as a <package>.

 -- Procedure: gexp->approximate-sexp gexp
     Sometimes, it may be useful to convert a G-exp into a S-exp.  For example, some linters (see Invoking guix lint) peek into the build phases of a package to detect potential problems.  This conversion can be achieved with this procedure.  However, some information can be lost in the process.  More specifically, lowerable objects will be silently replaced with some arbitrary object -- currently the list (*approximate*), but this may change.

Invoking guix repl
==================

The guix repl command makes it easier to program Guix in Guile by launching a Guile read-eval-print loop (REPL) for interactive programming (see Using Guile Interactively (GNU Guile Reference Manual)), or by running Guile scripts (see Running Guile Scripts (GNU Guile Reference Manual)). Compared to just launching the guile command, guix repl guarantees that all the Guix modules and all its dependencies are available in the search path.

The general syntax is:

     guix repl OPTIONS [FILE ARGS]

When a FILE argument is provided, FILE is executed as a Guile scripts:

     guix repl my-script.scm

To pass arguments to the script, use -- to prevent them from being interpreted as arguments to guix repl itself:

     guix repl -- my-script.scm --input=foo.txt

To make a script executable directly from the shell, using the guix executable that is on the user's search path, add the following two lines at the top of the script:

     #!/usr/bin/env -S guix repl --
     !#

To make a script that launches an interactive REPL directly from the shell, use the --interactive flag:

     #!/usr/bin/env -S guix repl --interactive
     !#

Without a file name argument, a Guile REPL is started, allowing for interactive use (see Using Guix Interactively):

     $ guix repl
     scheme@(guile-user)> ,use (gnu packages base)
     scheme@(guile-user)> coreutils
     $1 = #<package coreutils@8.29 gnu/packages/base.scm:327 3e28300>

In addition, guix repl implements a simple machine-readable REPL protocol for use by (guix inferior), a facility to interact with inferiors, separate processes running a potentially different revision of Guix.

The available options are as follows:

--list-types
     Display the TYPE options for guix repl --type=TYPE and exit.

--type=TYPE
-t TYPE
     Start a REPL of the given TYPE, which can be one of the following:

     guile
          This is default, and it spawns a standard full-featured Guile REPL.

     machine
          Spawn a REPL that uses the machine-readable protocol.  This is the protocol that the (guix inferior) module speaks.

--listen=ENDPOINT
     By default, guix repl reads from standard input and writes to standard output.  When this option is passed, it will instead listen for connections on ENDPOINT.  Here are examples of valid options:

     --listen=tcp:37146
          Accept connections on localhost on port 37146.

     --listen=unix:/tmp/socket
          Accept connections on the Unix-domain socket /tmp/socket.

--interactive
-i
     Launch the interactive REPL after FILE is executed.

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

     This allows users to define their own packages and make them visible to the script or REPL.

-q
     Inhibit loading of the ~/.guile file.  By default, that configuration file is loaded when spawning a guile REPL.

Using Guix Interactively
========================

The guix repl command gives you access to a warm and friendly read-eval-print loop (REPL) (see Invoking guix repl).  If you're getting into Guix programming---defining your own packages, writing manifests, defining services for Guix System or Guix Home, etc.---you will surely find it convenient to toy with ideas at the REPL.

If you use Emacs, the most convenient way to do that is with Geiser (see The Perfect Setup), but you do not have to use Emacs to enjoy the REPL.  When using guix repl or guile in the terminal, we recommend using Readline for completion and Colorized to get colorful output.  To do that, you can run:

     guix install guile guile-readline guile-colorized

... and then create a .guile file in your home directory containing this:

     (use-modules (ice-9 readline) (ice-9 colorized))

     (activate-readline)
     (activate-colorized)

The REPL lets you evaluate Scheme code; you type a Scheme expression at the prompt, and the REPL prints what it evaluates to:

     $ guix repl
     scheme@(guix-user)> (+ 2 3)
     $1 = 5
     scheme@(guix-user)> (string-append "a" "b")
     $2 = "ab"

It becomes interesting when you start fiddling with Guix at the REPL. The first thing you'll want to do is to ``import'' the (guix) module, which gives access to the main part of the programming interface, and perhaps a bunch of useful Guix modules.  You could type (use-modules (guix)), which is valid Scheme code to import a module (see Using Guile Modules (GNU Guile Reference Manual)), but the REPL provides the use command as a shorthand notation (see REPL Commands (GNU Guile Reference Manual)):

     scheme@(guix-user)> ,use (guix)
     scheme@(guix-user)> ,use (gnu packages base)

Notice that REPL commands are introduced by a leading comma.  A REPL command like use is not valid Scheme code; it's interpreted specially by the REPL.

Guix extends the Guile REPL with additional commands for convenience. Among those, the build command comes in handy: it ensures that the given file-like object is built, building it if needed, and returns its output file name(s).  In the example below, we build the coreutils and grep packages, as well as a ``computed file'' (see computed-file), and we use the scandir procedure to list the files in Grep's /bin directory:

     scheme@(guix-user)> ,build coreutils
     $1 = "/gnu/store/...-coreutils-8.32-debug"
     $2 = "/gnu/store/...-coreutils-8.32"
     scheme@(guix-user)> ,build grep
     $3 = "/gnu/store/...-grep-3.6"
     scheme@(guix-user)> ,build (computed-file "x" #~(mkdir #$output))
     building /gnu/store/...-x.drv...
     $4 = "/gnu/store/...-x"
     scheme@(guix-user)> ,use(ice-9 ftw)
     scheme@(guix-user)> (scandir (string-append $3 "/bin"))
     $5 = ("." ".." "egrep" "fgrep" "grep")

As a packager, you may be willing to inspect the build phases or flags of a given package; this is particularly useful when relying a lot on inheritance to define package variants (see Defining Package Variants) or when package arguments are a result of some computation, both of which can make it harder to foresee what ends up in the package arguments.  Additional commands let you inspect those package arguments:

     scheme@(guix-user)> ,phases grep
     $1 = (modify-phases %standard-phases
            (add-after 'install 'fix-egrep-and-fgrep
              (lambda* (#:key outputs #:allow-other-keys)
                (let* ((out (assoc-ref outputs "out"))
                       (bin (string-append out "/bin")))
                  (substitute* (list (string-append bin "/egrep")
                                     (string-append bin "/fgrep"))
                    (("^exec grep")
                     (string-append "exec " bin "/grep")))))))
     scheme@(guix-user)> ,configure-flags findutils
     $2 = (list "--localstatedir=/var")
     scheme@(guix-user)> ,make-flags binutils
     $3 = '("MAKEINFO=true")

At a lower-level, a useful command is lower: it takes a file-like object and ``lowers'' it into a derivation (see Derivations) or a store file:

     scheme@(guix-user)> ,lower grep
     $6 = #<derivation /gnu/store/...-grep-3.6.drv => /gnu/store/...-grep-3.6 7f0e639115f0>
     scheme@(guix-user)> ,lower (plain-file "x" "Hello!")
     $7 = "/gnu/store/...-x"

The full list of REPL commands can be seen by typing ,help guix and is given below for reference.

 -- REPL command: build OBJECT
     Lower OBJECT and build it if it's not already built, returning its output file name(s).

 -- REPL command: lower OBJECT
     Lower OBJECT into a derivation or store file name and return it.

 -- REPL command: verbosity LEVEL
     Change build verbosity to LEVEL.

     This is similar to the --verbosity command-line option (see Common Build Options): level 0 means total silence, level 1 shows build events only, and higher levels print build logs.

 -- REPL command: phases PACKAGE
 -- REPL command: configure-flags PACKAGE
 -- REPL command: make-flags PACKAGE
     These REPL commands return the value of one element of the arguments field of PACKAGE (see package Reference): the first one show the staged code associated with #:phases (see Build Phases), the second shows the code for #:configure-flags, and ,make-flags returns the code for #:make-flags.

 -- REPL command: run-in-store EXP
     Run EXP, a monadic expression, through the store monad. See The Store Monad, for more information.

 -- REPL command: enter-store-monad
     Enter a new REPL to evaluate monadic expressions (see The Store Monad).  You can quit this ``inner'' REPL by typing ,q.

Utilities
*********

This section describes Guix command-line utilities.  Some of them are primarily targeted at developers and users who write new package definitions, while others are more generally useful.  They complement the Scheme programming interface of Guix in a convenient way.

Invoking guix build
===================

The guix build command builds packages or derivations and their dependencies, and prints the resulting store paths.  Note that it does not modify the user's profile---this is the job of the guix package command (see Invoking guix package).  Thus, it is mainly useful for distribution developers.

The general syntax is:

     guix build OPTIONS PACKAGE-OR-DERIVATION...

As an example, the following command builds the latest versions of Emacs and of Guile, displays their build logs, and finally displays the resulting directories:

     guix build emacs guile

Similarly, the following command builds all the available packages:

     guix build --quiet --keep-going \
       $(guix package -A | awk '{ print $1 "@" $2 }')

PACKAGE-OR-DERIVATION may be either the name of a package found in the software distribution such as coreutils or coreutils@8.20, or a derivation such as /gnu/store/...-coreutils-8.19.drv.  In the former case, a package with the corresponding name (and optionally version) is searched for among the GNU distribution modules (see Package Modules).

Alternatively, the --expression option may be used to specify a Scheme expression that evaluates to a package; this is useful when disambiguating among several same-named packages or package variants is needed.

There may be zero or more OPTIONS.  The available options are described in the subsections below.

Common Build Options
--------------------

A number of options that control the build process are common to guix build and other commands that can spawn builds, such as guix package or guix archive.  These are the following:

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

     This allows users to define their own packages and make them visible to the command-line tools.

--keep-failed
-K
     Keep the build tree of failed builds.  Thus, if a build fails, its build tree is kept under /tmp, in a directory whose name is shown at the end of the build log.  This is useful when debugging build issues. See Debugging Build Failures, for tips and tricks on how to debug build issues.

     This option implies --no-offload, and it has no effect when connecting to a remote daemon with a guix:// URI (see the GUIX_DAEMON_SOCKET variable).

--keep-going
-k
     Keep going when some of the derivations fail to build; return only once all the builds have either completed or failed.

     The default behavior is to stop as soon as one of the specified derivations has failed.

--dry-run
-n
     Do not build the derivations.

--fallback
     When substituting a pre-built binary fails, fall back to building packages locally (see Substitution Failure).

--substitute-urls=URLS
     Consider URLS the whitespace-separated list of substitute source URLs, overriding the default list of URLs of guix-daemon (see guix-daemon URLs).

     This means that substitutes may be downloaded from URLS, provided they are signed by a key authorized by the system administrator (see Substitutes).

     When URLS is the empty string, substitutes are effectively disabled.

--no-substitutes
     Do not use substitutes for build products.  That is, always build things locally instead of allowing downloads of pre-built binaries (see Substitutes).

--no-grafts
     Do not ``graft'' packages.  In practice, this means that package updates available as grafts are not applied.  See Security Updates, for more information on grafts.

--rounds=N
     Build each derivation N times in a row, and raise an error if consecutive build results are not bit-for-bit identical.

     This is a useful way to detect non-deterministic builds processes. Non-deterministic build processes are a problem because they make it practically impossible for users to verify whether third-party binaries are genuine.  See Invoking guix challenge, for more.

     When used in conjunction with --keep-failed, the differing output is kept in the store, under /gnu/store/...-check. This makes it easy to look for differences between the two results.

--no-offload
     Do not use offload builds to other machines (see Daemon Offload Setup).  That is, always build things locally instead of offloading builds to remote machines.

--max-silent-time=SECONDS
     When the build or substitution process remains silent for more than SECONDS, terminate it and report a build failure.

     By default, the daemon's setting is honored (see --max-silent-time).

--timeout=SECONDS
     Likewise, when the build or substitution process lasts for more than SECONDS, terminate it and report a build failure.

     By default, the daemon's setting is honored (see --timeout).

-v LEVEL
--verbosity=LEVEL
     Use the given verbosity LEVEL, an integer.  Choosing 0 means that no output is produced, 1 is for quiet output; 2 is similar to 1 but it additionally displays download URLs; 3 shows all the build log output on standard error.

--cores=N
-c N
     Allow the use of up to N CPU cores for the build.  The special value 0 means to use as many CPU cores as available.

--max-jobs=N
-M N
     Allow at most N build jobs in parallel.  See --max-jobs, for details about this option and the equivalent guix-daemon option.

--debug=LEVEL
     Produce debugging output coming from the build daemon.  LEVEL must be an integer between 0 and 5; higher means more verbose output.  Setting a level of 4 or more may be helpful when debugging setup issues with the build daemon.

Behind the scenes, guix build is essentially an interface to the package-derivation procedure of the (guix packages) module, and to the build-derivations procedure of the (guix derivations) module.

In addition to options explicitly passed on the command line, guix build and other guix commands that support building honor the GUIX_BUILD_OPTIONS environment variable.

 -- Environment Variable: GUIX_BUILD_OPTIONS
     Users can define this variable to a list of command line options that will automatically be used by guix build and other guix commands that can perform builds, as in the example below:

          $ export GUIX_BUILD_OPTIONS="--no-substitutes -c 2 -L /foo/bar"

     These options are parsed independently, and the result is appended to the parsed command-line options.

Package Transformation Options
------------------------------

Another set of command-line options supported by guix build and also guix package are package transformation options.  These are options that make it possible to define package variants---for instance, packages built from different source code. This is a convenient way to create customized packages on the fly without having to type in the definitions of package variants (see Defining Packages).

Package transformation options are preserved across upgrades: guix upgrade attempts to apply transformation options initially used when creating the profile to the upgraded packages.

The available options are listed below.  Most commands support them and also support a --help-transform option that lists all the available options and a synopsis (these options are not shown in the --help output for brevity).

--tune[=CPU]
     Use versions of the packages marked as ``tunable'' optimized for CPU.  When CPU is native, or when it is omitted, tune for the CPU on which the guix command is running.

     Valid CPU names are those recognized by the underlying compiler, by default the GNU Compiler Collection.  On x86_64 processors, this includes CPU names such as nehalem, haswell, and skylake (see -march (Using the GNU Compiler Collection (GCC))).

     As new generations of CPUs come out, they augment the standard instruction set architecture (ISA) with additional instructions, in particular instructions for single-instruction/multiple-data (SIMD) parallel processing.  For example, while Core2 and Skylake CPUs both implement the x86_64 ISA, only the latter supports AVX2 SIMD instructions.

     The primary gain one can expect from --tune is for programs that can make use of those SIMD capabilities and that do not already have a mechanism to select the right optimized code at run time. Packages that have the tunable? property set are considered tunable packages by the --tune option; a package definition with the property set looks like this:

          (package
            (name "hello-simd")
            ;; ...

            ;; This package may benefit from SIMD extensions so
            ;; mark it as "tunable".
            (properties '((tunable? . #t))))

     Other packages are not considered tunable.  This allows Guix to use generic binaries in the cases where tuning for a specific CPU is unlikely to provide any gain.

     Tuned packages are built with -march=CPU; under the hood, the -march option is passed to the actual wrapper by a compiler wrapper.  Since the build machine may not be able to run code for the target CPU micro-architecture, the test suite is not run when building a tuned package.

     To reduce rebuilds to the minimum, tuned packages are grafted onto packages that depend on them (see grafts). Thus, using --no-grafts cancels the effect of --tune.

     We call this technique package multi-versioning: several variants of tunable packages may be built, one for each CPU variant.  It is the coarse-grain counterpart of function multi-versioning as implemented by the GNU tool chain (see Function Multiversioning (Using the GNU Compiler Collection (GCC))).

--with-source=SOURCE
--with-source=PACKAGE=SOURCE
--with-source=PACKAGE@VERSION=SOURCE
     Use SOURCE as the source of PACKAGE, and VERSION as its version number. SOURCE must be a file name or a URL, as for guix download (see Invoking guix download).

     When PACKAGE is omitted, it is taken to be the package name specified on the command line that matches the base of SOURCE---e.g., if SOURCE is /src/guile-2.0.10.tar.gz, the corresponding package is guile.

     Likewise, when VERSION is omitted, the version string is inferred from SOURCE; in the previous example, it is 2.0.10.

     This option allows users to try out versions of packages other than the one provided by the distribution.  The example below downloads ed-1.7.tar.gz from a GNU mirror and uses that as the source for the ed package:

          guix build ed --with-source=mirror://gnu/ed/ed-1.4.tar.gz

     As a developer, --with-source makes it easy to test release candidates, and even to test their impact on packages that depend on them:

          guix build elogind --with-source=.../shepherd-0.9.0rc1.tar.gz

     ... or to build from a checkout in a pristine environment:

          $ git clone git://git.sv.gnu.org/guix.git
          $ guix build guix --with-source=guix@1.0=./guix

--with-input=PACKAGE=REPLACEMENT
     Replace dependency on PACKAGE by a dependency on REPLACEMENT.  PACKAGE must be a package name, and REPLACEMENT must be a package specification such as guile or guile@1.8.

     For instance, the following command builds Guix, but replaces its dependency on the current stable version of Guile with a dependency on the legacy version of Guile, guile@2.2:

          guix build --with-input=guile=guile@2.2 guix

     This is a recursive, deep replacement.  So in this example, both guix and its dependency guile-json (which also depends on guile) get rebuilt against guile@2.2.

     This is implemented using the package-input-rewriting/spec Scheme procedure (see package-input-rewriting/spec).

--with-graft=PACKAGE=REPLACEMENT
     This is similar to --with-input but with an important difference: instead of rebuilding the whole dependency chain, REPLACEMENT is built and then grafted onto the binaries that were initially referring to PACKAGE.  See Security Updates, for more information on grafts.

     For example, the command below grafts version 3.5.4 of GnuTLS onto Wget and all its dependencies, replacing references to the version of GnuTLS they currently refer to:

          guix build --with-graft=gnutls=gnutls@3.5.4 wget

     This has the advantage of being much faster than rebuilding everything. But there is a caveat: it works if and only if PACKAGE and REPLACEMENT are strictly compatible---for example, if they provide a library, the application binary interface (ABI) of those libraries must be compatible.  If REPLACEMENT is somehow incompatible with PACKAGE, then the resulting package may be unusable.  Use with care!

--with-debug-info=PACKAGE
     Build PACKAGE in a way that preserves its debugging info and graft it onto packages that depend on it.  This is useful if PACKAGE does not already provide debugging info as a debug output (see Installing Debugging Files).

     For example, suppose you're experiencing a crash in Inkscape and would like to see what's up in GLib, a library deep down in Inkscape's dependency graph.  GLib lacks a debug output, so debugging is tough.  Fortunately, you rebuild GLib with debugging info and tack it on Inkscape:

          guix install inkscape --with-debug-info=glib

     Only GLib needs to be recompiled so this takes a reasonable amount of time.  See Installing Debugging Files, for more info.

          Under the hood, this option works by passing the #:strip-binaries? #f to the build system of the package of interest (see Build Systems).  Most build systems support that option but some do not.  In that case, an error is raised.

          Likewise, if a C/C++ package is built without -g (which is rarely the case), debugging info will remain unavailable even when #:strip-binaries? is false.

--with-c-toolchain=PACKAGE=TOOLCHAIN
     This option changes the compilation of PACKAGE and everything that depends on it so that they get built with TOOLCHAIN instead of the default GNU tool chain for C/C++.

     Consider this example:

          guix build octave-cli \
            --with-c-toolchain=fftw=gcc-toolchain@10 \
            --with-c-toolchain=fftwf=gcc-toolchain@10

     The command above builds a variant of the fftw and fftwf packages using version 10 of gcc-toolchain instead of the default tool chain, and then builds a variant of the GNU Octave command-line interface using them.  GNU Octave itself is also built with gcc-toolchain@10.

     This other example builds the Hardware Locality (hwloc) library and its dependents up to intel-mpi-benchmarks with the Clang C compiler:

          guix build --with-c-toolchain=hwloc=clang-toolchain \
                     intel-mpi-benchmarks

          There can be application binary interface (ABI) incompatibilities among tool chains.  This is particularly true of the C++ standard library and run-time support libraries such as that of OpenMP.  By rebuilding all dependents with the same tool chain, --with-c-toolchain minimizes the risks of incompatibility but cannot entirely eliminate them.  Choose PACKAGE wisely.

--with-git-url=PACKAGE=URL
     Build PACKAGE from the latest commit of the master branch of the Git repository at URL.  Git sub-modules of the repository are fetched, recursively.

     For example, the following command builds the NumPy Python library against the latest commit of the master branch of Python itself:

          guix build python-numpy \
            --with-git-url=python=https://github.com/python/cpython

     This option can also be combined with --with-branch or --with-commit (see below).

     Obviously, since it uses the latest commit of the given branch, the result of such a command varies over time.  Nevertheless it is a convenient way to rebuild entire software stacks against the latest commit of one or more packages.  This is particularly useful in the context of continuous integration (CI).

     Checkouts are kept in a cache under ~/.cache/guix/checkouts to speed up consecutive accesses to the same repository.  You may want to clean it up once in a while to save disk space.

--with-branch=PACKAGE=BRANCH
     Build PACKAGE from the latest commit of BRANCH.  If the source field of PACKAGE is an origin with the git-fetch method (see origin Reference) or a git-checkout object, the repository URL is taken from that source.  Otherwise you have to use --with-git-url to specify the URL of the Git repository.

     For instance, the following command builds guile-sqlite3 from the latest commit of its master branch, and then builds guix (which depends on it) and cuirass (which depends on guix) against this specific guile-sqlite3 build:

          guix build --with-branch=guile-sqlite3=master cuirass

--with-commit=PACKAGE=COMMIT
     This is similar to --with-branch, except that it builds from COMMIT rather than the tip of a branch.  COMMIT must be a valid Git commit SHA1 identifier, a tag, or a git describe style identifier such as 1.0-3-gabc123.

--with-patch=PACKAGE=FILE
     Add FILE to the list of patches applied to PACKAGE, where PACKAGE is a spec such as python@3.8 or glibc. FILE must contain a patch; it is applied with the flags specified in the origin of PACKAGE (see origin Reference), which by default includes -p1 (see patch Directories (Comparing and Merging Files)).

     As an example, the command below rebuilds Coreutils with the GNU C Library (glibc) patched with the given patch:

          guix build coreutils --with-patch=glibc=./glibc-frob.patch

     In this example, glibc itself as well as everything that leads to Coreutils in the dependency graph is rebuilt.

--with-configure-flag=PACKAGE=FLAG
     Append FLAG to the configure flags of PACKAGE, where PACKAGE is a spec such as guile@3.0 or glibc.  The build system of PACKAGE must support the #:configure-flags argument.

     For example, the command below builds GNU Hello with the configure flag --disable-nls:

          guix build hello --with-configure-flag=hello=--disable-nls

     The following command passes an extra flag to cmake as it builds lapack:

          guix build lapack \
            --with-configure-flag=lapack=-DBUILD_SHARED_LIBS=OFF

          Under the hood, this option works by passing the #:configure-flags argument to the build system of the package of interest (see Build Systems).  Most build systems support that option but some do not.  In that case, an error is raised.

--with-latest=PACKAGE
--with-version=PACKAGE=VERSION
     So you like living on the bleeding edge?  The --with-latest option is for you!  It replaces occurrences of PACKAGE in the dependency graph with its latest upstream version, as reported by guix refresh (see Invoking guix refresh).

     It does so by determining the latest upstream release of PACKAGE (if possible), downloading it, and authenticating it if it comes with an OpenPGP signature.

     As an example, the command below builds Guix against the latest version of Guile-JSON:

          guix build guix --with-latest=guile-json

     The --with-version works similarly except that it lets you specify that you want precisely VERSION, assuming that version exists upstream.  For example, to spawn a development environment with SciPy built against version 1.22.4 of NumPy (skipping its test suite because hey, we're not gonna wait this long), you would run:

          guix shell python python-scipy --with-version=python-numpy=1.22.4

          Because they depend on source code published at a given point in time on upstream servers, deployments made with --with-latest and --with-version may be non-reproducible: source might disappear or be modified in place on the servers.

          To deploy old software versions without compromising on reproducibility, see guix time-machine.

     There are limitations.  First, in cases where the tool cannot or does not know how to authenticate source code, you are at risk of running malicious code; a warning is emitted in this case.  Second, this option simply changes the source used in the existing package definitions, which is not always sufficient: there might be additional dependencies that need to be added, patches to apply, and more generally the quality assurance work that Guix developers normally do will be missing.

     You've been warned!  When those limitations are acceptable, it's a snappy way to stay on top.  We encourage you to submit patches updating the actual package definitions once you have successfully tested an upgrade with --with-latest (see Contributing).

--without-tests=PACKAGE
     Build PACKAGE without running its tests.  This can be useful in situations where you want to skip the lengthy test suite of a intermediate package, or if a package's test suite fails in a non-deterministic fashion.  It should be used with care because running the test suite is a good way to ensure a package is working as intended.

     Turning off tests leads to a different store item.  Consequently, when using this option, anything that depends on PACKAGE must be rebuilt, as in this example:

          guix install --without-tests=python python-notebook

     The command above installs python-notebook on top of python built without running its test suite.  To do so, it also rebuilds everything that depends on python, including python-notebook itself.

     Internally, --without-tests relies on changing the #:tests? option of a package's check phase (see Build Systems).  Note that some packages use a customized check phase that does not respect a #:tests? #f setting.  Therefore, --without-tests has no effect on these packages.

Wondering how to achieve the same effect using Scheme code, for example in your manifest, or how to write your own package transformation? See Defining Package Variants, for an overview of the programming interfaces available.

Additional Build Options
------------------------

The command-line options presented below are specific to guix build.

--quiet
-q
     Build quietly, without displaying the build log; this is equivalent to --verbosity=0.  Upon completion, the build log is kept in /var (or similar) and can always be retrieved using the --log-file option.

--file=FILE
-f FILE
     Build the package, derivation, or other file-like object that the code within FILE evaluates to (see file-like objects).

     As an example, FILE might contain a package definition like this (see Defining Packages):

               [file package-hello.scm not included]

     The FILE may also contain a JSON representation of one or more package definitions.  Running guix build -f on hello.json with the following contents would result in building the packages myhello and greeter:

               [file package-hello.json not included]

--manifest=MANIFEST
-m MANIFEST
     Build all packages listed in the given MANIFEST (see --manifest).

--expression=EXPR
-e EXPR
     Build the package or derivation EXPR evaluates to.

     For example, EXPR may be (@ (gnu packages guile) guile-1.8), which unambiguously designates this specific variant of version 1.8 of Guile.

     Alternatively, EXPR may be a G-expression, in which case it is used as a build program passed to gexp->derivation (see G-Expressions).

     Lastly, EXPR may refer to a zero-argument monadic procedure (see The Store Monad).  The procedure must return a derivation as a monadic value, which is then passed through run-with-store.

--source
-S
     Build the source derivations of the packages, rather than the packages themselves.

     For instance, guix build -S gcc returns something like /gnu/store/...-gcc-4.7.2.tar.bz2, which is the GCC source tarball.

     The returned source tarball is the result of applying any patches and code snippets specified in the package origin (see Defining Packages).

     As with other derivations, the result of building a source derivation can be verified using the --check option (see build-check). This is useful to validate that a (potentially already built or substituted, thus cached) package source matches against its declared hash.

     Note that guix build -S compiles the sources only of the specified packages.  They do not include the sources of statically linked dependencies and by themselves are insufficient for reproducing the packages.

--sources
     Fetch and return the source of PACKAGE-OR-DERIVATION and all their dependencies, recursively.  This is a handy way to obtain a local copy of all the source code needed to build PACKAGES, allowing you to eventually build them even without network access.  It is an extension of the --source option and can accept one of the following optional argument values:

     package
          This value causes the --sources option to behave in the same way as the --source option.

     all
          Build the source derivations of all packages, including any source that might be listed as inputs.  This is the default value.

               $ guix build --sources tzdata
               The following derivations will be built:
                  /gnu/store/...-tzdata2015b.tar.gz.drv
                  /gnu/store/...-tzcode2015b.tar.gz.drv

     transitive
          Build the source derivations of all packages, as well of all transitive inputs to the packages.  This can be used e.g. to prefetch package source for later offline building.

               $ guix build --sources=transitive tzdata
               The following derivations will be built:
                  /gnu/store/...-tzcode2015b.tar.gz.drv
                  /gnu/store/...-findutils-4.4.2.tar.xz.drv
                  /gnu/store/...-grep-2.21.tar.xz.drv
                  /gnu/store/...-coreutils-8.23.tar.xz.drv
                  /gnu/store/...-make-4.1.tar.xz.drv
                  /gnu/store/...-bash-4.3.tar.xz.drv
               ...

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM---e.g., i686-linux---instead of the system type of the build host.  The guix build command allows you to repeat this option several times, in which case it builds for all the specified systems; other commands ignore extraneous -s options.

          The --system flag is for native compilation and must not be confused with cross-compilation.  See --target below for information on cross-compilation.

     An example use of this is on Linux-based systems, which can emulate different personalities.  For instance, passing --system=i686-linux on an x86_64-linux system or --system=armhf-linux on an aarch64-linux system allows you to build packages in a complete 32-bit environment.

          Building for an armhf-linux system is unconditionally enabled on aarch64-linux machines, although certain aarch64 chipsets do not allow for this functionality, notably the ThunderX.

     Similarly, when transparent emulation with QEMU and binfmt_misc is enabled (see qemu-binfmt-service-type), you can build for any system for which a QEMU binfmt_misc handler is installed.

     Builds for a system other than that of the machine you are using can also be offloaded to a remote machine of the right architecture. See Daemon Offload Setup, for more information on offloading.

--target=TRIPLET
     Cross-build for TRIPLET, which must be a valid GNU triplet, such as "aarch64-linux-gnu" (see GNU configuration triplets (Autoconf)).

--list-systems
     List all the supported systems, that can be passed as an argument to --system.

--list-targets
     List all the supported targets, that can be passed as an argument to --target.

--check
     Rebuild PACKAGE-OR-DERIVATION, which are already available in the store, and raise an error if the build results are not bit-for-bit identical.

     This mechanism allows you to check whether previously installed substitutes are genuine (see Substitutes), or whether the build result of a package is deterministic.  See Invoking guix challenge, for more background information and tools.

     When used in conjunction with --keep-failed, the differing output is kept in the store, under /gnu/store/...-check. This makes it easy to look for differences between the two results.

--repair
     Attempt to repair the specified store items, if they are corrupt, by re-downloading or rebuilding them.

     This operation is not atomic and thus restricted to root.

--derivations
-d
     Return the derivation paths, not the output paths, of the given packages.

--root=FILE
-r FILE
     Make FILE a symlink to the result, and register it as a garbage collector root.

     Consequently, the results of this guix build invocation are protected from garbage collection until FILE is removed.  When that option is omitted, build results are eligible for garbage collection as soon as the build completes.  See Invoking guix gc, for more on GC roots.

--log-file
     Return the build log file names or URLs for the given PACKAGE-OR-DERIVATION, or raise an error if build logs are missing.

     This works regardless of how packages or derivations are specified.  For instance, the following invocations are equivalent:

          guix build --log-file $(guix build -d guile)
          guix build --log-file $(guix build guile)
          guix build --log-file guile
          guix build --log-file -e '(@ (gnu packages guile) guile-2.0)'

     If a log is unavailable locally, and unless --no-substitutes is passed, the command looks for a corresponding log on one of the substitute servers (as specified with --substitute-urls).

     So for instance, imagine you want to see the build log of GDB on aarch64, but you are actually on an x86_64 machine:

          $ guix build --log-file gdb -s aarch64-linux
          https://ci.guix.gnu.org/log/...-gdb-7.10

     You can freely access a huge library of build logs!

Debugging Build Failures
------------------------

When defining a new package (see Defining Packages), you will probably find yourself spending some time debugging and tweaking the build until it succeeds.  To do that, you need to operate the build commands yourself in an environment as close as possible to the one the build daemon uses.

To that end, the first thing to do is to use the --keep-failed or -K option of guix build, which will keep the failed build tree in /tmp or whatever directory you specified as TMPDIR (see --keep-failed).

From there on, you can cd to the failed build tree and source the environment-variables file, which contains all the environment variable definitions that were in place when the build failed.  So let's say you're debugging a build failure in package foo; a typical session would look like this:

     $ guix build foo -K
     ... build fails
     $ cd /tmp/guix-build-foo.drv-0
     $ source ./environment-variables
     $ cd foo-1.2

Now, you can invoke commands as if you were the daemon (almost) and troubleshoot your build process.

Sometimes it happens that, for example, a package's tests pass when you run them manually but they fail when the daemon runs them.  This can happen because the daemon runs builds in containers where, unlike in our environment above, network access is missing, /bin/sh does not exist, etc. (see Build Environment Setup).

In such cases, you may need to inspect the build process from within a container similar to the one the build daemon creates:

     $ guix build -K foo
     ...
     $ cd /tmp/guix-build-foo.drv-0
     $ guix shell --no-grafts -C -D foo strace gdb
     [env]# source ./environment-variables
     [env]# cd foo-1.2

Here, guix shell -C creates a container and spawns a new shell in it (see Invoking guix shell).  The strace gdb part adds the strace and gdb commands to the container, which you may find handy while debugging.  The --no-grafts option makes sure we get the exact same environment, with ungrafted packages (see Security Updates, for more info on grafts).

To get closer to a container like that used by the build daemon, we can remove /bin/sh:

     [env]# rm /bin/sh

(Don't worry, this is harmless: this is all happening in the throw-away container created by guix shell.)

The strace command is probably not in the search path, but we can run:

     [env]# $GUIX_ENVIRONMENT/bin/strace -f -o log make check

In this way, not only you will have reproduced the environment variables the daemon uses, you will also be running the build process in a container similar to the one the daemon uses.

Invoking guix edit
==================

So many packages, so many source files!  The guix edit command facilitates the life of users and packagers by pointing their editor at the source file containing the definition of the specified packages. For instance:

     guix edit gcc@4.9 vim

launches the program specified in the VISUAL or in the EDITOR environment variable to view the recipe of GCC 4.9.3 and that of Vim.

If you are using a Guix Git checkout (see Building from Git), or have created your own packages on GUIX_PACKAGE_PATH (see Package Modules), you will be able to edit the package recipes.  In other cases, you will be able to examine the read-only recipes for packages currently in the store.

Instead of GUIX_PACKAGE_PATH, the command-line option --load-path=DIRECTORY (or in short -L DIRECTORY) allows you to add DIRECTORY to the front of the package module search path and so make your own packages visible.

Invoking guix download
======================

When writing a package definition, developers typically need to download a source tarball, compute its SHA256 hash, and write that hash in the package definition (see Defining Packages).  The guix download tool helps with this task: it downloads a file from the given URI, adds it to the store, and prints both its file name in the store and its SHA256 hash.

The fact that the downloaded file is added to the store saves bandwidth: when the developer eventually tries to build the newly defined package with guix build, the source tarball will not have to be downloaded again because it is already in the store.  It is also a convenient way to temporarily stash files, which may be deleted eventually (see Invoking guix gc).

The guix download command supports the same URIs as used in package definitions.  In particular, it supports mirror:// URIs. https URIs (HTTP over TLS) are supported provided the Guile bindings for GnuTLS are available in the user's environment; when they are not available, an error is raised.  See how to install the GnuTLS bindings for Guile (GnuTLS-Guile), for more information.

guix download verifies HTTPS server certificates by loading the certificates of X.509 authorities from the directory pointed to by the SSL_CERT_DIR environment variable (see X.509 Certificates), unless --no-check-certificate is used.

Alternatively, guix download can also retrieve a Git repository, possibly a specific commit, tag, or branch.

The following options are available:

--hash=ALGORITHM
-H ALGORITHM
     Compute a hash using the specified ALGORITHM.  See Invoking guix hash, for more information.

--format=FMT
-f FMT
     Write the hash in the format specified by FMT.  For more information on the valid values for FMT, see Invoking guix hash.

--no-check-certificate
     Do not validate the X.509 certificates of HTTPS servers.

     When using this option, you have absolutely no guarantee that you are communicating with the authentic server responsible for the given URL, which makes you vulnerable to ``man-in-the-middle'' attacks.

--output=FILE
-o FILE
     Save the downloaded file to FILE instead of adding it to the store.

--git
-g
     Checkout the Git repository at the latest commit on the default branch.

--commit=COMMIT-OR-TAG
     Checkout the Git repository at COMMIT-OR-TAG.

     COMMIT-OR-TAG can be either a tag or a commit defined in the Git repository.

--branch=BRANCH
     Checkout the Git repository at BRANCH.

     The repository will be checked out at the latest commit of BRANCH, which must be a valid branch of the Git repository.

--recursive
-r
     Recursively clone the Git repository.

Invoking guix hash
==================

The guix hash command computes the hash of a file. It is primarily a convenience tool for anyone contributing to the distribution: it computes the cryptographic hash of one or more files, which can be used in the definition of a package (see Defining Packages).

The general syntax is:

     guix hash OPTION FILE ...

When FILE is - (a hyphen), guix hash computes the hash of data read from standard input.  guix hash has the following options:

--hash=ALGORITHM
-H ALGORITHM
     Compute a hash using the specified ALGORITHM, sha256 by default.

     ALGORITHM must be the name of a cryptographic hash algorithm supported by Libgcrypt via Guile-Gcrypt---e.g., sha512 or sha3-256 (see Hash Functions (Guile-Gcrypt Reference Manual)).

--format=FMT
-f FMT
     Write the hash in the format specified by FMT.

     Supported formats: base64, nix-base32, base32, base16 (hex and hexadecimal can be used as well).

     If the --format option is not specified, guix hash will output the hash in nix-base32.  This representation is used in the definitions of packages.

--recursive
-r
     The --recursive option is deprecated in favor of --serializer=nar (see below); -r remains accepted as a convenient shorthand.

--serializer=TYPE
-S TYPE
     Compute the hash on FILE using TYPE serialization.

     TYPE may be one of the following:

     none
          This is the default: it computes the hash of a file's contents.

     nar
          Compute the hash of a ``normalized archive'' (or ``nar'') containing FILE, including its children if it is a directory.  Some of the metadata of FILE is part of the archive; for instance, when FILE is a regular file, the hash is different depending on whether FILE is executable or not.  Metadata such as time stamps have no impact on the hash (see Invoking guix archive, for more info on the nar format).

     git
          Compute the hash of the file or directory as a Git ``tree'', following the same method as the Git version control system.

--exclude-vcs
-x
     When combined with --recursive, exclude version control system directories (.bzr, .git, .hg, etc.).

     As an example, here is how you would compute the hash of a Git checkout, which is useful when using the git-fetch method (see origin Reference):

          $ git clone http://example.org/foo.git
          $ cd foo
          $ guix hash -x --serializer=nar .

Invoking guix import
====================

The guix import command is useful for people who would like to add a package to the distribution with as little work as possible---a legitimate demand.  The command knows of a few repositories from which it can ``import'' package metadata.  The result is a package definition, or a template thereof, in the format we know (see Defining Packages).

The general syntax is:

     guix import IMPORTER OPTIONS...

IMPORTER specifies the source from which to import package metadata, and OPTIONS specifies a package identifier and other options specific to IMPORTER.

Some of the importers rely on the ability to run the gpgv command. For these, GnuPG must be installed and in $PATH; run guix install gnupg if needed.

Currently, the available ``importers'' are:

gnu
     Import metadata for the given GNU package.  This provides a template for the latest version of that GNU package, including the hash of its source tarball, and its canonical synopsis and description.

     Additional information such as the package dependencies and its license needs to be figured out manually.

     For example, the following command returns a package definition for GNU Hello:

          guix import gnu hello

     Specific command-line options are:

     --key-download=POLICY
          As for guix refresh, specify the policy to handle missing OpenPGP keys when verifying the package signature.  See --key-download.

pypi
     Import metadata from the Python Package Index (https://pypi.python.org/).  Information is taken from the JSON-formatted description available at pypi.python.org and usually includes all the relevant information, including package dependencies.  For maximum efficiency, it is recommended to install the unzip utility, so that the importer can unzip Python wheels and gather data from them.

     The command below imports metadata for the latest version of the itsdangerous Python package:

          guix import pypi itsdangerous

     You can also ask for a specific version:

          guix import pypi itsdangerous@1.1.0

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

gem
     Import metadata from RubyGems (https://rubygems.org/).  Information is taken from the JSON-formatted description available at rubygems.org and includes most relevant information, including runtime dependencies.  There are some caveats, however.  The metadata doesn't distinguish between synopses and descriptions, so the same string is used for both fields.  Additionally, the details of non-Ruby dependencies required to build native extensions is unavailable and left as an exercise to the packager.

     The command below imports metadata for the rails Ruby package:

          guix import gem rails

     You can also ask for a specific version:

          guix import gem rails@7.0.4

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

minetest
     Import metadata from ContentDB (https://content.minetest.net). Information is taken from the JSON-formatted metadata provided through ContentDB's API (https://content.minetest.net/help/api/) and includes most relevant information, including dependencies.  There are some caveats, however.  The license information is often incomplete. The commit hash is sometimes missing.  The descriptions are in the Markdown format, but Guix uses Texinfo instead.  Texture packs and subgames are unsupported.

     The command below imports metadata for the Mesecons mod by Jeija:

          guix import minetest Jeija/mesecons

     The author name can also be left out:

          guix import minetest mesecons

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

cpan
     Import metadata from MetaCPAN (https://www.metacpan.org/). Information is taken from the JSON-formatted metadata provided through MetaCPAN's API (https://fastapi.metacpan.org/) and includes most relevant information, such as module dependencies.  License information should be checked closely.  If Perl is available in the store, then the corelist utility will be used to filter core modules out of the list of dependencies.

     The command below imports metadata for the Acme::Boolean Perl module:

          guix import cpan Acme::Boolean

cran
     Import metadata from CRAN (https://cran.r-project.org/), the central repository for the GNU R statistical and graphical environment (https://r-project.org).

     Information is extracted from the DESCRIPTION file of the package.

     The command command below imports metadata for the Cairo R package:

          guix import cran Cairo

     You can also ask for a specific version:

          guix import cran rasterVis@0.50.3

     When --recursive is added, the importer will traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

     When --style=specification is added, the importer will generate package definitions whose inputs are package specifications instead of references to package variables.  This is useful when generated package definitions are to be appended to existing user modules, as the list of used package modules need not be changed.  The default is --style=variable.

     When --prefix=license: is added, the importer will prefix license atoms with license:, allowing a prefixed import of (guix licenses).

     When --archive=bioconductor is added, metadata is imported from Bioconductor (https://www.bioconductor.org/), a repository of R packages for the analysis and comprehension of high-throughput genomic data in bioinformatics.

     Information is extracted from the DESCRIPTION file contained in the package archive.

     The command below imports metadata for the GenomicRanges R package:

          guix import cran --archive=bioconductor GenomicRanges

     Finally, you can also import R packages that have not yet been published on CRAN or Bioconductor as long as they are in a git repository.  Use --archive=git followed by the URL of the git repository:

          guix import cran --archive=git https://github.com/immunogenomics/harmony

texlive
     Import TeX package information from the TeX Live package database for TeX packages that are part of the TeX Live distribution (https://www.tug.org/texlive/).

     Information about the package is obtained from the TeX Live package database, a plain text file that is included in the texlive-scripts package.  The source code is downloaded from possibly multiple locations in the SVN repository of the Tex Live project.

     The command command below imports metadata for the fontspec TeX package:

          guix import texlive fontspec

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

json
     Import package metadata from a local JSON file.  Consider the following example package definition in JSON format:

          {
            "name": "hello",
            "version": "2.10",
            "source": "mirror://gnu/hello/hello-2.10.tar.gz",
            "build-system": "gnu",
            "home-page": "https://www.gnu.org/software/hello/",
            "synopsis": "Hello, GNU world: An example GNU package",
            "description": "GNU Hello prints a greeting.",
            "license": "GPL-3.0+",
            "native-inputs": ["gettext"]
          }

     The field names are the same as for the <package> record (see Defining Packages).  References to other packages are provided as JSON lists of quoted package specification strings such as guile or guile@2.0.

     The importer also supports a more explicit source definition using the common fields for <origin> records:

          {
            ...
            "source": {
              "method": "url-fetch",
              "uri": "mirror://gnu/hello/hello-2.10.tar.gz",
              "sha256": {
                "base32": "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"
              }
            }
            ...
          }

     The command below reads metadata from the JSON file hello.json and outputs a package expression:

          guix import json hello.json

hackage
     Import metadata from the Haskell community's central package archive Hackage (https://hackage.haskell.org/).  Information is taken from Cabal files and includes all the relevant information, including package dependencies.

     Specific command-line options are:

     --stdin
     -s
          Read a Cabal file from standard input.

     --no-test-dependencies
     -t
          Do not include dependencies required only by the test suites.

     --cabal-environment=ALIST
     -e ALIST
          ALIST is a Scheme alist defining the environment in which the Cabal conditionals are evaluated.  The accepted keys are: os, arch, impl and a string representing the name of a flag. The value associated with a flag has to be either the symbol true or false.  The value associated with other keys has to conform to the Cabal file format definition.  The default value associated with the keys os, arch and impl is linux, x86_64 and ghc, respectively.

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

     The command below imports metadata for the latest version of the HTTP Haskell package without including test dependencies and specifying the value of the flag network-uri as false:

          guix import hackage -t -e "'((\"network-uri\" . false))" HTTP

     A specific package version may optionally be specified by following the package name by an at-sign and a version number as in the following example:

          guix import hackage mtl@2.1.3.1

stackage
     The stackage importer is a wrapper around the hackage one. It takes a package name, looks up the package version included in a long-term support (LTS) Stackage (https://www.stackage.org) release and uses the hackage importer to retrieve its metadata. Note that it is up to you to select an LTS release compatible with the GHC compiler used by Guix.

     Specific command-line options are:

     --no-test-dependencies
     -t
          Do not include dependencies required only by the test suites.

     --lts-version=VERSION
     -l VERSION
          VERSION is the desired LTS release version.  If omitted the latest release is used.

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

     The command below imports metadata for the HTTP Haskell package included in the LTS Stackage release version 7.18:

          guix import stackage --lts-version=7.18 HTTP

elpa
     Import metadata from an Emacs Lisp Package Archive (ELPA) package repository (see Packages (The GNU Emacs Manual)).

     Specific command-line options are:

     --archive=REPO
     -a REPO
          REPO identifies the archive repository from which to retrieve the information.  Currently the supported repositories and their identifiers are:

            - GNU (https://elpa.gnu.org/packages), selected by the gnu identifier.  This is the default.

               Packages from elpa.gnu.org are signed with one of the keys contained in the GnuPG keyring at share/emacs/25.1/etc/package-keyring.gpg (or similar) in the emacs package (see ELPA package signatures (The GNU Emacs Manual)).

            - NonGNU (https://elpa.nongnu.org/nongnu/), selected by the nongnu identifier.

            - MELPA-Stable (https://stable.melpa.org/packages), selected by the melpa-stable identifier.

            - MELPA (https://melpa.org/packages), selected by the melpa identifier.

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

crate
     Import metadata from the crates.io Rust package repository crates.io (https://crates.io), as in this example:

          guix import crate blake2-rfc

     The crate importer also allows you to specify a version string:

          guix import crate constant-time-eq@0.1.0

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

     --recursive-dev-dependencies
          If --recursive-dev-dependencies is specified, also the recursively imported packages contain their development dependencies, which are recursively imported as well.

     --allow-yanked
          If no non-yanked version of a crate is available, use the latest yanked version instead instead of aborting.

elm
     Import metadata from the Elm package repository package.elm-lang.org (https://package.elm-lang.org), as in this example:

          guix import elm elm-explorations/webgl

     The Elm importer also allows you to specify a version string:

          guix import elm elm-explorations/webgl@1.1.3

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

opam
     Import metadata from the OPAM (https://opam.ocaml.org/) package repository used by the OCaml community.

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

composer
     Import metadata from the Composer (https://getcomposer.org/) package archive used by the PHP community, as in this example:

          guix import composer phpunit/phpunit

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

     --repo
          By default, packages are searched in the official OPAM repository.  This option, which can be used more than once, lets you add other repositories which will be searched for packages.  It accepts as valid arguments:

            * the name of a known repository - can be one of opam, coq (equivalent to coq-released), coq-core-dev, coq-extra-dev or grew.

            * the URL of a repository as expected by the opam repository add command (for instance, the URL equivalent of the above opam name would be https://opam.ocaml.org).

            * the path to a local copy of a repository (a directory containing a packages/ sub-directory).

          Repositories are assumed to be passed to this option by order of preference.  The additional repositories will not replace the default opam repository, which is always kept as a fallback.

          Also, please note that versions are not compared across repositories. The first repository (from left to right) that has at least one version of a given package will prevail over any others, and the version imported will be the latest one found in this repository only.

go
     Import metadata for a Go module using proxy.golang.org (https://proxy.golang.org).

          guix import go gopkg.in/yaml.v2

     It is possible to use a package specification with a @VERSION suffix to import a specific version.

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

     --pin-versions
          When using this option, the importer preserves the exact versions of the Go modules dependencies instead of using their latest available versions.  This can be useful when attempting to import packages that recursively depend on former versions of themselves to build.  When using this mode, the symbol of the package is made by appending the version to its name, so that multiple versions of the same package can coexist.

egg
     Import metadata for CHICKEN eggs (https://wiki.call-cc.org/eggs). The information is taken from PACKAGE.egg files found in the eggs-5-all (git://code.call-cc.org/eggs-5-all) Git repository.  However, it does not provide all the information that we need, there is no ``description'' field, and the licenses used are not always precise (BSD is often used instead of BSD-N).

          guix import egg sourcehut

     You can also ask for a specific version:

          guix import egg arrays@1.0

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

hexpm
     Import metadata from the hex.pm Erlang and Elixir package repository hex.pm (https://hex.pm), as in this example:

          guix import hexpm stun

     The importer tries to determine the build system used by the package.

     The hexpm importer also allows you to specify a version string:

          guix import hexpm cf@0.3.0

     Additional options include:

     --recursive
     -r
          Traverse the dependency graph of the given upstream package recursively and generate package expressions for all those packages that are not yet in Guix.

The structure of the guix import code is modular.  It would be useful to have more importers for other package formats, and your help is welcome here (see Contributing).

Invoking guix refresh
=====================

The primary audience of the guix refresh command is packagers. As a user, you may be interested in the --with-latest option, which can bring you package update superpowers built upon guix refresh (see --with-latest).  By default, guix refresh reports any packages provided by the distribution that are outdated compared to the latest upstream version, like this:

     $ guix refresh
     gnu/packages/gettext.scm:29:13: gettext would be upgraded from 0.18.1.1 to 0.18.2.1
     gnu/packages/glib.scm:77:12: glib would be upgraded from 2.34.3 to 2.37.0

Alternatively, one can specify packages to consider, in which case a warning is emitted for packages that lack an updater:

     $ guix refresh coreutils guile guile-ssh
     gnu/packages/ssh.scm:205:2: warning: no updater for guile-ssh
     gnu/packages/guile.scm:136:12: guile would be upgraded from 2.0.12 to 2.0.13

guix refresh browses the upstream repository of each package and determines the highest version number of the releases therein.  The command knows how to update specific types of packages: GNU packages, ELPA packages, etc.---see the documentation for --type below.  There are many packages, though, for which it lacks a method to determine whether a new upstream release is available.  However, the mechanism is extensible, so feel free to get in touch with us to add a new method!

--recursive
     Consider the packages specified, and all the packages upon which they depend.

          $ guix refresh --recursive coreutils
          gnu/packages/acl.scm:40:13: acl would be upgraded from 2.2.53 to 2.3.1
          gnu/packages/m4.scm:30:12: 1.4.18 is already the latest version of m4
          gnu/packages/xml.scm:68:2: warning: no updater for expat
          gnu/packages/multiprecision.scm:40:12: 6.1.2 is already the latest version of gmp
          ...

If for some reason you don't want to update to the latest version, you can update to a specific version by appending an equal sign and the desired version number to the package specification.  Note that not all updaters support this; an error is reported when an updater cannot refresh to the specified version.

     $ guix refresh trytond-party
     gnu/packages/guile.scm:392:2: guile would be upgraded from 3.0.3 to 3.0.5
     $ guix refresh -u guile=3.0.4
     ...
     gnu/packages/guile.scm:392:2: guile: updating from version 3.0.3 to version 3.0.4...
     ...
     $ guix refresh -u guile@2.0=2.0.12
     ...
     gnu/packages/guile.scm:147:2: guile: updating from version 2.0.10 to version 2.0.12...
     ...

In some specific cases, you may have many packages specified via a manifest or a module selection which should all be updated together; for these cases, the --target-version option can be provided to have them all refreshed to the same version, as shown in the examples below:

     $ guix refresh qtbase qtdeclarative --target-version=6.5.2
     gnu/packages/qt.scm:1248:13: qtdeclarative would be upgraded from 6.3.2 to 6.5.2
     gnu/packages/qt.scm:584:2: qtbase would be upgraded from 6.3.2 to 6.5.2

     $ guix refresh --manifest=qt5-manifest.scm --target-version=5.15.10
     gnu/packages/qt.scm:1173:13: qtxmlpatterns would be upgraded from 5.15.8 to 5.15.10
     gnu/packages/qt.scm:1202:13: qtdeclarative would be upgraded from 5.15.8 to 5.15.10
     gnu/packages/qt.scm:1762:13: qtserialbus would be upgraded from 5.15.8 to 5.15.10
     gnu/packages/qt.scm:2070:13: qtquickcontrols2 would be upgraded from 5.15.8 to 5.15.10
     ...

Sometimes the upstream name differs from the package name used in Guix, and guix refresh needs a little help.  Most updaters honor the upstream-name property in package definitions, which can be used to that effect:

     (define-public network-manager
       (package
         (name "network-manager")
         ;; ...
         (properties '((upstream-name . "NetworkManager")))))

When passed --update, it modifies distribution source files to update the version numbers and source code hashes of those package definitions, as well as possibly their inputs (see Defining Packages). This is achieved by downloading each package's latest source tarball and its associated OpenPGP signature, authenticating the downloaded tarball against its signature using gpgv, and finally computing its hash---note that GnuPG must be installed and in $PATH; run guix install gnupg if needed.

When the public key used to sign the tarball is missing from the user's keyring, an attempt is made to automatically retrieve it from a public key server; when this is successful, the key is added to the user's keyring; otherwise, guix refresh reports an error.

The following options are supported:

--expression=EXPR
-e EXPR
     Consider the package EXPR evaluates to.

     This is useful to precisely refer to a package, as in this example:

          guix refresh -l -e '(@@ (gnu packages commencement) glibc-final)'

     This command lists the dependents of the ``final'' libc (essentially all the packages).

--update
-u
     Update distribution source files (package definitions) in place.  This is usually run from a checkout of the Guix source tree (see Running Guix Before It Is Installed):

          ./pre-inst-env guix refresh -s non-core -u

     See Defining Packages, for more information on package definitions. You can also run it on packages from a third-party channel:

          guix refresh -L /path/to/channel -u PACKAGE

     See Creating a Channel, on how to create a channel.

     This command updates the version and source code hash of the package. Depending on the updater being used, it can also update the various inputs fields of the package.  In some cases, the updater might get inputs wrong---it might not know about an extra input that's necessary, or it might add an input that should be avoided.

     To address that, packagers can add properties stating inputs that should be added to those found by the updater or inputs that should be ignored: the updater-extra-inputs and updater-ignored-inputs properties pertain to ``regular'' inputs, and there are equivalent properties for native and propagated inputs.  In the example below, we tell the updater that we need openmpi as an additional input:

          (define-public python-mpi4py
            (package
              (name "python-mpi4py")
              ;; ...
              (inputs (list openmpi))
              (properties
               '((updater-extra-inputs . ("openmpi"))))))

     That way, guix refresh -u python-mpi4py will leave the openmpi input, even if it is not among the inputs it would normally add.

--select=[SUBSET]
-s SUBSET
     Select all the packages in SUBSET, one of core, non-core or module:NAME.

     The core subset refers to all the packages at the core of the distribution---i.e., packages that are used to build ``everything else''.  This includes GCC, libc, Binutils, Bash, etc.  Usually, changing one of these packages in the distribution entails a rebuild of all the others.  Thus, such updates are an inconvenience to users in terms of build time or bandwidth used to achieve the upgrade.

     The non-core subset refers to the remaining packages.  It is typically useful in cases where an update of the core packages would be inconvenient.

     The module:NAME subset refers to all the packages in a specified guile module.  The module can be specified as module:guile or module:(gnu packages guile), the former is a shorthand for the later.

--manifest=FILE
-m FILE
     Select all the packages from the manifest in FILE.  This is useful to check if any packages of the user manifest can be updated.

--type=UPDATER
-t UPDATER
     Select only packages handled by UPDATER (may be a comma-separated list of updaters).  Currently, UPDATER may be one of:

     gnu
          the updater for GNU packages;

     savannah
          the updater for packages hosted at Savannah (https://savannah.gnu.org);

     sourceforge
          the updater for packages hosted at SourceForge (https://sourceforge.net);

     gnome
          the updater for GNOME packages;

     kde
          the updater for KDE packages;

     xorg
          the updater for X.org packages;

     kernel.org
          the updater for packages hosted on kernel.org;

     egg
          the updater for Egg (https://wiki.call-cc.org/eggs/) packages;

     elpa
          the updater for ELPA (https://elpa.gnu.org/) packages;

     cran
          the updater for CRAN (https://cran.r-project.org/) packages;

     bioconductor
          the updater for Bioconductor (https://www.bioconductor.org/) R packages;

     cpan
          the updater for CPAN (https://www.cpan.org/) packages;

     pypi
          the updater for PyPI (https://pypi.python.org) packages.

     gem
          the updater for RubyGems (https://rubygems.org) packages.

     github
          the updater for GitHub (https://github.com) packages.

     hackage
          the updater for Hackage (https://hackage.haskell.org) packages.

     stackage
          the updater for Stackage (https://www.stackage.org) packages.

     crate
          the updater for Crates (https://crates.io) packages.

     launchpad
          the updater for Launchpad (https://launchpad.net) packages.

     generic-html
          a generic updater that crawls the HTML page where the source tarball of the package is hosted, when applicable, or the HTML page specified by the release-monitoring-url property of the package.

     generic-git
          a generic updater for packages hosted on Git repositories.  It tries to be smart about parsing Git tag names, but if it is not able to parse the tag name and compare tags correctly, users can define the following properties for a package.

            * release-tag-prefix: a regular expression for matching a prefix of the tag name.

            * release-tag-suffix: a regular expression for matching a suffix of the tag name.

            * release-tag-version-delimiter: a string used as the delimiter in the tag name for separating the numbers of the version.

            * accept-pre-releases: by default, the updater will ignore pre-releases; to make it also look for pre-releases, set the this property to #t.

               (package
                 (name "foo")
                 ;; ...
                 (properties
                   '((release-tag-prefix . "^release0-")
                     (release-tag-suffix . "[a-z]?$")
                     (release-tag-version-delimiter . ":"))))

     For instance, the following command only checks for updates of Emacs packages hosted at elpa.gnu.org and for updates of CRAN packages:

          $ guix refresh --type=elpa,cran
          gnu/packages/statistics.scm:819:13: r-testthat would be upgraded from 0.10.0 to 0.11.0
          gnu/packages/emacs.scm:856:13: emacs-auctex would be upgraded from 11.88.6 to 11.88.9

--list-updaters
     List available updaters and exit (see --type above).

     For each updater, display the fraction of packages it covers; at the end, display the fraction of packages covered by all these updaters.

In addition, guix refresh can be passed one or more package names, as in this example:

     $ ./pre-inst-env guix refresh -u emacs idutils gcc@4.8

The command above specifically updates the emacs and idutils packages.  The --select option would have no effect in this case.  You might also want to update definitions that correspond to the packages installed in your profile:

     $ ./pre-inst-env guix refresh -u \
            $(guix package --list-installed | cut -f1)

When considering whether to upgrade a package, it is sometimes convenient to know which packages would be affected by the upgrade and should be checked for compatibility.  For this the following option may be used when passing guix refresh one or more package names:

--list-dependent
-l
     List top-level dependent packages that would need to be rebuilt as a result of upgrading one or more packages.

     See the reverse-package type of guix graph, for information on how to visualize the list of dependents of a package.

Be aware that the --list-dependent option only approximates the rebuilds that would be required as a result of an upgrade.  More rebuilds might be required under some circumstances.

     $ guix refresh --list-dependent flex
     Building the following 120 packages would ensure 213 dependent packages are rebuilt:
     hop@2.4.0 emacs-geiser@0.13 notmuch@0.18 mu@0.9.9.5 cflow@1.4 idutils@4.6 ...

The command above lists a set of packages that could be built to check for compatibility with an upgraded flex package.

--list-transitive
-T
     List all the packages which one or more packages depend upon.

          $ guix refresh --list-transitive flex
          flex@2.6.4 depends on the following 25 packages: perl@5.28.0 help2man@1.47.6
          bison@3.0.5 indent@2.2.10 tar@1.30 gzip@1.9 bzip2@1.0.6 xz@5.2.4 file@5.33 ...

The command above lists a set of packages which, when changed, would cause flex to be rebuilt.

The following options can be used to customize GnuPG operation:

--gpg=COMMAND
     Use COMMAND as the GnuPG 2.x command.  COMMAND is searched for in $PATH.

--keyring=FILE
     Use FILE as the keyring for upstream keys.  FILE must be in the keybox format.  Keybox files usually have a name ending in .kbx and the GNU Privacy Guard (GPG) can manipulate these files (see kbxutil (Using the GNU Privacy Guard), for information on a tool to manipulate keybox files).

     When this option is omitted, guix refresh uses ~/.config/guix/upstream/trustedkeys.kbx as the keyring for upstream signing keys.  OpenPGP signatures are checked against keys from this keyring; missing keys are downloaded to this keyring as well (see --key-download below).

     You can export keys from your default GPG keyring into a keybox file using commands like this one:

          gpg --export rms@gnu.org | kbxutil --import-openpgp >> mykeyring.kbx

     Likewise, you can fetch keys to a specific keybox file like this:

          gpg --no-default-keyring --keyring mykeyring.kbx \
            --recv-keys 3CE464558A84FDC69DB40CFB090B11993D9AEBB5

     See --keyring (Using the GNU Privacy Guard), for more information on GPG's --keyring option.

--key-download=POLICY
     Handle missing OpenPGP keys according to POLICY, which may be one of:

     always
          Always download missing OpenPGP keys from the key server, and add them to the user's GnuPG keyring.

     never
          Never try to download missing OpenPGP keys.  Instead just bail out.

     interactive
          When a package signed with an unknown OpenPGP key is encountered, ask the user whether to download it or not.  This is the default behavior.

--key-server=HOST
     Use HOST as the OpenPGP key server when importing a public key.

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

     This allows users to define their own packages and make them visible to the command-line tools.

The github updater uses the GitHub API (https://developer.github.com/v3/) to query for new releases.  When used repeatedly e.g. when refreshing all packages, GitHub will eventually refuse to answer any further API requests.  By default 60 API requests per hour are allowed, and a full refresh on all GitHub packages in Guix requires more than this.  Authentication with GitHub through the use of an API token alleviates these limits.  To use an API token, set the environment variable GUIX_GITHUB_TOKEN to a token procured from https://github.com/settings/tokens or otherwise.

Invoking guix style
===================

The guix style command helps users and packagers alike style their package definitions and configuration files according to the latest fashionable trends.  It can either reformat whole files, with the --whole-file option, or apply specific styling rules to individual package definitions.  The command currently provides the following styling rules:

  * formatting package definitions according to the project's conventions (see Formatting Code);

  * rewriting package inputs to the ``new style'', as explained below.

The way package inputs are written is going through a transition (see package Reference, for more on package inputs).  Until version 1.3.0, package inputs were written using the ``old style'', where each input was given an explicit label, most of the time the package name:

     (package
       ;; ...
       ;; The "old style" (deprecated).
       (inputs `(("libunistring" ,libunistring)
                 ("libffi" ,libffi))))

Today, the old style is deprecated and the preferred style looks like this:

     (package
       ;; ...
       ;; The "new style".
       (inputs (list libunistring libffi)))

Likewise, uses of alist-delete and friends to manipulate inputs is now deprecated in favor of modify-inputs (see Defining Package Variants, for more info on modify-inputs).

In the vast majority of cases, this is a purely mechanical change on the surface syntax that does not even incur a package rebuild.  Running guix style -S inputs can do that for you, whether you're working on packages in Guix proper or in an external channel.

The general syntax is:

     guix style [OPTIONS] PACKAGE...

This causes guix style to analyze and rewrite the definition of PACKAGE... or, when PACKAGE is omitted, of all the packages.  The --styling or -S option allows you to select the style rule, the default rule being format---see below.

To reformat entire source files, the syntax is:

     guix style --whole-file FILE...

The available options are listed below.

--dry-run
-n
     Show source file locations that would be edited but do not modify them.

--whole-file
-f
     Reformat the given files in their entirety.  In that case, subsequent arguments are interpreted as file names (rather than package names), and the --styling option has no effect.

     As an example, here is how you might reformat your operating system configuration (you need write permissions for the file):

          guix style -f /etc/config.scm

--styling=RULE
-S RULE
     Apply RULE, one of the following styling rules:

     format
          Format the given package definition(s)---this is the default styling rule.  For example, a packager running Guix on a checkout (see Running Guix Before It Is Installed) might want to reformat the definition of the Coreutils package like so:

               ./pre-inst-env guix style coreutils

     inputs
          Rewrite package inputs to the ``new style'', as described above.  This is how you would rewrite inputs of package whatnot in your own channel:

               guix style -L ~/my/channel -S inputs whatnot

          Rewriting is done in a conservative way: preserving comments and bailing out if it cannot make sense of the code that appears in an inputs field. The --input-simplification option described below provides fine-grain control over when inputs should be simplified.

     arguments
          Rewrite package arguments to use G-expressions (see G-Expressions). For example, consider this package definition:

               (define-public my-package
                 (package
                   ;; ...
                   (arguments      ;old-style quoted arguments
                    '(#:make-flags '("V=1")
                      #:phases (modify-phases %standard-phases
                                 (delete 'build))))))

          Running guix style -S arguments on this package would rewrite its arguments field like to:

               (define-public my-package
                 (package
                   ;; ...
                   (arguments
                     (list #:make-flags #~'("V=1")
                           #:phases #~(modify-phases %standard-phases
                                        (delete 'build))))))

          Note that changes made by the arguments rule do not entail a rebuild of the affected packages.  Furthermore, if a package definition happens to be using G-expressions already, guix style leaves it unchanged.

--list-stylings
-l
     List and describe the available styling rules and exit.

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

--expression=EXPR
-e EXPR
     Style the package EXPR evaluates to.

     For example, running:

          guix style -e '(@ (gnu packages gcc) gcc-5)'

     styles the gcc-5 package definition.

--input-simplification=POLICY
     When using the inputs styling rule, with -S inputs, this option specifies the package input simplification policy for cases where an input label does not match the corresponding package name. POLICY may be one of the following:

     silent
          Simplify inputs only when the change is ``silent'', meaning that the package does not need to be rebuilt (its derivation is unchanged).

     safe
          Simplify inputs only when that is ``safe'' to do: the package might need to be rebuilt, but the change is known to have no observable effect.

     always
          Simplify inputs even when input labels do not match package names, and even if that might have an observable effect.

     The default is silent, meaning that input simplifications do not trigger any package rebuild.

Invoking guix lint
==================

The guix lint command is meant to help package developers avoid common errors and use a consistent style.  It runs a number of checks on a given set of packages in order to find common mistakes in their definitions.  Available checkers include (see --list-checkers for a complete list):

synopsis
description
     Validate certain typographical and stylistic rules about package descriptions and synopses.

inputs-should-be-native
     Identify inputs that should most likely be native inputs.

source
home-page
mirror-url
github-url
source-file-name
     Probe home-page and source URLs and report those that are invalid.  Suggest a mirror:// URL when applicable.  If the source URL redirects to a GitHub URL, recommend usage of the GitHub URL.  Check that the source file name is meaningful, e.g. is not just a version number or ``git-checkout'', without a declared file-name (see origin Reference).

source-unstable-tarball
     Parse the source URL to determine if a tarball from GitHub is autogenerated or if it is a release tarball.  Unfortunately GitHub's autogenerated tarballs are sometimes regenerated.

derivation
     Check that the derivation of the given packages can be successfully computed for all the supported systems (see Derivations).

profile-collisions
     Check whether installing the given packages in a profile would lead to collisions.  Collisions occur when several packages with the same name but a different version or a different store file name are propagated. See propagated-inputs, for more information on propagated inputs.

archival
     Checks whether the package's source code is archived at Software Heritage (https://www.softwareheritage.org).

     When the source code that is not archived comes from a version-control system (VCS)---e.g., it's obtained with git-fetch, send Software Heritage a ``save'' request so that it eventually archives it.  This ensures that the source will remain available in the long term, and that Guix can fall back to Software Heritage should the source code disappear from its original host. The status of recent ``save'' requests can be viewed on-line (https://archive.softwareheritage.org/save/#requests).

     When source code is a tarball obtained with url-fetch, simply print a message when it is not archived.  As of this writing, Software Heritage does not allow requests to save arbitrary tarballs; we are working on ways to ensure that non-VCS source code is also archived.

     Software Heritage limits the request rate per IP address (https://archive.softwareheritage.org/api/#rate-limiting).  When the limit is reached, guix lint prints a message and the archival checker stops doing anything until that limit has been reset.

cve
     Report known vulnerabilities found in the Common Vulnerabilities and Exposures (CVE) databases of the current and past year published by the US NIST (https://nvd.nist.gov/vuln/data-feeds).

     To view information about a particular vulnerability, visit pages such as:

       * https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-YYYY-ABCD

       * https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-YYYY-ABCD

     where CVE-YYYY-ABCD is the CVE identifier---e.g., CVE-2015-7554.

     Package developers can specify in package recipes the Common Platform Enumeration (CPE) (https://nvd.nist.gov/products/cpe) name and version of the package when they differ from the name or version that Guix uses, as in this example:

          (package
            (name "grub")
            ;; ...
            ;; CPE calls this package "grub2".
            (properties '((cpe-name . "grub2")
                          (cpe-version . "2.3"))))

     Some entries in the CVE database do not specify which version of a package they apply to, and would thus ``stick around'' forever.  Package developers who found CVE alerts and verified they can be ignored can declare them as in this example:

          (package
            (name "t1lib")
            ;; ...
            ;; These CVEs no longer apply and can be safely ignored.
            (properties `((lint-hidden-cve . ("CVE-2011-0433"
                                              "CVE-2011-1553"
                                              "CVE-2011-1554"
                                              "CVE-2011-5244")))))

formatting
     Warn about obvious source code formatting issues: trailing white space, use of tabulations, etc.

input-labels
     Report old-style input labels that do not match the name of the corresponding package.  This aims to help migrate from the ``old input style''.  See package Reference, for more information on package inputs and input styles.  See Invoking guix style, on how to migrate to the new style.

The general syntax is:

     guix lint OPTIONS PACKAGE...

If no package is given on the command line, then all packages are checked. The OPTIONS may be zero or more of the following:

--list-checkers
-l
     List and describe all the available checkers that will be run on packages and exit.

--checkers
-c
     Only enable the checkers specified in a comma-separated list using the names returned by --list-checkers.

--exclude
-x
     Only disable the checkers specified in a comma-separated list using the names returned by --list-checkers.

--expression=EXPR
-e EXPR
     Consider the package EXPR evaluates to.

     This is useful to unambiguously designate packages, as in this example:

          guix lint -c archival -e '(@ (gnu packages guile) guile-3.0)'

--no-network
-n
     Only enable the checkers that do not depend on Internet access.

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

     This allows users to define their own packages and make them visible to the command-line tools.

Invoking guix size
==================

The guix size command helps package developers profile the disk usage of packages.  It is easy to overlook the impact of an additional dependency added to a package, or the impact of using a single output for a package that could easily be split (see Packages with Multiple Outputs).  Such are the typical issues that guix size can highlight.

The command can be passed one or more package specifications such as gcc@4.8 or guile:debug, or a file name in the store.  Consider this example:

     $ guix size coreutils
     store item                               total    self
     /gnu/store/...-gcc-5.5.0-lib           60.4    30.1  38.1%
     /gnu/store/...-glibc-2.27              30.3    28.8  36.6%
     /gnu/store/...-coreutils-8.28          78.9    15.0  19.0%
     /gnu/store/...-gmp-6.1.2               63.1     2.7   3.4%
     /gnu/store/...-bash-static-4.4.12       1.5     1.5   1.9%
     /gnu/store/...-acl-2.2.52              61.1     0.4   0.5%
     /gnu/store/...-attr-2.4.47             60.6     0.2   0.3%
     /gnu/store/...-libcap-2.25             60.5     0.2   0.2%
     total: 78.9 MiB

The store items listed here constitute the transitive closure of Coreutils---i.e., Coreutils and all its dependencies, recursively---as would be returned by:

     $ guix gc -R /gnu/store/...-coreutils-8.23

Here the output shows three columns next to store items.  The first column, labeled ``total'', shows the size in mebibytes (MiB) of the closure of the store item---that is, its own size plus the size of all its dependencies.  The next column, labeled ``self'', shows the size of the item itself.  The last column shows the ratio of the size of the item itself to the space occupied by all the items listed here.

In this example, we see that the closure of Coreutils weighs in at 79 MiB, most of which is taken by libc and GCC's run-time support libraries.  (That libc and GCC's libraries represent a large fraction of the closure is not a problem per se because they are always available on the system anyway.)

Since the command also accepts store file names, assessing the size of a build result is straightforward:

     guix size $(guix system build config.scm)

When the package(s) passed to guix size are available in the store (More precisely, guix size looks for the ungrafted variant of the given package(s), as returned by guix build PACKAGE --no-grafts.  See Security Updates, for information on grafts.), guix size queries the daemon to determine its dependencies, and measures its size in the store, similar to du -ms --apparent-size (see du invocation (GNU Coreutils)).

When the given packages are not in the store, guix size reports information based on the available substitutes (see Substitutes).  This makes it possible to profile the disk usage of store items that are not even on disk, only available remotely.

You can also specify several package names:

     $ guix size coreutils grep sed bash
     store item                               total    self
     /gnu/store/...-coreutils-8.24          77.8    13.8  13.4%
     /gnu/store/...-grep-2.22               73.1     0.8   0.8%
     /gnu/store/...-bash-4.3.42             72.3     4.7   4.6%
     /gnu/store/...-readline-6.3            67.6     1.2   1.2%
     ...
     total: 102.3 MiB

In this example we see that the combination of the four packages takes 102.3 MiB in total, which is much less than the sum of each closure since they have a lot of dependencies in common.

When looking at the profile returned by guix size, you may find yourself wondering why a given package shows up in the profile at all.  To understand it, you can use guix graph --path -t references to display the shortest path between the two packages (see Invoking guix graph).

The available options are:

--substitute-urls=URLS
     Use substitute information from URLS. See the same option for guix build.

--sort=KEY
     Sort lines according to KEY, one of the following options:

     self
          the size of each item (the default);

     closure
          the total size of the item's closure.

--map-file=FILE
     Write a graphical map of disk usage in PNG format to FILE.

     For the example above, the map looks like this:

     map of Coreutils disk usage produced by guix size

     This option requires that Guile-Charting (https://wingolog.org/software/guile-charting/) be installed and visible in Guile's module search path.  When that is not the case, guix size fails as it tries to load it.

--system=SYSTEM
-s SYSTEM
     Consider packages for SYSTEM---e.g., x86_64-linux.

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

     This allows users to define their own packages and make them visible to the command-line tools.

Invoking guix graph
===================

Packages and their dependencies form a graph, specifically a directed acyclic graph (DAG).  It can quickly become difficult to have a mental model of the package DAG, so the guix graph command provides a visual representation of the DAG.  By default, guix graph emits a DAG representation in the input format of Graphviz (https://www.graphviz.org/), so its output can be passed directly to the dot command of Graphviz.  It can also emit an HTML page with embedded JavaScript code to display a ``chord diagram'' in a Web browser, using the d3.js (https://d3js.org/) library, or emit Cypher queries to construct a graph in a graph database supporting the openCypher (https://www.opencypher.org/) query language.  With --path, it simply displays the shortest path between two packages.  The general syntax is:

     guix graph OPTIONS PACKAGE...

For example, the following command generates a PDF file representing the package DAG for the GNU Core Utilities, showing its build-time dependencies:

     guix graph coreutils | dot -Tpdf > dag.pdf

The output looks like this:

Dependency graph of the GNU Coreutils

Nice little graph, no?

You may find it more pleasant to navigate the graph interactively with xdot (from the xdot package):

     guix graph coreutils | xdot -

But there is more than one graph!  The one above is concise: it is the graph of package objects, omitting implicit inputs such as GCC, libc, grep, etc.  It is often useful to have such a concise graph, but sometimes one may want to see more details.  guix graph supports several types of graphs, allowing you to choose the level of detail:

package
     This is the default type used in the example above.  It shows the DAG of package objects, excluding implicit dependencies.  It is concise, but filters out many details.

reverse-package
     This shows the reverse DAG of packages.  For example:

          guix graph --type=reverse-package ocaml

     ... yields the graph of packages that explicitly depend on OCaml (if you are also interested in cases where OCaml is an implicit dependency, see reverse-bag below).

     Note that for core packages this can yield huge graphs.  If all you want is to know the number of packages that depend on a given package, use guix refresh --list-dependent (see --list-dependent).

bag-emerged
     This is the package DAG, including implicit inputs.

     For instance, the following command:

          guix graph --type=bag-emerged coreutils

     ... yields this bigger graph:

     Detailed dependency graph of the GNU Coreutils

     At the bottom of the graph, we see all the implicit inputs of GNU-BUILD-SYSTEM (see gnu-build-system).

     Now, note that the dependencies of these implicit inputs---that is, the bootstrap dependencies (see Bootstrapping)---are not shown here, for conciseness.

bag
     Similar to bag-emerged, but this time including all the bootstrap dependencies.

bag-with-origins
     Similar to bag, but also showing origins and their dependencies.

reverse-bag
     This shows the reverse DAG of packages.  Unlike reverse-package, it also takes implicit dependencies into account.  For example:

          guix graph -t reverse-bag dune

     ... yields the graph of all packages that depend on Dune, directly or indirectly.  Since Dune is an implicit dependency of many packages via dune-build-system, this shows a large number of packages, whereas reverse-package would show very few if any.

derivation
     This is the most detailed representation: It shows the DAG of derivations (see Derivations) and plain store items.  Compared to the above representation, many additional nodes are visible, including build scripts, patches, Guile modules, etc.

     For this type of graph, it is also possible to pass a .drv file name instead of a package name, as in:

          guix graph -t derivation $(guix system build -d my-config.scm)

module
     This is the graph of package modules (see Package Modules). For example, the following command shows the graph for the package module that defines the guile package:

          guix graph -t module guile | xdot -

All the types above correspond to build-time dependencies.  The following graph type represents the run-time dependencies:

references
     This is the graph of references of a package output, as returned by guix gc --references (see Invoking guix gc).

     If the given package output is not available in the store, guix graph attempts to obtain dependency information from substitutes.

     Here you can also pass a store file name instead of a package name.  For example, the command below produces the reference graph of your profile (which can be big!):

          guix graph -t references $(readlink -f ~/.guix-profile)

referrers
     This is the graph of the referrers of a store item, as returned by guix gc --referrers (see Invoking guix gc).

     This relies exclusively on local information from your store.  For instance, let us suppose that the current Inkscape is available in 10 profiles on your machine; guix graph -t referrers inkscape will show a graph rooted at Inkscape and with those 10 profiles linked to it.

     It can help determine what is preventing a store item from being garbage collected.

Often, the graph of the package you are interested in does not fit on your screen, and anyway all you want to know is why that package actually depends on some seemingly unrelated package.  The --path option instructs guix graph to display the shortest path between two packages (or derivations, or store items, etc.):

     $ guix graph --path emacs libunistring
     emacs@26.3
     mailutils@3.9
     libunistring@0.9.10
     $ guix graph --path -t derivation emacs libunistring
     /gnu/store/...-emacs-26.3.drv
     /gnu/store/...-mailutils-3.9.drv
     /gnu/store/...-libunistring-0.9.10.drv
     $ guix graph --path -t references emacs libunistring
     /gnu/store/...-emacs-26.3
     /gnu/store/...-libidn2-2.2.0
     /gnu/store/...-libunistring-0.9.10

Sometimes you still want to visualize the graph but would like to trim it so it can actually be displayed.  One way to do it is via the --max-depth (or -M) option, which lets you specify the maximum depth of the graph.  In the example below, we visualize only libreoffice and the nodes whose distance to libreoffice is at most 2:

     guix graph -M 2 libreoffice | xdot -f fdp -

Mind you, that's still a big ball of spaghetti, but at least dot can render it quickly and it can be browsed somewhat.

The available options are the following:

--type=TYPE
-t TYPE
     Produce a graph output of TYPE, where TYPE must be one of the values listed above.

--list-types
     List the supported graph types.

--backend=BACKEND
-b BACKEND
     Produce a graph using the selected BACKEND.

--list-backends
     List the supported graph backends.

     Currently, the available backends are Graphviz and d3.js.

--path
     Display the shortest path between two nodes of the type specified by --type.  The example below shows the shortest path between libreoffice and llvm according to the references of libreoffice:

          $ guix graph --path -t references libreoffice llvm
          /gnu/store/...-libreoffice-6.4.2.2
          /gnu/store/...-libepoxy-1.5.4
          /gnu/store/...-mesa-19.3.4
          /gnu/store/...-llvm-9.0.1

--expression=EXPR
-e EXPR
     Consider the package EXPR evaluates to.

     This is useful to precisely refer to a package, as in this example:

          guix graph -e '(@@ (gnu packages commencement) gnu-make-final)'

--system=SYSTEM
-s SYSTEM
     Display the graph for SYSTEM---e.g., i686-linux.

     The package dependency graph is largely architecture-independent, but there are some architecture-dependent bits that this option allows you to visualize.

--load-path=DIRECTORY
-L DIRECTORY
     Add DIRECTORY to the front of the package module search path (see Package Modules).

     This allows users to define their own packages and make them visible to the command-line tools.

On top of that, guix graph supports all the usual package transformation options (see Package Transformation Options).  This makes it easy to view the effect of a graph-rewriting transformation such as --with-input.  For example, the command below outputs the graph of git once openssl has been replaced by libressl everywhere in the graph:

     guix graph git --with-input=openssl=libressl

So many possibilities, so much fun!

Invoking guix publish
=====================

The purpose of guix publish is to enable users to easily share their store with others, who can then use it as a substitute server (see Substitutes).

When guix publish runs, it spawns an HTTP server which allows anyone with network access to obtain substitutes from it.  This means that any machine running Guix can also act as if it were a build farm, since the HTTP interface is compatible with Cuirass, the software behind the ci.guix.gnu.org build farm.

For security, each substitute is signed, allowing recipients to check their authenticity and integrity (see Substitutes).  Because guix publish uses the signing key of the system, which is only readable by the system administrator, it must be started as root; the --user option makes it drop root privileges early on.

The signing key pair must be generated before guix publish is launched, using guix archive --generate-key (see Invoking guix archive).

When the --advertise option is passed, the server advertises its availability on the local network using multicast DNS (mDNS) and DNS service discovery (DNS-SD), currently via Guile-Avahi (see Using Avahi in Guile Scheme Programs).

The general syntax is:

     guix publish OPTIONS...

Running guix publish without any additional arguments will spawn an HTTP server on port 8080:

     guix publish

guix publish can also be started following the systemd ``socket activation'' protocol (see make-systemd-constructor (The GNU Shepherd Manual)).

Once a publishing server has been authorized, the daemon may download substitutes from it.  See Getting Substitutes from Other Servers.

By default, guix publish compresses archives on the fly as it serves them.  This ``on-the-fly'' mode is convenient in that it requires no setup and is immediately available.  However, when serving lots of clients, we recommend using the --cache option, which enables caching of the archives before they are sent to clients---see below for details.  The guix weather command provides a handy way to check what a server provides (see Invoking guix weather).

As a bonus, guix publish also serves as a content-addressed mirror for source files referenced in origin records (see origin Reference).  For instance, assuming guix publish is running on example.org, the following URL returns the raw hello-2.10.tar.gz file with the given SHA256 hash (represented in nix-base32 format, see Invoking guix hash):

     http://example.org/file/hello-2.10.tar.gz/sha256/0ssi1...ndq1i

Obviously, these URLs only work for files that are in the store; in other cases, they return 404 (``Not Found'').

Build logs are available from /log URLs like:

     http://example.org/log/gwspk...-guile-2.2.3

When guix-daemon is configured to save compressed build logs, as is the case by default (see Invoking guix-daemon), /log URLs return the compressed log as-is, with an appropriate Content-Type and/or Content-Encoding header.  We recommend running guix-daemon with --log-compression=gzip since Web browsers can automatically decompress it, which is not the case with Bzip2 compression.

The following options are available:

--port=PORT
-p PORT
     Listen for HTTP requests on PORT.

--listen=HOST
     Listen on the network interface for HOST.  The default is to accept connections from any interface.

--user=USER
-u USER
     Change privileges to USER as soon as possible---i.e., once the server socket is open and the signing key has been read.

--compression[=METHOD[:LEVEL]]
-C [METHOD[:LEVEL]]
     Compress data using the given METHOD and LEVEL.  METHOD is one of lzip, zstd, and gzip; when METHOD is omitted, gzip is used.

     When LEVEL is zero, disable compression.  The range 1 to 9 corresponds to different compression levels: 1 is the fastest, and 9 is the best (CPU-intensive).  The default is 3.

     Usually, lzip compresses noticeably better than gzip for a small increase in CPU usage; see benchmarks on the lzip Web page (https://nongnu.org/lzip/lzip_benchmark.html).  However, lzip achieves low decompression throughput (on the order of 50 MiB/s on modern hardware), which can be a bottleneck for someone who downloads over a fast network connection.

     The compression ratio of zstd is between that of lzip and that of gzip; its main advantage is a high decompression speed (https://facebook.github.io/zstd/).

     Unless --cache is used, compression occurs on the fly and the compressed streams are not cached.  Thus, to reduce load on the machine that runs guix publish, it may be a good idea to choose a low compression level, to run guix publish behind a caching proxy, or to use --cache.  Using --cache has the advantage that it allows guix publish to add Content-Length HTTP header to its responses.

     This option can be repeated, in which case every substitute gets compressed using all the selected methods, and all of them are advertised.  This is useful when users may not support all the compression methods: they can select the one they support.

--cache=DIRECTORY
-c DIRECTORY
     Cache archives and meta-data (.narinfo URLs) to DIRECTORY and only serve archives that are in cache.

     When this option is omitted, archives and meta-data are created on-the-fly.  This can reduce the available bandwidth, especially when compression is enabled, since this may become CPU-bound.  Another drawback of the default mode is that the length of archives is not known in advance, so guix publish does not add a Content-Length HTTP header to its responses, which in turn prevents clients from knowing the amount of data being downloaded.

     Conversely, when --cache is used, the first request for a store item (via a .narinfo URL) triggers a background process to bake the archive---computing its .narinfo and compressing the archive, if needed.  Once the archive is cached in DIRECTORY, subsequent requests succeed and are served directly from the cache, which guarantees that clients get the best possible bandwidth.

     That first .narinfo request nonetheless returns 200, provided the requested store item is ``small enough'', below the cache bypass threshold---see --cache-bypass-threshold below.  That way, clients do not have to wait until the archive is baked.  For larger store items, the first .narinfo request returns 404, meaning that clients have to wait until the archive is baked.

     The ``baking'' process is performed by worker threads.  By default, one thread per CPU core is created, but this can be customized.  See --workers below.

     When --ttl is used, cached entries are automatically deleted when they have expired.

--workers=N
     When --cache is used, request the allocation of N worker threads to ``bake'' archives.

--ttl=TTL
     Produce Cache-Control HTTP headers that advertise a time-to-live (TTL) of TTL.  TTL must denote a duration: 5d means 5 days, 1m means 1 month, and so on.

     This allows the user's Guix to keep substitute information in cache for TTL.  However, note that guix publish does not itself guarantee that the store items it provides will indeed remain available for as long as TTL.

     Additionally, when --cache is used, cached entries that have not been accessed for TTL and that no longer have a corresponding item in the store, may be deleted.

--negative-ttl=TTL
     Similarly produce Cache-Control HTTP headers to advertise the time-to-live (TTL) of negative lookups---missing store items, for which the HTTP 404 code is returned.  By default, no negative TTL is advertised.

     This parameter can help adjust server load and substitute latency by instructing cooperating clients to be more or less patient when a store item is missing.

--cache-bypass-threshold=SIZE
     When used in conjunction with --cache, store items smaller than SIZE are immediately available, even when they are not yet in cache.  SIZE is a size in bytes, or it can be suffixed by M for megabytes and so on.  The default is 10M.

     ``Cache bypass'' allows you to reduce the publication delay for clients at the expense of possibly additional I/O and CPU use on the server side: depending on the client access patterns, those store items can end up being baked several times until a copy is available in cache.

     Increasing the threshold may be useful for sites that have few users, or to guarantee that users get substitutes even for store items that are not popular.

--nar-path=PATH
     Use PATH as the prefix for the URLs of ``nar'' files (see normalized archives).

     By default, nars are served at a URL such as /nar/gzip/...-coreutils-8.25.  This option allows you to change the /nar part to PATH.

--public-key=FILE
--private-key=FILE
     Use the specific FILEs as the public/private key pair used to sign the store items being published.

     The files must correspond to the same key pair (the private key is used for signing and the public key is merely advertised in the signature metadata).  They must contain keys in the canonical s-expression format as produced by guix archive --generate-key (see Invoking guix archive).  By default, /etc/guix/signing-key.pub and /etc/guix/signing-key.sec are used.

--repl[=PORT]
-r [PORT]
     Spawn a Guile REPL server (see REPL Servers (GNU Guile Reference Manual)) on PORT (37146 by default).  This is used primarily for debugging a running guix publish server.

Enabling guix publish on Guix System is a one-liner: just instantiate a guix-publish-service-type service in the services field of the operating-system declaration (see guix-publish-service-type).

If you are instead running Guix on a ``foreign distro'', follow these instructions:

  * If your host distro uses the systemd init system:

          # ln -s ~root/.guix-profile/lib/systemd/system/guix-publish.service \
                  /etc/systemd/system/
          # systemctl start guix-publish && systemctl enable guix-publish

  * If your host distro uses the Upstart init system:

          # ln -s ~root/.guix-profile/lib/upstart/system/guix-publish.conf /etc/init/
          # start guix-publish

  * Otherwise, proceed similarly with your distro's init system.

Invoking guix challenge
=======================

Do the binaries provided by this server really correspond to the source code it claims to build?  Is a package build process deterministic? These are the questions the guix challenge command attempts to answer.

The former is obviously an important question: Before using a substitute server (see Substitutes), one had better verify that it provides the right binaries, and thus challenge it.  The latter is what enables the former: If package builds are deterministic, then independent builds of the package should yield the exact same result, bit for bit; if a server provides a binary different from the one obtained locally, it may be either corrupt or malicious.

We know that the hash that shows up in /gnu/store file names is the hash of all the inputs of the process that built the file or directory---compilers, libraries, build scripts, etc. (see Introduction).  Assuming deterministic build processes, one store file name should map to exactly one build output. guix challenge checks whether there is, indeed, a single mapping by comparing the build outputs of several independent builds of any given store item.

The command output looks like this:

     $ guix challenge \
       --substitute-urls="https://ci.guix.gnu.org https://guix.example.org" \
       openssl git pius coreutils grep
     updating substitutes from 'https://ci.guix.gnu.org'... 100.0%
     updating substitutes from 'https://guix.example.org'... 100.0%
     /gnu/store/...-openssl-1.0.2d contents differ:
       local hash: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
       https://ci.guix.gnu.org/nar/...-openssl-1.0.2d: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
       https://guix.example.org/nar/...-openssl-1.0.2d: 1zy4fmaaqcnjrzzajkdn3f5gmjk754b43qkq47llbyak9z0qjyim
       differing files:
         /lib/libcrypto.so.1.1
         /lib/libssl.so.1.1

     /gnu/store/...-git-2.5.0 contents differ:
       local hash: 00p3bmryhjxrhpn2gxs2fy0a15lnip05l97205pgbk5ra395hyha
       https://ci.guix.gnu.org/nar/...-git-2.5.0: 069nb85bv4d4a6slrwjdy8v1cn4cwspm3kdbmyb81d6zckj3nq9f
       https://guix.example.org/nar/...-git-2.5.0: 0mdqa9w1p6cmli6976v4wi0sw9r4p5prkj7lzfd1877wk11c9c73
       differing file:
         /libexec/git-core/git-fsck

     /gnu/store/...-pius-2.1.1 contents differ:
       local hash: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
       https://ci.guix.gnu.org/nar/...-pius-2.1.1: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
       https://guix.example.org/nar/...-pius-2.1.1: 1cy25x1a4fzq5rk0pmvc8xhwyffnqz95h2bpvqsz2mpvlbccy0gs
       differing file:
         /share/man/man1/pius.1.gz

     ...

     5 store items were analyzed:
       - 2 (40.0%) were identical
       - 3 (60.0%) differed
       - 0 (0.0%) were inconclusive

In this example, guix challenge queries all the substitute servers for each of the fives packages specified on the command line. It then reports those store items for which the servers obtained a result different from the local build (if it exists) and/or different from one another; here, the local hash lines indicate that a local build result was available for each of these packages and shows its hash.

As an example, guix.example.org always gets a different answer. Conversely, ci.guix.gnu.org agrees with local builds, except in the case of Git.  This might indicate that the build process of Git is non-deterministic, meaning that its output varies as a function of various things that Guix does not fully control, in spite of building packages in isolated environments (see Features).  Most common sources of non-determinism include the addition of timestamps in build results, the inclusion of random numbers, and directory listings sorted by inode number.  See https://reproducible-builds.org/docs/, for more information.

To find out what is wrong with this Git binary, the easiest approach is to run:

     guix challenge git \
       --diff=diffoscope \
       --substitute-urls="https://ci.guix.gnu.org https://guix.example.org"

This automatically invokes diffoscope, which displays detailed information about files that differ.

Alternatively, we can do something along these lines (see Invoking guix archive):

     $ wget -q -O - https://ci.guix.gnu.org/nar/lzip/...-git-2.5.0 \
        | lzip -d | guix archive -x /tmp/git
     $ diff -ur --no-dereference /gnu/store/...-git.2.5.0 /tmp/git

This command shows the difference between the files resulting from the local build, and the files resulting from the build on ci.guix.gnu.org (see Comparing and Merging Files).  The diff command works great for text files.  When binary files differ, a better option is Diffoscope (https://diffoscope.org/), a tool that helps visualize differences for all kinds of files.

Once you have done that work, you can tell whether the differences are due to a non-deterministic build process or to a malicious server.  We try hard to remove sources of non-determinism in packages to make it easier to verify substitutes, but of course, this is a process that involves not just Guix, but a large part of the free software community. In the meantime, guix challenge is one tool to help address the problem.

If you are writing packages for Guix, you are encouraged to check whether ci.guix.gnu.org and other substitute servers obtain the same build result as you did with:

     guix challenge PACKAGE

The general syntax is:

     guix challenge OPTIONS ARGUMENT...

where ARGUMENT is a package specification such as guile@2.0 or glibc:debug or, alternatively, a store file name as returned, for example, by guix build or guix gc --list-live.

When a difference is found between the hash of a locally-built item and that of a server-provided substitute, or among substitutes provided by different servers, the command displays it as in the example above and its exit code is 2 (other non-zero exit codes denote other kinds of errors).

The one option that matters is:

--substitute-urls=URLS
     Consider URLS the whitespace-separated list of substitute source URLs to compare to.

--diff=MODE
     Upon mismatches, show differences according to MODE, one of:

     simple (the default)
          Show the list of files that differ.

     diffoscope
     COMMAND
          Invoke Diffoscope (https://diffoscope.org/), passing it two directories whose contents do not match.

          When COMMAND is an absolute file name, run COMMAND instead of Diffoscope.

     none
          Do not show further details about the differences.

     Thus, unless --diff=none is passed, guix challenge downloads the store items from the given substitute servers so that it can compare them.

--verbose
-v
     Show details about matches (identical contents) in addition to information about mismatches.

Invoking guix copy
==================

The guix copy command copies items from the store of one machine to that of another machine over a secure shell (SSH) connection (This command is available only when Guile-SSH was found.  See Requirements, for details.).  For example, the following command copies the coreutils package, the user's profile, and all their dependencies over to HOST, logged in as USER:

     guix copy --to=USER@HOST \
               coreutils $(readlink -f ~/.guix-profile)

If some of the items to be copied are already present on HOST, they are not actually sent.

The command below retrieves libreoffice and gimp from HOST, assuming they are available there:

     guix copy --from=HOST libreoffice gimp

The SSH connection is established using the Guile-SSH client, which is compatible with OpenSSH: it honors ~/.ssh/known_hosts and ~/.ssh/config, and uses the SSH agent for authentication.

The key used to sign items that are sent must be accepted by the remote machine.  Likewise, the key used by the remote machine to sign items you are retrieving must be in /etc/guix/acl so it is accepted by your own daemon.  See Invoking guix archive, for more information about store item authentication.

The general syntax is:

     guix copy [--to=SPEC|--from=SPEC] ITEMS...

You must always specify one of the following options:

--to=SPEC
--from=SPEC
     Specify the host to send to or receive from.  SPEC must be an SSH spec such as example.org, charlie@example.org, or charlie@example.org:2222.

The ITEMS can be either package names, such as gimp, or store items, such as /gnu/store/...-idutils-4.6.

When specifying the name of a package to send, it is first built if needed, unless --dry-run was specified.  Common build options are supported (see Common Build Options).

Invoking guix container
=======================

     As of version VERSION, this tool is experimental.  The interface is subject to radical change in the future.

The purpose of guix container is to manipulate processes running within an isolated environment, commonly known as a ``container'', typically created by the guix shell (see Invoking guix shell) and guix system container (see Invoking guix system) commands.

The general syntax is:

     guix container ACTION OPTIONS...

ACTION specifies the operation to perform with a container, and OPTIONS specifies the context-specific arguments for the action.

The following actions are available:

exec
     Execute a command within the context of a running container.

     The syntax is:

          guix container exec PID PROGRAM ARGUMENTS...

     PID specifies the process ID of the running container. PROGRAM specifies an executable file name within the root file system of the container.  ARGUMENTS are the additional options that will be passed to PROGRAM.

     The following command launches an interactive login shell inside a Guix system container, started by guix system container, and whose process ID is 9001:

          guix container exec 9001 /run/current-system/profile/bin/bash --login

     Note that the PID cannot be the parent process of a container.  It must be PID 1 of the container or one of its child processes.

Invoking guix weather
=====================

Occasionally you're grumpy because substitutes are lacking and you end up building packages by yourself (see Substitutes).  The guix weather command reports on substitute availability on the specified servers so you can have an idea of whether you'll be grumpy today.  It can sometimes be useful info as a user, but it is primarily useful to people running guix publish (see Invoking guix publish).  Sometimes substitutes are available but they are not authorized on your system; guix weather reports it so you can authorize them if you want (see Getting Substitutes from Other Servers).

Here's a sample run:

     $ guix weather --substitute-urls=https://guix.example.org
     computing 5,872 package derivations for x86_64-linux...
     looking for 6,128 store items on https://guix.example.org..
     updating substitutes from 'https://guix.example.org'... 100.0%
     https://guix.example.org
       43.4% substitutes available (2,658 out of 6,128)
       7,032.5 MiB of nars (compressed)
       19,824.2 MiB on disk (uncompressed)
       0.030 seconds per request (182.9 seconds in total)
       33.5 requests per second

       9.8% (342 out of 3,470) of the missing items are queued
       867 queued builds
           x86_64-linux: 518 (59.7%)
           i686-linux: 221 (25.5%)
           aarch64-linux: 128 (14.8%)
       build rate: 23.41 builds per hour
           x86_64-linux: 11.16 builds per hour
           i686-linux: 6.03 builds per hour
           aarch64-linux: 6.41 builds per hour

As you can see, it reports the fraction of all the packages for which substitutes are available on the server---regardless of whether substitutes are enabled, and regardless of whether this server's signing key is authorized.  It also reports the size of the compressed archives (``nars'') provided by the server, the size the corresponding store items occupy in the store (assuming deduplication is turned off), and the server's throughput.  The second part gives continuous integration (CI) statistics, if the server supports it.  In addition, using the --coverage option, guix weather can list ``important'' package substitutes missing on the server (see below).

To achieve that, guix weather queries over HTTP(S) meta-data (narinfos) for all the relevant store items.  Like guix challenge, it ignores signatures on those substitutes, which is innocuous since the command only gathers statistics and cannot install those substitutes.

The general syntax is:

     guix weather OPTIONS... [PACKAGES...]

When PACKAGES is omitted, guix weather checks the availability of substitutes for all the packages, or for those specified with --manifest; otherwise it only considers the specified packages.  It is also possible to query specific system types with --system. guix weather exits with a non-zero code when the fraction of available substitutes is below 100%.

The available options are listed below.

--substitute-urls=URLS
     URLS is the space-separated list of substitute server URLs to query.  When this option is omitted, the URLs specified with the --substitute-urls option of guix-daemon are used or, as a last resort, the default set of substitute URLs.

--system=SYSTEM
-s SYSTEM
     Query substitutes for SYSTEM---e.g., aarch64-linux.  This option can be repeated, in which case guix weather will query substitutes for several system types.

--manifest=FILE
     Instead of querying substitutes for all the packages, only ask for those specified in FILE.  FILE must contain a manifest, as with the -m option of guix package (see Invoking guix package).

     This option can be repeated several times, in which case the manifests are concatenated.

--expression=EXPR
-e EXPR
     Consider the package EXPR evaluates to.

     A typical use case for this option is specifying a package that is hidden and thus cannot be referred to in the usual way, as in this example:

          guix weather -e '(@@ (gnu packages rust) rust-bootstrap)'

     This option can be repeated.

--coverage[=COUNT]
-c [COUNT]
     Report on substitute coverage for packages: list packages with at least COUNT dependents (zero by default) for which substitutes are unavailable.  Dependent packages themselves are not listed: if B depends on A and A has no substitutes, only A is listed, even though B usually lacks substitutes as well.  The result looks like this:

          $ guix weather --substitute-urls=https://ci.guix.gnu.org https://bordeaux.guix.gnu.org -c 10
          computing 8,983 package derivations for x86_64-linux...
          looking for 9,343 store items on https://ci.guix.gnu.org https://bordeaux.guix.gnu.org...
          updating substitutes from 'https://ci.guix.gnu.org https://bordeaux.guix.gnu.org'... 100.0%
          https://ci.guix.gnu.org https://bordeaux.guix.gnu.org
            64.7% substitutes available (6,047 out of 9,343)
          ...
          2502 packages are missing from 'https://ci.guix.gnu.org https://bordeaux.guix.gnu.org' for 'x86_64-linux', among which:
              58  kcoreaddons@5.49.0      /gnu/store/...-kcoreaddons-5.49.0
              46  qgpgme@1.11.1           /gnu/store/...-qgpgme-1.11.1
              37  perl-http-cookiejar@0.008  /gnu/store/...-perl-http-cookiejar-0.008
              ...

     What this example shows is that kcoreaddons and presumably the 58 packages that depend on it have no substitutes at ci.guix.gnu.org; likewise for qgpgme and the 46 packages that depend on it.

     If you are a Guix developer, or if you are taking care of this build farm, you'll probably want to have a closer look at these packages: they may simply fail to build.

--display-missing
     Display the list of store items for which substitutes are missing.

Invoking guix processes
=======================

The guix processes command can be useful to developers and system administrators, especially on multi-user machines and on build farms: it lists the current sessions (connections to the daemon), as well as information about the processes involved (Remote sessions, when guix-daemon is started with --listen specifying a TCP endpoint, are not listed.).  Here's an example of the information it returns:

     $ sudo guix processes
     SessionPID: 19002
     ClientPID: 19090
     ClientCommand: guix shell python

     SessionPID: 19402
     ClientPID: 19367
     ClientCommand: guix publish -u guix-publish -p 3000 -C 9 ...

     SessionPID: 19444
     ClientPID: 19419
     ClientCommand: cuirass --cache-directory /var/cache/cuirass ...
     LockHeld: /gnu/store/...-perl-ipc-cmd-0.96.lock
     LockHeld: /gnu/store/...-python-six-bootstrap-1.11.0.lock
     LockHeld: /gnu/store/...-libjpeg-turbo-2.0.0.lock
     ChildPID: 20495
     ChildCommand: guix offload x86_64-linux 7200 1 28800
     ChildPID: 27733
     ChildCommand: guix offload x86_64-linux 7200 1 28800
     ChildPID: 27793
     ChildCommand: guix offload x86_64-linux 7200 1 28800

In this example we see that guix-daemon has three clients: guix shell, guix publish, and the Cuirass continuous integration tool; their process identifier (PID) is given by the ClientPID field.  The SessionPID field gives the PID of the guix-daemon sub-process of this particular session.

The LockHeld fields show which store items are currently locked by this session, which corresponds to store items being built or substituted (the LockHeld field is not displayed when guix processes is not running as root).  Last, by looking at the ChildPID and ChildCommand fields, we understand that these three builds are being offloaded (see Daemon Offload Setup).

The output is in Recutils format so we can use the handy recsel command to select sessions of interest (see Selection Expressions (GNU recutils manual)).  As an example, the command shows the command line and PID of the client that triggered the build of a Perl package:

     $ sudo guix processes | \
         recsel -p ClientPID,ClientCommand -e 'LockHeld ~ "perl"'
     ClientPID: 19419
     ClientCommand: cuirass --cache-directory /var/cache/cuirass ...

Additional options are listed below.

--format=FORMAT
-f FORMAT
     Produce output in the specified FORMAT, one of:

     recutils
          The default option.  It outputs a set of Session recutils records that include each ChildProcess as a field.

     normalized
          Normalize the output records into record sets (see Record Sets (GNU recutils manual)).  Normalizing into record sets allows joins across record types.  The example below lists the PID of each ChildProcess and the associated PID for Session that spawned the ChildProcess where the Session was started using guix build.

               $ guix processes --format=normalized | \
                   recsel \
                   -j Session \
                   -t ChildProcess \
                   -p Session.PID,PID \
                   -e 'Session.ClientCommand ~ "guix build"'
               PID: 4435
               Session_PID: 4278

               PID: 4554
               Session_PID: 4278

               PID: 4646
               Session_PID: 4278

Foreign Architectures
*********************

You can target computers of different CPU architectures when producing packages (see Invoking guix package), packs (see Invoking guix pack) or full systems (see Invoking guix system).

GNU Guix supports two distinct mechanisms to target foreign architectures:

 1. The traditional cross-compilation (https://en.wikipedia.org/wiki/Cross_compiler) mechanism.

 2. The native building mechanism which consists in building using the CPU instruction set of the foreign system you are targeting.  It often requires emulation, using the QEMU program for instance.

Cross-Compilation
=================

The commands supporting cross-compilation are proposing the --list-targets and --target options.

The --list-targets option lists all the supported targets that can be passed as an argument to --target.

     $ guix build --list-targets
     The available targets are:

        - aarch64-linux-gnu
        - arm-linux-gnueabihf
        - avr
        - i586-pc-gnu
        - i686-linux-gnu
        - i686-w64-mingw32
        - mips64el-linux-gnu
        - or1k-elf
        - powerpc-linux-gnu
        - powerpc64le-linux-gnu
        - riscv64-linux-gnu
        - x86_64-linux-gnu
        - x86_64-w64-mingw32

Targets are specified as GNU triplets (see GNU configuration triplets (Autoconf)).

Those triplets are passed to GCC and the other underlying compilers possibly involved when building a package, a system image or any other GNU Guix output.

     $ guix build --target=aarch64-linux-gnu hello
     /gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12

     $ file /gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12/bin/hello
     /gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12/bin/hello: ELF
     64-bit LSB executable, ARM aarch64 ...

The major benefit of cross-compilation is that there are no performance penalty compared to emulation using QEMU.  There are however higher risks that some packages fail to cross-compile because fewer users are using this mechanism extensively.

Native Builds
=============

The commands that support impersonating a specific system have the --list-systems and --system options.

The --list-systems option lists all the supported systems that can be passed as an argument to --system.

     $ guix build --list-systems
     The available systems are:

        - x86_64-linux [current]
        - aarch64-linux
        - armhf-linux
        - i586-gnu
        - i686-linux
        - mips64el-linux
        - powerpc-linux
        - powerpc64le-linux
        - riscv64-linux

     $ guix build --system=i686-linux hello
     /gnu/store/cc0km35s8x2z4pmwkrqqjx46i8b1i3gm-hello-2.12

     $ file /gnu/store/cc0km35s8x2z4pmwkrqqjx46i8b1i3gm-hello-2.12/bin/hello
     /gnu/store/cc0km35s8x2z4pmwkrqqjx46i8b1i3gm-hello-2.12/bin/hello: ELF
     32-bit LSB executable, Intel 80386 ...

In the above example, the current system is X86_64-LINUX.  The HELLO package is however built for the I686-LINUX system.

This is possible because the I686 CPU instruction set is a subset of the X86_64, hence I686 targeting binaries can be run on X86_64.

Still in the context of the previous example, if picking the AARCH64-LINUX system and the guix build --system=aarch64-linux hello has to build some derivations, an extra step might be needed.

The AARCH64-LINUX targeting binaries cannot directly be run on a X86_64-LINUX system.  An emulation layer is requested.  The GNU Guix daemon can take advantage of the Linux kernel binfmt_misc (https://en.wikipedia.org/wiki/Binfmt_misc) mechanism for that.  In short, the Linux kernel can defer the execution of a binary targeting a foreign platform, here AARCH64-LINUX, to a userspace program, usually an emulator.

There is a service that registers QEMU as a backend for the binfmt_misc mechanism (see qemu-binfmt-service-type).  On Debian based foreign distributions, the alternative would be the qemu-user-static package.

If the binfmt_misc mechanism is not setup correctly, the building will fail this way:

     $ guix build --system=armhf-linux hello --check
     ...
      unsupported-platform /gnu/store/jjn969pijv7hff62025yxpfmc8zy0aq0-hello-2.12.drv aarch64-linux
     while setting up the build environment: a `aarch64-linux' is required to
     build `/gnu/store/jjn969pijv7hff62025yxpfmc8zy0aq0-hello-2.12.drv', but
     I am a `x86_64-linux'...

whereas, with the binfmt_misc mechanism correctly linked with QEMU, one can expect to see:

     $ guix build --system=armhf-linux hello --check
     /gnu/store/13xz4nghg39wpymivlwghy08yzj97hlj-hello-2.12

The main advantage of native building compared to cross-compiling, is that more packages are likely to build correctly.  However it comes at a price: compilation backed by QEMU is way slower than cross-compilation, because every instruction needs to be emulated.

The availability of substitutes for the architecture targeted by the --system option can mitigate this problem.  An other way to work around it is to install GNU Guix on a machine whose CPU supports the targeted instruction set, and set it up as an offload machine (see Daemon Offload Setup).

System Configuration
********************

Guix System supports a consistent whole-system configuration mechanism.  By that we mean that all aspects of the global system configuration---such as the available system services, timezone and locale settings, user accounts---are declared in a single place.  Such a system configuration can be instantiated---i.e., effected.

One of the advantages of putting all the system configuration under the control of Guix is that it supports transactional system upgrades, and makes it possible to roll back to a previous system instantiation, should something go wrong with the new one (see Features).  Another advantage is that it makes it easy to replicate the exact same configuration across different machines, or at different points in time, without having to resort to additional administration tools layered on top of the own tools of the system.

This section describes this mechanism.  First we focus on the system administrator's viewpoint---explaining how the system is configured and instantiated.  Then we show how this mechanism can be extended, for instance to support new system services.

Using the Configuration System
==============================

The operating system is configured by providing an operating-system declaration in a file that can then be passed to the guix system command (see Invoking guix system).  A simple setup, with the default Linux-Libre kernel, initial RAM disk, and a couple of system services added to those provided by default looks like this:

          [file os-config-bare-bones.texi not included]

The configuration is declarative and hopefully mostly self-describing. It is actually code in the Scheme programming language; the whole (operating-system ...) expression produces a record with a number of fields. Some of the fields defined above, such as host-name and bootloader, are mandatory. Others, such as packages and services, can be omitted, in which case they get a default value.  See operating-system Reference, for details about all the available fields.

Below we discuss the effect of some of the most important fields, and how to instantiate the operating system using guix system.

     Intimidated by the Scheme language or curious about it?  The Cookbook has a short section to get started that explains the fundamentals, which you will find helpful when hacking your configuration.  See A Scheme Crash Course (GNU Guix Cookbook).

Bootloader
----------

The bootloader field describes the method that will be used to boot your system.  Machines based on Intel processors can boot in ``legacy'' BIOS mode, as in the example above.  However, more recent machines rely instead on the Unified Extensible Firmware Interface (UEFI) to boot.  In that case, the bootloader field should contain something along these lines:

     (bootloader-configuration
       (bootloader grub-efi-bootloader)
       (targets '("/boot/efi")))

See Bootloader Configuration, for more information on the available configuration options.

Globally-Visible Packages
-------------------------

The packages field lists packages that will be globally visible on the system, for all user accounts---i.e., in every user's PATH environment variable---in addition to the per-user profiles (see Invoking guix package).  The %base-packages variable provides all the tools one would expect for basic user and administrator tasks---including the GNU Core Utilities, the GNU Networking Utilities, the mg lightweight text editor, find, grep, etc.  The example above adds GNU Screen to those, taken from the (gnu packages screen) module (see Package Modules).  The (list package output) syntax can be used to add a specific output of a package:

     (use-modules (gnu packages))
     (use-modules (gnu packages dns))

     (operating-system
       ;; ...
       (packages (cons (list isc-bind "utils")
                       %base-packages)))

Referring to packages by variable name, like isc-bind above, has the advantage of being unambiguous; it also allows typos and such to be diagnosed right away as ``unbound variables''.  The downside is that one needs to know which module defines which package, and to augment the use-package-modules line accordingly.  To avoid that, one can use the specification->package procedure of the (gnu packages) module, which returns the best package for a given name or name and version:

     (use-modules (gnu packages))

     (operating-system
       ;; ...
       (packages (append (map specification->package
                              '("tcpdump" "htop" "gnupg@2.0"))
                         %base-packages)))

When a package has more than one output it can be a challenge to refer to a specific output instead of just to the standard out output.  For these situations one can use the specification->package+output procedure from the (gnu packages) module.  For example:

     (use-modules (gnu packages))

     (operating-system
       ;; ...
       (packages (append (map specification->package+output
                              '("nss-certs" "git" "git:send-email"))
                         %base-packages)))

System Services
---------------

The services field lists system services to be made available when the system starts (see Services). The operating-system declaration above specifies that, in addition to the basic services, we want the OpenSSH secure shell daemon listening on port 2222 (see openssh-service-type).  Under the hood, openssh-service-type arranges so that sshd is started with the right command-line options, possibly with supporting configuration files generated as needed (see Defining Services).

Occasionally, instead of using the base services as is, you will want to customize them.  To do this, use modify-services (see modify-services) to modify the list.

 For example, suppose you want to modify guix-daemon and Mingetty (the console log-in) in the %base-services list (see %base-services).  To do that, you can write the following in your operating system declaration:

     (define %my-services
       ;; My very own list of services.
       (modify-services %base-services
         (guix-service-type config =>
                            (guix-configuration
                             (inherit config)
                             ;; Fetch substitutes from example.org.
                             (substitute-urls
                               (list "https://example.org/guix"
                                     "https://ci.guix.gnu.org"))))
         (mingetty-service-type config =>
                                (mingetty-configuration
                                 (inherit config)
                                 ;; Automatically log in as "guest".
                                 (auto-login "guest")))))

     (operating-system
       ;; ...
       (services %my-services))

This changes the configuration---i.e., the service parameters---of the guix-service-type instance, and that of all the mingetty-service-type instances in the %base-services list (see see the cookbook for how to auto-login one user to a specific TTY (GNU Guix Cookbook))). Observe how this is accomplished: first, we arrange for the original configuration to be bound to the identifier config in the BODY, and then we write the BODY so that it evaluates to the desired configuration.  In particular, notice how we use inherit to create a new configuration which has the same values as the old configuration, but with a few modifications.

The configuration for a typical ``desktop'' usage, with an encrypted root partition, a swap file on the root partition, the X11 display server, GNOME and Xfce (users can choose which of these desktop environments to use at the log-in screen by pressing F1), network management, power management, and more, would look like this:

          [file os-config-desktop.texi not included]

A graphical system with a choice of lightweight window managers instead of full-blown desktop environments would look like this:

          [file os-config-lightweight-desktop.texi not included]

This example refers to the /boot/efi file system by its UUID, 1234-ABCD.  Replace this UUID with the right UUID on your system, as returned by the blkid command.

See Desktop Services, for the exact list of services provided by %desktop-services.  See X.509 Certificates, for background information about the nss-certs package that is used here.

Again, %desktop-services is just a list of service objects.  If you want to remove services from there, you can do so using the procedures for list filtering (see SRFI-1 Filtering and Partitioning (GNU Guile Reference Manual)).  For instance, the following expression returns a list that contains all the services in %desktop-services minus the Avahi service:

     (remove (lambda (service)
               (eq? (service-kind service) avahi-service-type))
             %desktop-services)

Alternatively, the modify-services macro can be used:

     (modify-services %desktop-services
       (delete avahi-service-type))

Instantiating the System
------------------------

Assuming the operating-system declaration is stored in the my-system-config.scm file, the guix system reconfigure my-system-config.scm command instantiates that configuration, and makes it the default GRUB boot entry (see Invoking guix system).

     We recommend that you keep this my-system-config.scm file safe and under version control to easily track changes to your configuration.

The normal way to change the system configuration is by updating this file and re-running guix system reconfigure.  One should never have to touch files in /etc or to run commands that modify the system state such as useradd or grub-install.  In fact, you must avoid that since that would not only void your warranty but also prevent you from rolling back to previous versions of your system, should you ever need to.

Speaking of roll-back, each time you run guix system reconfigure, a new generation of the system is created---without modifying or deleting previous generations.  Old system generations get an entry in the bootloader boot menu, allowing you to boot them in case something went wrong with the latest generation.  Reassuring, no?  The guix system list-generations command lists the system generations available on disk.  It is also possible to roll back the system via the commands guix system roll-back and guix system switch-generation.

Although the guix system reconfigure command will not modify previous generations, you must take care when the current generation is not the latest (e.g., after invoking guix system roll-back), since the operation might overwrite a later generation (see Invoking guix system).

The Programming Interface
-------------------------

At the Scheme level, the bulk of an operating-system declaration is instantiated with the following monadic procedure (see The Store Monad):

 -- Monadic Procedure: operating-system-derivation os
     Return a derivation that builds OS, an operating-system object (see Derivations).

     The output of the derivation is a single directory that refers to all the packages, configuration files, and other supporting files needed to instantiate OS.

This procedure is provided by the (gnu system) module.  Along with (gnu services) (see Services), this module contains the guts of Guix System.  Make sure to visit it!

operating-system Reference
==========================

This section summarizes all the options available in operating-system declarations (see Using the Configuration System).

 -- Data Type: operating-system
     This is the data type representing an operating system configuration. By that, we mean all the global system configuration, not per-user configuration (see Using the Configuration System).

     kernel (default: linux-libre)
          The package object of the operating system kernel to use (Currently only the Linux-libre kernel is fully supported. Using GNU mach with the GNU Hurd is experimental and only available when building a virtual machine disk image.).

     hurd (default: #f)
          The package object of the Hurd to be started by the kernel.  When this field is set, produce a GNU/Hurd operating system.  In that case, kernel must also be set to the gnumach package---the microkernel the Hurd runs on.

               This feature is experimental and only supported for disk images.

     kernel-loadable-modules (default: '())
          A list of objects (usually packages) to collect loadable kernel modules from--e.g. (list ddcci-driver-linux).

     kernel-arguments (default: %default-kernel-arguments)
          List of strings or gexps representing additional arguments to pass on the command-line of the kernel---e.g., ("console=ttyS0").

     bootloader
          The system bootloader configuration object.  See Bootloader Configuration.

     label
          This is the label (a string) as it appears in the bootloader's menu entry. The default label includes the kernel name and version.

     keyboard-layout (default: #f)
          This field specifies the keyboard layout to use in the console.  It can be either #f, in which case the default keyboard layout is used (usually US English), or a <keyboard-layout> record. See Keyboard Layout, for more information.

          This keyboard layout is in effect as soon as the kernel has booted.  For instance, it is the keyboard layout in effect when you type a passphrase if your root file system is on a luks-device-mapping mapped device (see Mapped Devices).

               This does not specify the keyboard layout used by the bootloader, nor that used by the graphical display server.  See Bootloader Configuration, for information on how to specify the bootloader's keyboard layout.  See X Window, for information on how to specify the keyboard layout used by the X Window System.

     initrd-modules (default: %base-initrd-modules)
          The list of Linux kernel modules that need to be available in the initial RAM disk.  See Initial RAM Disk.

     initrd (default: base-initrd)
          A procedure that returns an initial RAM disk for the Linux kernel.  This field is provided to support low-level customization and should rarely be needed for casual use.  See Initial RAM Disk.

     firmware (default: %base-firmware)
          List of firmware packages loadable by the operating system kernel.

          The default includes firmware needed for Atheros- and Broadcom-based WiFi devices (Linux-libre modules ath9k and b43-open, respectively).  See Hardware Considerations, for more info on supported hardware.

     host-name
          The host name.

     mapped-devices (default: '())
          A list of mapped devices.  See Mapped Devices.

     file-systems
          A list of file systems.  See File Systems.

     swap-devices (default: '())
          A list of swap spaces.  See Swap Space.

     users (default: %base-user-accounts)
     groups (default: %base-groups)
          List of user accounts and groups.  See User Accounts.

          If the users list lacks a user account with UID 0, a ``root'' account with UID 0 is automatically added.

     skeletons (default: (default-skeletons))
          A list of target file name/file-like object tuples (see file-like objects).  These are the skeleton files that will be added to the home directory of newly-created user accounts.

          For instance, a valid value may look like this:

               `((".bashrc" ,(plain-file "bashrc" "echo Hello\n"))
                 (".guile" ,(plain-file "guile"
                                        "(use-modules (ice-9 readline))
                                         (activate-readline)")))

     issue (default: %default-issue)
          A string denoting the contents of the /etc/issue file, which is displayed when users log in on a text console.

     packages (default: %base-packages)
          A list of packages to be installed in the global profile, which is accessible at /run/current-system/profile.  Each element is either a package variable or a package/output tuple.  Here's a simple example of both:

               (cons* git                     ; the default "out" output
                      (list git "send-email") ; another output of git
                      %base-packages)         ; the default set

          The default set includes core utilities and it is good practice to install non-core utilities in user profiles (see Invoking guix package).

     timezone (default: "Etc/UTC")
          A timezone identifying string---e.g., "Europe/Paris".

          You can run the tzselect command to find out which timezone string corresponds to your region.  Choosing an invalid timezone name causes guix system to fail.

     locale (default: "en_US.utf8")
          The name of the default locale (see Locale Names (The GNU C Library Reference Manual)).  See Locales, for more information.

     locale-definitions (default: %default-locale-definitions)
          The list of locale definitions to be compiled and that may be used at run time.  See Locales.

     locale-libcs (default: (list GLIBC))
          The list of GNU libc packages whose locale data and tools are used to build the locale definitions.  See Locales, for compatibility considerations that justify this option.

     name-service-switch (default: %default-nss)
          Configuration of the libc name service switch (NSS)---a <name-service-switch> object.  See Name Service Switch, for details.

     services (default: %base-services)
          A list of service objects denoting system services.  See Services.

     essential-services (default: ...)
          The list of ``essential services''---i.e., things like instances of system-service-type (see Service Reference) and host-name-service-type, which are derived from the operating system definition itself.  As a user you should never need to touch this field.

     pam-services (default: (base-pam-services))
          Linux pluggable authentication module (PAM) services.

     setuid-programs (default: %setuid-programs)
          List of <setuid-program>.  See Setuid Programs, for more information.

     sudoers-file (default: %sudoers-specification)
          The contents of the /etc/sudoers file as a file-like object (see local-file and plain-file).

          This file specifies which users can use the sudo command, what they are allowed to do, and what privileges they may gain.  The default is that only root and members of the wheel group may use sudo.

      -- Macro: this-operating-system
          When used in the lexical scope of an operating system field definition, this identifier resolves to the operating system being defined.

          The example below shows how to refer to the operating system being defined in the definition of the label field:

               (use-modules (gnu) (guix))

               (operating-system
                 ;; ...
                 (label (package-full-name
                         (operating-system-kernel this-operating-system))))

          It is an error to refer to this-operating-system outside an operating system definition.

File Systems
============

The list of file systems to be mounted is specified in the file-systems field of the operating system declaration (see Using the Configuration System).  Each file system is declared using the file-system form, like this:

     (file-system
       (mount-point "/home")
       (device "/dev/sda3")
       (type "ext4"))

As usual, some of the fields are mandatory---those shown in the example above---while others can be omitted.  These are described below.

 -- Data Type: file-system
     Objects of this type represent file systems to be mounted.  They contain the following members:

     type
          This is a string specifying the type of the file system---e.g., "ext4".

     mount-point
          This designates the place where the file system is to be mounted.

     device
          This names the ``source'' of the file system.  It can be one of three things: a file system label, a file system UUID, or the name of a /dev node.  Labels and UUIDs offer a way to refer to file systems without having to hard-code their actual device name (Note that, while it is tempting to use /dev/disk/by-uuid and similar device names to achieve the same result, this is not recommended: These special device nodes are created by the udev daemon and may be unavailable at the time the device is mounted.).

          File system labels are created using the file-system-label procedure, UUIDs are created using uuid, and /dev nodes are plain strings.  Here's an example of a file system referred to by its label, as shown by the e2label command:

               (file-system
                 (mount-point "/home")
                 (type "ext4")
                 (device (file-system-label "my-home")))

          UUIDs are converted from their string representation (as shown by the tune2fs -l command) using the uuid form (The uuid form expects 16-byte UUIDs as defined in RFC 4122 (https://tools.ietf.org/html/rfc4122).  This is the form of UUID used by the ext2 family of file systems and others, but it is different from ``UUIDs'' found in FAT file systems, for instance.), like this:

               (file-system
                 (mount-point "/home")
                 (type "ext4")
                 (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))

          When the source of a file system is a mapped device (see Mapped Devices), its device field must refer to the mapped device name---e.g., "/dev/mapper/root-partition". This is required so that the system knows that mounting the file system depends on having the corresponding device mapping established.

     flags (default: '())
          This is a list of symbols denoting mount flags.  Recognized flags include read-only, bind-mount, no-dev (disallow access to special files), no-suid (ignore setuid and setgid bits), no-atime (do not update file access times), no-diratime (likewise for directories only), strict-atime (update file access time), lazy-time (only update time on the in-memory version of the file inode), no-exec (disallow program execution), and shared (make the mount shared). See Mount-Unmount-Remount (The GNU C Library Reference Manual), for more information on these flags.

     options (default: #f)
          This is either #f, or a string denoting mount options passed to the file system driver.  See Mount-Unmount-Remount (The GNU C Library Reference Manual), for details.

          Run man 8 mount for options for various file systems, but beware that what it lists as file-system-independent ``mount options'' are in fact flags, and belong in the flags field described above.

          The file-system-options->alist and alist->file-system-options procedures from (gnu system file-systems) can be used to convert file system options given as an association list to the string representation, and vice-versa.

     mount? (default: #t)
          This value indicates whether to automatically mount the file system when the system is brought up.  When set to #f, the file system gets an entry in /etc/fstab (read by the mount command) but is not automatically mounted.

     needed-for-boot? (default: #f)
          This Boolean value indicates whether the file system is needed when booting.  If that is true, then the file system is mounted when the initial RAM disk (initrd) is loaded.  This is always the case, for instance, for the root file system.

     check? (default: #t)
          This Boolean indicates whether the file system should be checked for errors before being mounted.  How and when this happens can be further adjusted with the following options.

     skip-check-if-clean? (default: #t)
          When true, this Boolean indicates that a file system check triggered by check? may exit early if the file system is marked as ``clean'', meaning that it was previously correctly unmounted and should not contain errors.

          Setting this to false will always force a full consistency check when check? is true.  This may take a very long time and is not recommended on healthy systems---in fact, it may reduce reliability!

          Conversely, some primitive file systems like fat do not keep track of clean shutdowns and will perform a full scan regardless of the value of this option.

     repair (default: 'preen)
          When check? finds errors, it can (try to) repair them and continue booting.  This option controls when and how to do so.

          If false, try not to modify the file system at all.  Checking certain file systems like jfs may still write to the device to replay the journal.  No repairs will be attempted.

          If #t, try to repair any errors found and assume ``yes'' to all questions.  This will fix the most errors, but may be risky.

          If 'preen, repair only errors that are safe to fix without human interaction.  What that means is left up to the developers of each file system and may be equivalent to ``none'' or ``all''.

     create-mount-point? (default: #f)
          When true, the mount point is created if it does not exist yet.

     mount-may-fail? (default: #f)
          When true, this indicates that mounting this file system can fail but that should not be considered an error.  This is useful in unusual cases; an example of this is efivarfs, a file system that can only be mounted on EFI/UEFI systems.

     dependencies (default: '())
          This is a list of <file-system> or <mapped-device> objects representing file systems that must be mounted or mapped devices that must be opened before (and unmounted or closed after) this one.

          As an example, consider a hierarchy of mounts: /sys/fs/cgroup is a dependency of /sys/fs/cgroup/cpu and /sys/fs/cgroup/memory.

          Another example is a file system that depends on a mapped device, for example for an encrypted partition (see Mapped Devices).

 -- Procedure: file-system-label str
     This procedure returns an opaque file system label from STR, a string:

          (file-system-label "home")
          => #<file-system-label "home">

     File system labels are used to refer to file systems by label rather than by device name.  See above for examples.

The (gnu system file-systems) exports the following useful variables.

 -- Variable: %base-file-systems
     These are essential file systems that are required on normal systems, such as %pseudo-terminal-file-system and %immutable-store (see below).  Operating system declarations should always contain at least these.

 -- Variable: %pseudo-terminal-file-system
     This is the file system to be mounted as /dev/pts.  It supports pseudo-terminals created via openpty and similar functions (see Pseudo-Terminals (The GNU C Library Reference Manual)).  Pseudo-terminals are used by terminal emulators such as xterm.

 -- Variable: %shared-memory-file-system
     This file system is mounted as /dev/shm and is used to support memory sharing across processes (see shm_open (The GNU C Library Reference Manual)).

 -- Variable: %immutable-store
     This file system performs a read-only ``bind mount'' of /gnu/store, making it read-only for all the users including root.  This prevents against accidental modification by software running as root or by system administrators.

     The daemon itself is still able to write to the store: it remounts it read-write in its own ``name space.''

 -- Variable: %binary-format-file-system
     The binfmt_misc file system, which allows handling of arbitrary executable file types to be delegated to user space.  This requires the binfmt.ko kernel module to be loaded.

 -- Variable: %fuse-control-file-system
     The fusectl file system, which allows unprivileged users to mount and unmount user-space FUSE file systems.  This requires the fuse.ko kernel module to be loaded.

The (gnu system uuid) module provides tools to deal with file system ``unique identifiers'' (UUIDs).

 -- Procedure: uuid str [type]
     Return an opaque UUID (unique identifier) object of the given TYPE (a symbol) by parsing STR (a string):

          (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")
          => #<<uuid> type: dce bv: ...>

          (uuid "1234-ABCD" 'fat)
          => #<<uuid> type: fat bv: ...>

     TYPE may be one of dce, iso9660, fat, ntfs, or one of the commonly found synonyms for these.

     UUIDs are another way to unambiguously refer to file systems in operating system configuration.  See the examples above.

Btrfs file system
-----------------

The Btrfs has special features, such as subvolumes, that merit being explained in more details.  The following section attempts to cover basic as well as complex uses of a Btrfs file system with the Guix System.

In its simplest usage, a Btrfs file system can be described, for example, by:

     (file-system
       (mount-point "/home")
       (type "btrfs")
       (device (file-system-label "my-home")))

The example below is more complex, as it makes use of a Btrfs subvolume, named rootfs.  The parent Btrfs file system is labeled my-btrfs-pool, and is located on an encrypted device (hence the dependency on mapped-devices):

     (file-system
       (device (file-system-label "my-btrfs-pool"))
       (mount-point "/")
       (type "btrfs")
       (options "subvol=rootfs")
       (dependencies mapped-devices))

Some bootloaders, for example GRUB, only mount a Btrfs partition at its top level during the early boot, and rely on their configuration to refer to the correct subvolume path within that top level.  The bootloaders operating in this way typically produce their configuration on a running system where the Btrfs partitions are already mounted and where the subvolume information is readily available.  As an example, grub-mkconfig, the configuration generator command shipped with GRUB, reads /proc/self/mountinfo to determine the top-level path of a subvolume.

The Guix System produces a bootloader configuration using the operating system configuration as its sole input; it is therefore necessary to extract the subvolume name on which /gnu/store lives (if any) from that operating system configuration.  To better illustrate, consider a subvolume named 'rootfs' which contains the root file system data.  In such situation, the GRUB bootloader would only see the top level of the root Btrfs partition, e.g.:

     /                   (top level)
     ├── rootfs          (subvolume directory)
         ├── gnu         (normal directory)
             ├── store   (normal directory)
     [...]

Thus, the subvolume name must be prepended to the /gnu/store path of the kernel, initrd binaries and any other files referred to in the GRUB configuration that must be found during the early boot.

The next example shows a nested hierarchy of subvolumes and directories:

     /                   (top level)
     ├── rootfs          (subvolume)
         ├── gnu         (normal directory)
             ├── store   (subvolume)
     [...]

This scenario would work without mounting the 'store' subvolume. Mounting 'rootfs' is sufficient, since the subvolume name matches its intended mount point in the file system hierarchy.  Alternatively, the 'store' subvolume could be referred to by setting the subvol option to either /rootfs/gnu/store or rootfs/gnu/store.

Finally, a more contrived example of nested subvolumes:

     /                           (top level)
     ├── root-snapshots          (subvolume)
         ├── root-current        (subvolume)
             ├── guix-store      (subvolume)
     [...]

Here, the 'guix-store' subvolume doesn't match its intended mount point, so it is necessary to mount it.  The subvolume must be fully specified, by passing its file name to the subvol option.  To illustrate, the 'guix-store' subvolume could be mounted on /gnu/store by using a file system declaration such as:

     (file-system
       (device (file-system-label "btrfs-pool-1"))
       (mount-point "/gnu/store")
       (type "btrfs")
       (options "subvol=root-snapshots/root-current/guix-store,\
     compress-force=zstd,space_cache=v2"))

Mapped Devices
==============

The Linux kernel has a notion of device mapping: a block device, such as a hard disk partition, can be mapped into another device, usually in /dev/mapper/, with additional processing over the data that flows through it (Note that the GNU Hurd makes no difference between the concept of a ``mapped device'' and that of a file system: both boil down to translating input/output operations made on a file to operations on its backing store.  Thus, the Hurd implements mapped devices, like file systems, using the generic translator mechanism (see Translators (The GNU Hurd Reference Manual)).).  A typical example is encryption device mapping: all writes to the mapped device are encrypted, and all reads are deciphered, transparently. Guix extends this notion by considering any device or set of devices that are transformed in some way to create a new device; for instance, RAID devices are obtained by assembling several other devices, such as hard disks or partitions, into a new one that behaves as one partition.

Mapped devices are declared using the mapped-device form, defined as follows; for examples, see below.

 -- Data Type: mapped-device
     Objects of this type represent device mappings that will be made when the system boots up.

     source
          This is either a string specifying the name of the block device to be mapped, such as "/dev/sda3", or a list of such strings when several devices need to be assembled for creating a new one.  In case of LVM this is a string specifying name of the volume group to be mapped.

     target
          This string specifies the name of the resulting mapped device.  For kernel mappers such as encrypted devices of type luks-device-mapping, specifying "my-partition" leads to the creation of the "/dev/mapper/my-partition" device. For RAID devices of type raid-device-mapping, the full device name such as "/dev/md0" needs to be given. LVM logical volumes of type lvm-device-mapping need to be specified as "VGNAME-LVNAME".

     targets
          This list of strings specifies names of the resulting mapped devices in case there are several.  The format is identical to TARGET.

     type
          This must be a mapped-device-kind object, which specifies how SOURCE is mapped to TARGET.

 -- Variable: luks-device-mapping
     This defines LUKS block device encryption using the cryptsetup command from the package with the same name.  It relies on the dm-crypt Linux kernel module.

 -- Procedure: luks-device-mapping-with-options [#:key-file]
     Return a luks-device-mapping object, which defines LUKS block device encryption using the cryptsetup command from the package with the same name.  It relies on the dm-crypt Linux kernel module.

     If key-file is provided, unlocking is first attempted using that key file.  This has an advantage of not requiring a password entry, so it can be used (for example) to unlock RAID arrays automatically on boot.  If key file unlock fails, password unlock is attempted as well. Key file is not stored in the store and needs to be available at the given location at the time of the unlock attempt.

          ;; Following definition would be equivalent to running:
          ;;   cryptsetup open --key-file /crypto.key /dev/sdb1 data
          (mapped-device
           (source "/dev/sdb1)
           (target "data)
           (type (luks-device-mapping-with-options
                  #:key-file "/crypto.key")))

 -- Variable: raid-device-mapping
     This defines a RAID device, which is assembled using the mdadm command from the package with the same name.  It requires a Linux kernel module for the appropriate RAID level to be loaded, such as raid456 for RAID-4, RAID-5 or RAID-6, or raid10 for RAID-10.

 -- Variable: lvm-device-mapping
     This defines one or more logical volumes for the Linux Logical Volume Manager (LVM) (https://www.sourceware.org/lvm2/). The volume group is activated by the vgchange command from the lvm2 package.

The following example specifies a mapping from /dev/sda3 to /dev/mapper/home using LUKS---the Linux Unified Key Setup (https://gitlab.com/cryptsetup/cryptsetup), a standard mechanism for disk encryption. The /dev/mapper/home device can then be used as the device of a file-system declaration (see File Systems).

     (mapped-device
       (source "/dev/sda3")
       (target "home")
       (type luks-device-mapping))

Alternatively, to become independent of device numbering, one may obtain the LUKS UUID (unique identifier) of the source device by a command like:

     cryptsetup luksUUID /dev/sda3

and use it as follows:

     (mapped-device
       (source (uuid "cb67fc72-0d54-4c88-9d4b-b225f30b0f44"))
       (target "home")
       (type luks-device-mapping))

It is also desirable to encrypt swap space, since swap space may contain sensitive data.  One way to accomplish that is to use a swap file in a file system on a device mapped via LUKS encryption.  In this way, the swap file is encrypted because the entire device is encrypted. See Swap Space, or see Disk Partitioning, for an example.

A RAID device formed of the partitions /dev/sda1 and /dev/sdb1 may be declared as follows:

     (mapped-device
       (source (list "/dev/sda1" "/dev/sdb1"))
       (target "/dev/md0")
       (type raid-device-mapping))

The /dev/md0 device can then be used as the device of a file-system declaration (see File Systems). Note that the RAID level need not be given; it is chosen during the initial creation and formatting of the RAID device and is determined automatically later.

LVM logical volumes ``alpha'' and ``beta'' from volume group ``vg0'' can be declared as follows:

     (mapped-device
       (source "vg0")
       (targets (list "vg0-alpha" "vg0-beta"))
       (type lvm-device-mapping))

Devices /dev/mapper/vg0-alpha and /dev/mapper/vg0-beta can then be used as the device of a file-system declaration (see File Systems).

Swap Space
==========

Swap space, as it is commonly called, is a disk area specifically designated for paging: the process in charge of memory management (the Linux kernel or Hurd's default pager) can decide that some memory pages stored in RAM which belong to a running program but are unused should be stored on disk instead.  It unloads those from the RAM, freeing up precious fast memory, and writes them to the swap space.  If the program tries to access that very page, the memory management process loads it back into memory for the program to use.

A common misconception about swap is that it is only useful when small amounts of RAM are available to the system.  However, it should be noted that kernels often use all available RAM for disk access caching to make I/O faster, and thus paging out unused portions of program memory will expand the RAM available for such caching.

For a more detailed description of how memory is managed from the viewpoint of a monolithic kernel, see Memory Concepts (The GNU C Library Reference Manual).

The Linux kernel has support for swap partitions and swap files: the former uses a whole disk partition for paging, whereas the second uses a file on a file system for that (the file system driver needs to support it).  On a comparable setup, both have the same performance, so one should consider ease of use when deciding between them.  Partitions are ``simpler'' and do not need file system support, but need to be allocated at disk formatting time (logical volumes notwithstanding), whereas files can be allocated and deallocated at any time.

Swap space is also required to put the system into hibernation (also called suspend to disk), whereby memory is dumped to swap before shutdown so it can be restored when the machine is eventually restarted.  Hibernation uses at most half the size of the RAM in the configured swap space.  The Linux kernel needs to know about the swap space to be used to resume from hibernation on boot (via a kernel argument).  When using a swap file, its offset in the device holding it also needs to be given to the kernel; that value has to be updated if the file is initialized again as swap---e.g., because its size was changed.

Note that swap space is not zeroed on shutdown, so sensitive data (such as passwords) may linger on it if it was paged out.  As such, you should consider having your swap reside on an encrypted device (see Mapped Devices).

 -- Data Type: swap-space
     Objects of this type represent swap spaces.  They contain the following members:

     target
          The device or file to use, either a UUID, a file-system-label or a string, as in the definition of a file-system (see File Systems).

     dependencies (default: '())
          A list of file-system or mapped-device objects, upon which the availability of the space depends.  Note that just like for file-system objects, dependencies which are needed for boot and mounted in early userspace are not managed by the Shepherd, and so automatically filtered out for you.

     priority (default: #f)
          Only supported by the Linux kernel.  Either #f to disable swap priority, or an integer between 0 and 32767.  The kernel will first use swap spaces of higher priority when paging, and use same priority spaces on a round-robin basis.  The kernel will use swap spaces without a set priority after prioritized spaces, and in the order that they appeared in (not round-robin).

     discard? (default: #f)
          Only supported by the Linux kernel.  When true, the kernel will notify the disk controller of discarded pages, for example with the TRIM operation on Solid State Drives.

Here are some examples:

     (swap-space (target (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))

Use the swap partition with the given UUID.  You can learn the UUID of a Linux swap partition by running swaplabel DEVICE, where DEVICE is the /dev file name of that partition.

     (swap-space
       (target (file-system-label "swap"))
       (dependencies mapped-devices))

Use the partition with label swap, which can be found after all the MAPPED-DEVICES mapped devices have been opened.  Again, the swaplabel command allows you to view and change the label of a Linux swap partition.

Here's a more involved example with the corresponding file-systems part of an operating-system declaration.

     (file-systems
       (list (file-system
               (device (file-system-label "root"))
               (mount-point "/")
               (type "ext4"))
             (file-system
               (device (file-system-label "btrfs"))
               (mount-point "/btrfs")
               (type "btrfs"))))

     (swap-devices
       (list
         (swap-space
           (target "/btrfs/swapfile")
           (dependencies (filter (file-system-mount-point-predicate "/btrfs")
                                 file-systems)))))

Use the file /btrfs/swapfile as swap space, which depends on the file system mounted at /btrfs.  Note how we use Guile's filter to select the file system in an elegant fashion!

     (swap-devices
       (list
         (swap-space
           (target "/dev/mapper/my-swap")
           (dependencies mapped-devices))))

     (kernel-arguments
       (cons* "resume=/dev/mapper/my-swap"
              %default-kernel-arguments))

The above snippet of an operating-system declaration enables the mapped device /dev/mapper/my-swap (which may be part of an encrypted device) as swap space, and tells the kernel to use it for hibernation via the resume kernel argument (see operating-system Reference, kernel-arguments).

     (swap-devices
       (list
         (swap-space
           (target "/swapfile")
           (dependencies (filter (file-system-mount-point-predicate "/")
                                 file-systems)))))

     (kernel-arguments
       (cons* "resume=/dev/sda3"        ;device that holds /swapfile
              "resume_offset=92514304"  ;offset of /swapfile on device
              %default-kernel-arguments))

This other snippet of operating-system enables the swap file /swapfile for hibernation by telling the kernel about the partition containing it (resume argument) and its offset on that partition (resume_offset argument).  The latter value can be found in the output of the command filefrag -e as the first number right under the physical_offset column header (the second command extracts its value directly):

     $ sudo filefrag -e /swapfile
     Filesystem type is: ef53
     File size of /swapfile is 2463842304 (601524 blocks of 4096 bytes)
      ext:     logical_offset:        physical_offset: length:   expected: flags:
        0:        0..    2047:   92514304..  92516351:   2048:
     ...
     $ sudo filefrag -e /swapfile | grep '^ *0:' | cut -d: -f3 | cut -d. -f1
        92514304

User Accounts
=============

User accounts and groups are entirely managed through the operating-system declaration.  They are specified with the user-account and user-group forms:

     (user-account
       (name "alice")
       (group "users")
       (supplementary-groups '("wheel"   ;allow use of sudo, etc.
                               "audio"   ;sound card
                               "video"   ;video devices such as webcams
                               "cdrom")) ;the good ol' CD-ROM
       (comment "Bob's sister"))

Here's a user account that uses a different shell and a custom home directory (the default would be "/home/bob"):

     (user-account
       (name "bob")
       (group "users")
       (comment "Alice's bro")
       (shell (file-append zsh "/bin/zsh"))
       (home-directory "/home/robert"))

When booting or upon completion of guix system reconfigure, the system ensures that only the user accounts and groups specified in the operating-system declaration exist, and with the specified properties.  Thus, account or group creations or modifications made by directly invoking commands such as useradd are lost upon reconfiguration or reboot.  This ensures that the system remains exactly as declared.

 -- Data Type: user-account
     Objects of this type represent user accounts.  The following members may be specified:

     name
          The name of the user account.

     group
          This is the name (a string) or identifier (a number) of the user group this account belongs to.

     supplementary-groups (default: '())
          Optionally, this can be defined as a list of group names that this account belongs to.

     uid (default: #f)
          This is the user ID for this account (a number), or #f.  In the latter case, a number is automatically chosen by the system when the account is created.

     comment (default: "")
          A comment about the account, such as the account owner's full name.

          Note that, for non-system accounts, users are free to change their real name as it appears in /etc/passwd using the chfn command.  When they do, their choice prevails over the system administrator's choice; reconfiguring does not change their name.

     home-directory
          This is the name of the home directory for the account.

     create-home-directory? (default: #t)
          Indicates whether the home directory of this account should be created if it does not exist yet.

     shell (default: Bash)
          This is a G-expression denoting the file name of a program to be used as the shell (see G-Expressions).  For example, you would refer to the Bash executable like this:

               (file-append bash "/bin/bash")

          ... and to the Zsh executable like that:

               (file-append zsh "/bin/zsh")

     system? (default: #f)
          This Boolean value indicates whether the account is a ``system'' account.  System accounts are sometimes treated specially; for instance, graphical login managers do not list them.

     password (default: #f)
          You would normally leave this field to #f, initialize user passwords as root with the passwd command, and then let users change it with passwd.  Passwords set with passwd are of course preserved across reboot and reconfiguration.

          If you do want to set an initial password for an account, then this field must contain the encrypted password, as a string.  You can use the crypt procedure for this purpose:

               (user-account
                 (name "charlie")
                 (group "users")

                 ;; Specify a SHA-512-hashed initial password.
                 (password (crypt "InitialPassword!" "$6$abc")))

               The hash of this initial password will be available in a file in /gnu/store, readable by all the users, so this method must be used with care.

          See Passphrase Storage (The GNU C Library Reference Manual), for more information on password encryption, and Encryption (GNU Guile Reference Manual), for information on Guile's crypt procedure.

User group declarations are even simpler:

     (user-group (name "students"))

 -- Data Type: user-group
     This type is for, well, user groups.  There are just a few fields:

     name
          The name of the group.

     id (default: #f)
          The group identifier (a number).  If #f, a new number is automatically allocated when the group is created.

     system? (default: #f)
          This Boolean value indicates whether the group is a ``system'' group. System groups have low numerical IDs.

     password (default: #f)
          What, user groups can have a password?  Well, apparently yes.  Unless #f, this field specifies the password of the group.

For convenience, a variable lists all the basic user groups one may expect:

 -- Variable: %base-groups
     This is the list of basic user groups that users and/or packages expect to be present on the system.  This includes groups such as ``root'', ``wheel'', and ``users'', as well as groups used to control access to specific devices such as ``audio'', ``disk'', and ``cdrom''.

 -- Variable: %base-user-accounts
     This is the list of basic system accounts that programs may expect to find on a GNU/Linux system, such as the ``nobody'' account.

     Note that the ``root'' account is not included here.  It is a special-case and is automatically added whether or not it is specified.

Keyboard Layout
===============

To specify what each key of your keyboard does, you need to tell the operating system what keyboard layout you want to use.  The default, when nothing is specified, is the US English QWERTY layout for 105-key PC keyboards. However, German speakers will usually prefer the German QWERTZ layout, French speakers will want the AZERTY layout, and so on; hackers might prefer Dvorak or bépo, and they might even want to further customize the effect of some of the keys.  This section explains how to get that done.

There are three components that will want to know about your keyboard layout:

  * The bootloader may want to know what keyboard layout you want to use (see keyboard-layout).  This is useful if you want, for instance, to make sure that you can type the passphrase of your encrypted root partition using the right layout.

  * The operating system kernel, Linux, will need that so that the console is properly configured (see keyboard-layout).

  * The graphical display server, usually Xorg, also has its own idea of the keyboard layout (see keyboard-layout).

Guix allows you to configure all three separately but, fortunately, it allows you to share the same keyboard layout for all three components.

Keyboard layouts are represented by records created by the keyboard-layout procedure of (gnu system keyboard).  Following the X Keyboard extension (XKB), each layout has four attributes: a name (often a language code such as ``fi'' for Finnish or ``jp'' for Japanese), an optional variant name, an optional keyboard model name, and a possibly empty list of additional options.  In most cases the layout name is all you care about.

 -- Procedure: keyboard-layout name [variant] [#:model] [#:options '()]
     Return a new keyboard layout with the given NAME and VARIANT.

     NAME must be a string such as "fr"; VARIANT must be a string such as "bepo" or "nodeadkeys".  See the xkeyboard-config package for valid options.

Here are a few examples:

     ;; The German QWERTZ layout.  Here we assume a standard
     ;; "pc105" keyboard model.
     (keyboard-layout "de")

     ;; The bépo variant of the French layout.
     (keyboard-layout "fr" "bepo")

     ;; The Catalan layout.
     (keyboard-layout "es" "cat")

     ;; Arabic layout with "Alt-Shift" to switch to US layout.
     (keyboard-layout "ar,us" #:options '("grp:alt_shift_toggle"))

     ;; The Latin American Spanish layout.  In addition, the
     ;; "Caps Lock" key is used as an additional "Ctrl" key,
     ;; and the "Menu" key is used as a "Compose" key to enter
     ;; accented letters.
     (keyboard-layout "latam"
                      #:options '("ctrl:nocaps" "compose:menu"))

     ;; The Russian layout for a ThinkPad keyboard.
     (keyboard-layout "ru" #:model "thinkpad")

     ;; The "US international" layout, which is the US layout plus
     ;; dead keys to enter accented characters.  This is for an
     ;; Apple MacBook keyboard.
     (keyboard-layout "us" "intl" #:model "macbook78")

See the share/X11/xkb directory of the xkeyboard-config package for a complete list of supported layouts, variants, and models.

Let's say you want your system to use the Turkish keyboard layout throughout your system---bootloader, console, and Xorg.  Here's what your system configuration would look like:

     ;; Using the Turkish layout for the bootloader, the console,
     ;; and for Xorg.

     (operating-system
       ;; ...
       (keyboard-layout (keyboard-layout "tr"))  ;for the console
       (bootloader (bootloader-configuration
                     (bootloader grub-efi-bootloader)
                     (targets '("/boot/efi"))
                     (keyboard-layout keyboard-layout))) ;for GRUB
       (services (cons (set-xorg-configuration
                         (xorg-configuration             ;for Xorg
                           (keyboard-layout keyboard-layout)))
                       %desktop-services)))

In the example above, for GRUB and for Xorg, we just refer to the keyboard-layout field defined above, but we could just as well refer to a different layout.  The set-xorg-configuration procedure communicates the desired Xorg configuration to the graphical log-in manager, by default GDM.

We've discussed how to specify the default keyboard layout of your system when it starts, but you can also adjust it at run time:

  * If you're using GNOME, its settings panel has a ``Region & Language'' entry where you can select one or more keyboard layouts.

  * Under Xorg, the setxkbmap command (from the same-named package) allows you to change the current layout.  For example, this is how you would change the layout to US Dvorak:

          setxkbmap us dvorak

  * The loadkeys command changes the keyboard layout in effect in the Linux console.  However, note that loadkeys does not use the XKB keyboard layout categorization described above.  The command below loads the French bépo layout:

          loadkeys fr-bepo

Locales
=======

A locale defines cultural conventions for a particular language and region of the world (see Locales (The GNU C Library Reference Manual)).  Each locale has a name that typically has the form LANGUAGE_TERRITORY.CODESET---e.g., fr_LU.utf8 designates the locale for the French language, with cultural conventions from Luxembourg, and using the UTF-8 encoding.

Usually, you will want to specify the default locale for the machine using the locale field of the operating-system declaration (see locale).

The selected locale is automatically added to the locale definitions known to the system if needed, with its codeset inferred from its name---e.g., bo_CN.utf8 will be assumed to use the UTF-8 codeset.  Additional locale definitions can be specified in the locale-definitions slot of operating-system---this is useful, for instance, if the codeset could not be inferred from the locale name.  The default set of locale definitions includes some widely used locales, but not all the available locales, in order to save space.

For instance, to add the North Frisian locale for Germany, the value of that field may be:

     (cons (locale-definition
             (name "fy_DE.utf8") (source "fy_DE"))
           %default-locale-definitions)

Likewise, to save space, one might want locale-definitions to list only the locales that are actually used, as in:

     (list (locale-definition
             (name "ja_JP.eucjp") (source "ja_JP")
             (charset "EUC-JP")))

The compiled locale definitions are available at /run/current-system/locale/X.Y, where X.Y is the libc version, which is the default location where the GNU libc provided by Guix looks for locale data.  This can be overridden using the LOCPATH environment variable (see LOCPATH and locale packages).

The locale-definition form is provided by the (gnu system locale) module.  Details are given below.

 -- Data Type: locale-definition
     This is the data type of a locale definition.

     name
          The name of the locale.  See Locale Names (The GNU C Library Reference Manual), for more information on locale names.

     source
          The name of the source for that locale.  This is typically the LANGUAGE_TERRITORY part of the locale name.

     charset (default: "UTF-8")
          The ``character set'' or ``code set'' for that locale, as defined by IANA (https://www.iana.org/assignments/character-sets).

 -- Variable: %default-locale-definitions
     A list of commonly used UTF-8 locales, used as the default value of the locale-definitions field of operating-system declarations.

     These locale definitions use the normalized codeset for the part that follows the dot in the name (see normalized codeset (The GNU C Library Reference Manual)).  So for instance it has uk_UA.utf8 but not, say, uk_UA.UTF-8.

Locale Data Compatibility Considerations
----------------------------------------

operating-system declarations provide a locale-libcs field to specify the GNU libc packages that are used to compile locale declarations (see operating-system Reference).  ``Why would I care?'', you may ask.  Well, it turns out that the binary format of locale data is occasionally incompatible from one libc version to another.

For instance, a program linked against libc version 2.21 is unable to read locale data produced with libc 2.22; worse, that program aborts instead of simply ignoring the incompatible locale data (Versions 2.23 and later of GNU libc will simply skip the incompatible locale data, which is already an improvement.). Similarly, a program linked against libc 2.22 can read most, but not all, of the locale data from libc 2.21 (specifically, LC_COLLATE data is incompatible); thus calls to setlocale may fail, but programs will not abort.

The ``problem'' with Guix is that users have a lot of freedom: They can choose whether and when to upgrade software in their profiles, and might be using a libc version different from the one the system administrator used to build the system-wide locale data.

Fortunately, unprivileged users can also install their own locale data and define GUIX_LOCPATH accordingly (see GUIX_LOCPATH and locale packages).

Still, it is best if the system-wide locale data at /run/current-system/locale is built for all the libc versions actually in use on the system, so that all the programs can access it---this is especially crucial on a multi-user system.  To do that, the administrator can specify several libc packages in the locale-libcs field of operating-system:

     (use-package-modules base)

     (operating-system
       ;; ...
       (locale-libcs (list glibc-2.21 (canonical-package glibc))))

This example would lead to a system containing locale definitions for both libc 2.21 and the current version of libc in /run/current-system/locale.

Services
========

An important part of preparing an operating-system declaration is listing system services and their configuration (see Using the Configuration System).  System services are typically daemons launched when the system boots, or other actions needed at that time---e.g., configuring network access.

Guix has a broad definition of ``service'' (see Service Composition), but many services are managed by the GNU Shepherd (see Shepherd Services).  On a running system, the herd command allows you to list the available services, show their status, start and stop them, or do other specific operations (see Jump Start (The GNU Shepherd Manual)).  For example:

     # herd status

The above command, run as root, lists the currently defined services.  The herd doc command shows a synopsis of the given service and its associated actions:

     # herd doc nscd
     Run libc's name service cache daemon (nscd).

     # herd doc nscd action invalidate
     invalidate: Invalidate the given cache--e.g., 'hosts' for host name lookups.

The start, stop, and restart sub-commands have the effect you would expect.  For instance, the commands below stop the nscd service and restart the Xorg display server:

     # herd stop nscd
     Service nscd has been stopped.
     # herd restart xorg-server
     Service xorg-server has been stopped.
     Service xorg-server has been started.

For some services, herd configuration returns the name of the service's configuration file, which can be handy to inspect its configuration:

     # herd configuration sshd
     /gnu/store/...-sshd_config

The following sections document the available services, starting with the core services, that may be used in an operating-system declaration.

Base Services
-------------

The (gnu services base) module provides definitions for the basic services that one expects from the system.  The services exported by this module are listed below.

 -- Variable: %base-services
     This variable contains a list of basic services (see Service Types and Services, for more information on service objects) one would expect from the system: a login service (mingetty) on each tty, syslogd, the libc name service cache daemon (nscd), the udev device manager, and more.

     This is the default value of the services field of operating-system declarations.  Usually, when customizing a system, you will want to append services to %base-services, like this:

          (append (list (service avahi-service-type)
                        (service openssh-service-type))
                  %base-services)

 -- Variable: special-files-service-type
     This is the service that sets up ``special files'' such as /bin/sh; an instance of it is part of %base-services.

     The value associated with special-files-service-type services must be a list of two-element lists where the first element is the ``special file'' and the second element is its target.  By default it is:

          `(("/bin/sh" ,(file-append bash "/bin/sh"))
            ("/usr/bin/env" ,(file-append coreutils "/bin/env")))

     If you want to add, say, /bin/bash to your system, you can change it to:

          `(("/bin/sh" ,(file-append bash "/bin/sh"))
            ("/usr/bin/env" ,(file-append coreutils "/bin/env"))
            ("/bin/bash" ,(file-append bash "/bin/bash")))

     Since this is part of %base-services, you can use modify-services to customize the set of special files (see modify-services).  But the simple way to add a special file is via the extra-special-file procedure (see below).

 -- Procedure: extra-special-file file target
     Use TARGET as the ``special file'' FILE.

     For example, adding the following lines to the services field of your operating system declaration leads to a /usr/bin/env symlink:

          (extra-special-file "/usr/bin/env"
                              (file-append coreutils "/bin/env"))

 -- Variable: host-name-service-type
     Type of the service that sets the system host name, whose value is a string. This service is included in operating-system by default (see essential-services).

 -- Variable: console-font-service-type
     Install the given fonts on the specified ttys (fonts are per virtual console on the kernel Linux).  The value of this service is a list of tty/font pairs.  The font can be the name of a font provided by the kbd package or any valid argument to setfont, as in this example:

          `(("tty1" . "LatGrkCyr-8x16")
            ("tty2" . ,(file-append
                          font-tamzen
                          "/share/kbd/consolefonts/TamzenForPowerline10x20.psf"))
            ("tty3" . ,(file-append
                          font-terminus
                          "/share/consolefonts/ter-132n"))) ; for HDPI

 -- Variable: hosts-service-type
     Type of the service that populates the entries for (/etc/hosts). This service type can be extended by passing it a list of host records.

     The example below shows how to add two entries to /etc/hosts:

          (simple-service 'add-extra-hosts
                          hosts-service-type
                          (list (host "192.0.2.1" "example.com"
                                      '("example.net" "example.org"))
                                (host "2001:db8::1" "example.com"
                                      '("example.net" "example.org"))))

          By default /etc/hosts comes with the following entries:

               127.0.0.1 localhost HOST-NAME
               ::1       localhost HOST-NAME

          For most setups this is what you want though if you find yourself in the situation where you want to change the default entries, you can do so in operating-system via modify-services (see modify-services).

          The following example shows how to unset HOST-NAME from being an alias of localhost.

               (operating-system
                 ;; ...

                 (essential-services
                  (modify-services
                    (operating-system-default-essential-services this-operating-system)
                    (hosts-service-type config => (list
                                                    (host "127.0.0.1" "localhost")
                                                    (host "::1"       "localhost"))))))

 -- Procedure: host ADDRESS CANONICAL-NAME [ALIASES]
     Return a new record for the host at ADDRESS with the given CANONICAL-NAME and possibly ALIASES.

     ADDRESS must be a string denoting a valid IPv4 or IPv6 address, and CANONICAL-NAME and the strings listed in ALIASES must be valid host names.

 -- Variable: login-service-type
     Type of the service that provides a console login service, whose value is a <login-configuration> object.

 -- Data Type: login-configuration
     Data type representing the configuration of login, which specifies the MOTD (message of the day), among other things.

     motd
          A file-like object containing the ``message of the day''.

     allow-empty-passwords? (default: #t)
          Allow empty passwords by default so that first-time users can log in when the 'root' account has just been created.

 -- Variable: mingetty-service-type
     Type of the service that runs Mingetty, an implementation of the virtual console log-in.  The value for this service is a <mingetty-configuration> object.

 -- Data Type: mingetty-configuration
     Data type representing the configuration of Mingetty, which specifies the tty to run, among other things.

     tty
          The name of the console this Mingetty runs on---e.g., "tty1".

     auto-login (default: #f)
          When true, this field must be a string denoting the user name under which the system automatically logs in.  When it is #f, a user name and password must be entered to log in.

     login-program (default: #f)
          This must be either #f, in which case the default log-in program is used (login from the Shadow tool suite), or a gexp denoting the name of the log-in program.

     login-pause? (default: #f)
          When set to #t in conjunction with AUTO-LOGIN, the user will have to press a key before the log-in shell is launched.

     clear-on-logout? (default: #t)
          When set to #t, the screen will be cleared after logout.

     mingetty (default: MINGETTY)
          The Mingetty package to use.

 -- Variable: agetty-service-type
     Type of the service that runs agetty, which implements virtual and serial console log-in.  The value for this service is a <agetty-configuration> object.

 -- Data Type: agetty-configuration
     Data type representing the configuration of agetty, which specifies the tty to run, among other things (See the agetty(8) man page for more information.).

     tty
          The name of the console this agetty runs on, as a string---e.g., "ttyS0".  This argument is optional, it will default to a reasonable default serial port used by the kernel Linux.

          For this, if there is a value for an option agetty.tty in the kernel command line, agetty will extract the device name of the serial port from it and use that.

          If not and if there is a value for an option console with a tty in the Linux command line, agetty will extract the device name of the serial port from it and use that.

          In both cases, agetty will leave the other serial device settings (baud rate etc.) alone---in the hope that Linux pinned them to the correct values.

     baud-rate (default: #f)
          A string containing a comma-separated list of one or more baud rates, in descending order.

     term (default: #f)
          A string containing the value used for the TERM environment variable.

     eight-bits? (default: #f)
          When #t, the tty is assumed to be 8-bit clean, and parity detection is disabled.

     auto-login (default: #f)
          When passed a login name, as a string, the specified user will be logged in automatically without prompting for their login name or password.

     no-reset? (default: #f)
          When #t, don't reset terminal cflags (control modes).

     host (default: #f)
          This accepts a string containing the ``login_host'', which will be written into the /var/run/utmpx file.

     remote? (default: #f)
          When set to #t in conjunction with HOST, this will add an -r fakehost option to the command line of the login program specified in LOGIN-PROGRAM.

     flow-control? (default: #f)
          When set to #t, enable hardware (RTS/CTS) flow control.

     no-issue? (default: #f)
          When set to #t, the contents of the /etc/issue file will not be displayed before presenting the login prompt.

     init-string (default: #f)
          This accepts a string that will be sent to the tty or modem before sending anything else.  It can be used to initialize a modem.

     no-clear? (default: #f)
          When set to #t, agetty will not clear the screen before showing the login prompt.

     login-program (default: (file-append shadow "/bin/login"))
          This must be either a gexp denoting the name of a log-in program, or unset, in which case the default value is the login from the Shadow tool suite.

     local-line (default: #f)
          Control the CLOCAL line flag.  This accepts one of three symbols as arguments, 'auto, 'always, or 'never.  If #f, the default value chosen by agetty is 'auto.

     extract-baud? (default: #f)
          When set to #t, instruct agetty to try to extract the baud rate from the status messages produced by certain types of modems.

     skip-login? (default: #f)
          When set to #t, do not prompt the user for a login name.  This can be used with LOGIN-PROGRAM field to use non-standard login systems.

     no-newline? (default: #f)
          When set to #t, do not print a newline before printing the /etc/issue file.

     login-options (default: #f)
          This option accepts a string containing options that are passed to the login program.  When used with the LOGIN-PROGRAM, be aware that a malicious user could try to enter a login name containing embedded options that could be parsed by the login program.

     login-pause (default: #f)
          When set to #t, wait for any key before showing the login prompt. This can be used in conjunction with AUTO-LOGIN to save memory by lazily spawning shells.

     chroot (default: #f)
          Change root to the specified directory.  This option accepts a directory path as a string.

     hangup? (default: #f)
          Use the Linux system call vhangup to do a virtual hangup of the specified terminal.

     keep-baud? (default: #f)
          When set to #t, try to keep the existing baud rate.  The baud rates from BAUD-RATE are used when agetty receives a BREAK character.

     timeout (default: #f)
          When set to an integer value, terminate if no user name could be read within TIMEOUT seconds.

     detect-case? (default: #f)
          When set to #t, turn on support for detecting an uppercase-only terminal.  This setting will detect a login name containing only uppercase letters as indicating an uppercase-only terminal and turn on some upper-to-lower case conversions.  Note that this will not support Unicode characters.

     wait-cr? (default: #f)
          When set to #t, wait for the user or modem to send a carriage-return or linefeed character before displaying /etc/issue or login prompt.  This is typically used with the INIT-STRING option.

     no-hints? (default: #f)
          When set to #t, do not print hints about Num, Caps, and Scroll locks.

     no-hostname? (default: #f)
          By default, the hostname is printed.  When this option is set to #t, no hostname will be shown at all.

     long-hostname? (default: #f)
          By default, the hostname is only printed until the first dot.  When this option is set to #t, the fully qualified hostname by gethostname or getaddrinfo is shown.

     erase-characters (default: #f)
          This option accepts a string of additional characters that should be interpreted as backspace when the user types their login name.

     kill-characters (default: #f)
          This option accepts a string that should be interpreted to mean ``ignore all previous characters'' (also called a ``kill'' character) when the user types their login name.

     chdir (default: #f)
          This option accepts, as a string, a directory path that will be changed to before login.

     delay (default: #f)
          This options accepts, as an integer, the number of seconds to sleep before opening the tty and displaying the login prompt.

     nice (default: #f)
          This option accepts, as an integer, the nice value with which to run the login program.

     extra-options (default: '())
          This option provides an ``escape hatch'' for the user to provide arbitrary command-line arguments to agetty as a list of strings.

     shepherd-requirement (default: '())
          The option can be used to provides extra shepherd requirements (for example 'syslogd) to the respective 'term-* shepherd service.

 -- Variable: kmscon-service-type
     Type of the service that runs kmscon (https://www.freedesktop.org/wiki/Software/kmscon), which implements virtual console log-in.  The value for this service is a <kmscon-configuration> object.

 -- Data Type: kmscon-configuration
     Data type representing the configuration of Kmscon, which specifies the tty to run, among other things.

     virtual-terminal
          The name of the console this Kmscon runs on---e.g., "tty1".

     login-program (default: #~(string-append #$shadow "/bin/login"))
          A gexp denoting the name of the log-in program.  The default log-in program is login from the Shadow tool suite.

     login-arguments (default: '("-p"))
          A list of arguments to pass to login.

     auto-login (default: #f)
          When passed a login name, as a string, the specified user will be logged in automatically without prompting for their login name or password.

     hardware-acceleration? (default: #f)
          Whether to use hardware acceleration.

     font-engine (default: "pango")
          Font engine used in Kmscon.

     font-size (default: 12)
          Font size used in Kmscon.

     keyboard-layout (default: #f)
          If this is #f, Kmscon uses the default keyboard layout---usually US English (``qwerty'') for a 105-key PC keyboard.

          Otherwise this must be a keyboard-layout object specifying the keyboard layout.  See Keyboard Layout, for more information on how to specify the keyboard layout.

     kmscon (default: KMSCON)
          The Kmscon package to use.

 -- Variable: nscd-service-type
     Type of the service that runs the libc nscd (name service cache daemon), whose value is an <nscd-configuration> object.

     For convenience, the Shepherd service for nscd provides the following actions:

     invalidate
          This invalidate the given cache.  For instance, running:

               herd invalidate nscd hosts

          invalidates the host name lookup cache of nscd.

     statistics
          Running herd statistics nscd displays information about nscd usage and caches.

 -- Data Type: nscd-configuration
     Data type representing the nscd (name service cache daemon) configuration.

     name-services (default: '())
          List of packages denoting name services that must be visible to the nscd---e.g., (list NSS-MDNS).

     glibc (default: GLIBC)
          Package object denoting the GNU C Library providing the nscd command.

     log-file (default: "/var/log/nscd.log")
          Name of the nscd log file.  This is where debugging output goes when debug-level is strictly positive.

     debug-level (default: 0)
          Integer denoting the debugging levels.  Higher numbers mean that more debugging output is logged.

     caches (default: %nscd-default-caches)
          List of <nscd-cache> objects denoting things to be cached; see below.

 -- Data Type: nscd-cache
     Data type representing a cache database of nscd and its parameters.

     database
          This is a symbol representing the name of the database to be cached. Valid values are passwd, group, hosts, and services, which designate the corresponding NSS database (see NSS Basics (The GNU C Library Reference Manual)).

     positive-time-to-live
     negative-time-to-live (default: 20)
          A number representing the number of seconds during which a positive or negative lookup result remains in cache.

     check-files? (default: #t)
          Whether to check for updates of the files corresponding to DATABASE.

          For instance, when DATABASE is hosts, setting this flag instructs nscd to check for updates in /etc/hosts and to take them into account.

     persistent? (default: #t)
          Whether the cache should be stored persistently on disk.

     shared? (default: #t)
          Whether the cache should be shared among users.

     max-database-size (default: 32 MiB)
          Maximum size in bytes of the database cache.

 -- Variable: %nscd-default-caches
     List of <nscd-cache> objects used by default by nscd-configuration (see above).

     It enables persistent and aggressive caching of service and host name lookups.  The latter provides better host name lookup performance, resilience in the face of unreliable name servers, and also better privacy---often the result of host name lookups is in local cache, so external name servers do not even need to be queried.

 -- Variable: syslog-service-type
     Type of the service that runs the syslog daemon, whose value is a <syslog-configuration> object.

To have a modified syslog-configuration come into effect after reconfiguring your system, the reload action should be preferred to restarting the service, as many services such as the login manager depend on it and would be restarted as well:

     # herd reload syslog

which will cause the running syslogd process to reload its configuration.

 -- Data Type: syslog-configuration
     Data type representing the configuration of the syslog daemon.

     syslogd (default: #~(string-append #$inetutils "/libexec/syslogd"))
          The syslog daemon to use.

     config-file (default: %default-syslog.conf)
          The syslog configuration file to use. See syslogd invocation (GNU Inetutils), for more information on the configuration file syntax.

 -- Variable: guix-service-type
     This is the type of the service that runs the build daemon, guix-daemon (see Invoking guix-daemon).  Its value must be a guix-configuration record as described below.

 -- Data Type: guix-configuration
     This data type represents the configuration of the Guix build daemon. See Invoking guix-daemon, for more information.

     guix (default: GUIX)
          The Guix package to use.

     build-group (default: "guixbuild")
          Name of the group for build user accounts.

     build-accounts (default: 10)
          Number of build user accounts to create.

     authorize-key? (default: #t)
          Whether to authorize the substitute keys listed in authorized-keys---by default that of ci.guix.gnu.org and bordeaux.guix.gnu.org (see Substitutes).

          When authorize-key? is true, /etc/guix/acl cannot be changed by invoking guix archive --authorize.  You must instead adjust guix-configuration as you wish and reconfigure the system.  This ensures that your operating system configuration file is self-contained.

               When booting or reconfiguring to a system where authorize-key? is true, the existing /etc/guix/acl file is backed up as /etc/guix/acl.bak if it was determined to be a manually modified file.  This is to facilitate migration from earlier versions, which allowed for in-place modifications to /etc/guix/acl.

     authorized-keys (default: %default-authorized-guix-keys)
          The list of authorized key files for archive imports, as a list of string-valued gexps (see Invoking guix archive).  By default, it contains that of ci.guix.gnu.org and bordeaux.guix.gnu.org (see Substitutes).  See substitute-urls below for an example on how to change it.

     use-substitutes? (default: #t)
          Whether to use substitutes.

     substitute-urls (default: %default-substitute-urls)
          The list of URLs where to look for substitutes by default.

          Suppose you would like to fetch substitutes from guix.example.org in addition to ci.guix.gnu.org.  You will need to do two things: (1) add guix.example.org to substitute-urls, and (2) authorize its signing key, having done appropriate checks (see Substitute Server Authorization).  The configuration below does exactly that:

               (guix-configuration
                 (substitute-urls
                  (append (list "https://guix.example.org")
                          %default-substitute-urls))
                 (authorized-keys
                  (append (list (local-file "./guix.example.org-key.pub"))
                          %default-authorized-guix-keys)))

          This example assumes that the file ./guix.example.org-key.pub contains the public key that guix.example.org uses to sign substitutes.

     generate-substitute-key? (default: #t)
          Whether to generate a substitute key pair under /etc/guix/signing-key.pub and /etc/guix/signing-key.sec if there is not already one.

          This key pair is used when exporting store items, for instance with guix publish (see Invoking guix publish) or guix archive (see Invoking guix archive).  Generating a key pair takes a few seconds when enough entropy is available and is only done once; you might want to turn it off for instance in a virtual machine that does not need it and where the extra boot time is a problem.

     max-silent-time (default: 3600)
     timeout (default: (* 3600 24))
          The number of seconds of silence and the number of seconds of activity, respectively, after which a build process times out.  A value of zero disables the timeout.

     log-compression (default: 'gzip)
          The type of compression used for build logs---one of gzip, bzip2, or none.

     discover? (default: #f)
          Whether to discover substitute servers on the local network using mDNS and DNS-SD.

     build-machines (default: #f)
          This field must be either #f or a list of gexps evaluating to a build-machine record or to a list of build-machine records (see Daemon Offload Setup).

          When it is #f, the /etc/guix/machines.scm file is left untouched.  Otherwise, the list of of gexps is written to /etc/guix/machines.scm; if a previously-existing file is found, it is backed up as /etc/guix/machines.scm.bak.  This allows you to declare build machines for offloading directly in the operating system declaration, like so:

               (guix-configuration
                 (build-machines
                   (list #~(build-machine (name "foo.example.org") ...)
                         #~(build-machine (name "bar.example.org") ...))))

          Additional build machines may be added via the guix-extension mechanism (see below).

     extra-options (default: '())
          List of extra command-line options for guix-daemon.

     log-file (default: "/var/log/guix-daemon.log")
          File where guix-daemon's standard output and standard error are written.

     http-proxy (default: #f)
          The URL of the HTTP and HTTPS proxy used for downloading fixed-output derivations and substitutes.

          It is also possible to change the daemon's proxy at run time through the set-http-proxy action, which restarts it:

               herd set-http-proxy guix-daemon http://localhost:8118

          To clear the proxy settings, run:

               herd set-http-proxy guix-daemon

     tmpdir (default: #f)
          A directory path where the guix-daemon will perform builds.

     environment (default: '())
          Environment variables to be set before starting the daemon, as a list of key=value strings.

 -- Data Type: guix-extension
     This data type represents the parameters of the Guix build daemon that are extendable. This is the type of the object that must be used within a guix service extension. See Service Composition, for more information.

     authorized-keys (default: '())
          A list of file-like objects where each element contains a public key.

     substitute-urls (default: '())
          A list of strings where each element is a substitute URL.

     build-machines (default: '())
          A list of gexps that evaluate to build-machine records or to a list of build-machine records. (see Daemon Offload Setup).

          Using this field, a service may add new build machines to receive builds offloaded by the daemon.  This is useful for a service such as hurd-vm-service-type, which can make a GNU/Hurd virtual machine directly usable for offloading (see hurd-vm-service-type).

     chroot-directories (default: '())
          A list of file-like objects or strings pointing to additional directories the build daemon can use.

 -- Variable: udev-service-type
     Type of the service that runs udev, a service which populates the /dev directory dynamically, whose value is a <udev-configuration> object.

     This service type can be extended using procedures udev-rules-service along with file->udev-rule or udev-rule which simplify the process of writing udev rules.

 -- Data Type: udev-configuration
     Data type representing the configuration of udev.

     udev (default: eudev) (type: file-like)
          Package object of the udev service.

     rules (default: '()) (type: list-of-file-like)
          List of file-like objects denoting udev-rule files.

 -- Procedure: udev-rule FILE-NAME CONTENTS
     Return a udev-rule file named FILE-NAME containing the rules defined by the CONTENTS literal.

     In the following example, a rule for a USB device is defined to be stored in the file 90-usb-thing.rules.  The rule runs a script upon detecting a USB device with a given product identifier.

          (define %example-udev-rule
            (udev-rule
              "90-usb-thing.rules"
              (string-append "ACTION==\"add\", SUBSYSTEM==\"usb\", "
                             "ATTR{product}==\"Example\", "
                             "RUN+=\"/path/to/script\"")))

 -- Procedure: udev-rules-service NAME RULES [#:groups '()]
     Return a service that extends udev-service-type with RULES and account-service-type with GROUPS as system groups. This works by creating a singleton service type NAME-udev-rules, of which the returned service is an instance.

     Here we show how it can be used to extend udev-service-type with the previously defined rule %example-udev-rule.

          (operating-system
           ;; ...
           (services
             (cons (udev-rules-service 'usb-thing %example-udev-rule)
                   %desktop-services)))

 -- Procedure: file->udev-rule FILE-NAME FILE
     Return a udev-rule file named FILE-NAME containing the rules defined within FILE, a file-like object.

     The following example showcases how we can use an existing rule file.

          (use-modules (guix download)     ;for url-fetch
                       (guix packages)     ;for origin
                       ...)

          (define %android-udev-rules
            (file->udev-rule
              "51-android-udev.rules"
              (let ((version "20170910"))
                (origin
                 (method url-fetch)
                 (uri (string-append "https://raw.githubusercontent.com/M0Rf30/"
                                     "android-udev-rules/" version "/51-android.rules"))
                 (sha256
                  (base32 "0lmmagpyb6xsq6zcr2w1cyx9qmjqmajkvrdbhjx32gqf1d9is003"))))))

Additionally, Guix package definitions can be included in RULES in order to extend the udev rules with the definitions found under their lib/udev/rules.d sub-directory.  In lieu of the previous FILE->UDEV-RULE example, we could have used the ANDROID-UDEV-RULES package which exists in Guix in the (gnu packages android) module.

The following example shows how to use the ANDROID-UDEV-RULES package so that the Android tool adb can detect devices without root privileges.  It also details how to create the adbusers group, which is required for the proper functioning of the rules defined within the android-udev-rules package.  To create such a group, we must define it both as part of the supplementary-groups of our user-account declaration, as well as in the GROUPS of the udev-rules-service procedure.

     (use-modules (gnu packages android)  ;for android-udev-rules
                  (gnu system shadow)     ;for user-group
                  ...)

     (operating-system
       ;; ...
       (users (cons (user-account
                     ;; ...
                     (supplementary-groups
                      '("adbusers"   ;for adb
                        "wheel" "netdev" "audio" "video")))))
       ;; ...
       (services
         (cons (udev-rules-service 'android android-udev-rules
                                   #:groups '("adbusers"))
               %desktop-services)))

 -- Variable: urandom-seed-service-type
     Save some entropy in %random-seed-file to seed /dev/urandom when rebooting.  It also tries to seed /dev/urandom from /dev/hwrng while booting, if /dev/hwrng exists and is readable.

 -- Variable: %random-seed-file
     This is the name of the file where some random bytes are saved by URANDOM-SEED-SERVICE to seed /dev/urandom when rebooting. It defaults to /var/lib/random-seed.

 -- Variable: gpm-service-type
     This is the type of the service that runs GPM, the general-purpose mouse daemon, which provides mouse support to the Linux console.  GPM allows users to use the mouse in the console, notably to select, copy, and paste text.

     The value for services of this type must be a gpm-configuration (see below).  This service is not part of %base-services.

 -- Data Type: gpm-configuration
     Data type representing the configuration of GPM.

     options (default: %default-gpm-options)
          Command-line options passed to gpm.  The default set of options instruct gpm to listen to mouse events on /dev/input/mice.  See Command Line (gpm manual), for more information.

     gpm (default: gpm)
          The GPM package to use.

 -- Variable: guix-publish-service-type
     This is the service type for guix publish (see Invoking guix publish).  Its value must be a guix-publish-configuration object, as described below.

     This assumes that /etc/guix already contains a signing key pair as created by guix archive --generate-key (see Invoking guix archive).  If that is not the case, the service will fail to start.

 -- Data Type: guix-publish-configuration
     Data type representing the configuration of the guix publish service.

     guix (default: guix)
          The Guix package to use.

     port (default: 80)
          The TCP port to listen for connections.

     host (default: "localhost")
          The host (and thus, network interface) to listen to.  Use "0.0.0.0" to listen on all the network interfaces.

     advertise? (default: #f)
          When true, advertise the service on the local network via the DNS-SD protocol, using Avahi.

          This allows neighboring Guix devices with discovery on (see guix-configuration above) to discover this guix publish instance and to automatically download substitutes from it.

     compression (default: '(("gzip" 3) ("zstd" 3)))
          This is a list of compression method/level tuple used when compressing substitutes.  For example, to compress all substitutes with both lzip at level 7 and gzip at level 9, write:

               '(("lzip" 7) ("gzip" 9))

          Level 9 achieves the best compression ratio at the expense of increased CPU usage, whereas level 1 achieves fast compression.  See Invoking guix publish, for more information on the available compression methods and the tradeoffs involved.

          An empty list disables compression altogether.

     nar-path (default: "nar")
          The URL path at which ``nars'' can be fetched.  See --nar-path, for details.

     cache (default: #f)
          When it is #f, disable caching and instead generate archives on demand.  Otherwise, this should be the name of a directory---e.g., "/var/cache/guix/publish"---where guix publish caches archives and meta-data ready to be sent.  See --cache, for more information on the tradeoffs involved.

     workers (default: #f)
          When it is an integer, this is the number of worker threads used for caching; when #f, the number of processors is used. See --workers, for more information.

     cache-bypass-threshold (default: 10 MiB)
          When cache is true, this is the maximum size in bytes of a store item for which guix publish may bypass its cache in case of a cache miss.  See --cache-bypass-threshold, for more information.

     ttl (default: #f)
          When it is an integer, this denotes the time-to-live in seconds of the published archives.  See --ttl, for more information.

     negative-ttl (default: #f)
          When it is an integer, this denotes the time-to-live in seconds for the negative lookups.  See --negative-ttl, for more information.

 -- Variable: rngd-service-type
     Type of the service that runs rng-tools rngd, whose value is an <rngd-configuration> object.

 -- Data Type: rngd-configuration
     Data type representing the configuration of rngd.

     rng-tools (default: rng-tools) (type: file-like)
          Package object of the rng-tools rngd.

     device (default: "/DEV/HWRNG") (type: string)
          Path of the device to add to the kernel's entropy pool.  The service will fail if DEVICE does not exist.

 -- Variable: pam-limits-service-type
     Type of the service that installs a configuration file for the pam_limits module (http://linux-pam.org/Linux-PAM-html/sag-pam_limits.html).  The value for this service type is a list of pam-limits-entry values, which can be used to specify ulimit limits and nice priority limits to user sessions. By default, the value is the empty list.

     The following limits definition sets two hard and soft limits for all login sessions of users in the realtime group:

          (service pam-limits-service-type
                   (list
                    (pam-limits-entry "@realtime" 'both 'rtprio 99)
                    (pam-limits-entry "@realtime" 'both 'memlock 'unlimited)))

     The first entry increases the maximum realtime priority for non-privileged processes; the second entry lifts any restriction of the maximum address space that can be locked in memory.  These settings are commonly used for real-time audio systems.

     Another useful example is raising the maximum number of open file descriptors that can be used:

          (service pam-limits-service-type
                   (list
                    (pam-limits-entry "*" 'both 'nofile 100000)))

     In the above example, the asterisk means the limit should apply to any user.  It is important to ensure the chosen value doesn't exceed the maximum system value visible in the /proc/sys/fs/file-max file, else the users would be prevented from login in.  For more information about the Pluggable Authentication Module (PAM) limits, refer to the pam_limits man page from the linux-pam package.

 -- Variable: greetd-service-type
     greetd (https://git.sr.ht/~kennylevinsen/greetd) is a minimal and flexible login manager daemon, that makes no assumptions about what you want to launch.

     If you can run it from your shell in a TTY, greetd can start it. If it can be taught to speak a simple JSON-based IPC protocol, then it can be a geeter.

     greetd-service-type provides necessary infrastructure for logging in users, including:

       * greetd PAM service

       * Special variation of pam-mount to mount XDG_RUNTIME_DIR

     Here is an example of switching from mingetty-service-type to greetd-service-type, and how different terminals could be:

            (append
             (modify-services %base-services
               ;; greetd-service-type provides "greetd" PAM service
               (delete login-service-type)
               ;; and can be used in place of mingetty-service-type
               (delete mingetty-service-type))
             (list
              (service greetd-service-type
                       (greetd-configuration
                        (terminals
                         (list
                          ;; we can make any terminal active by default
                          (greetd-terminal-configuration (terminal-vt "1") (terminal-switch #t))
                          ;; we can make environment without XDG_RUNTIME_DIR set
                          ;; even provide our own environment variables
                          (greetd-terminal-configuration
                           (terminal-vt "2")
                           (default-session-command
                             (greetd-agreety-session
                              (extra-env '(("MY_VAR" . "1")))
                              (xdg-env? #f))))
                          ;; we can use different shell instead of default bash
                          (greetd-terminal-configuration
                           (terminal-vt "3")
                           (default-session-command
                             (greetd-agreety-session (command (file-append zsh "/bin/zsh")))))
                          ;; we can use any other executable command as greeter
                          (greetd-terminal-configuration
                           (terminal-vt "4")
                           (default-session-command (program-file "my-noop-greeter" #~(exit))))
                          (greetd-terminal-configuration (terminal-vt "5"))
                          (greetd-terminal-configuration (terminal-vt "6"))))))
              ;; mingetty-service-type can be used in parallel
              ;; if needed to do so, do not (delete login-service-type)
              ;; as illustrated above
              #| (service mingetty-service-type (mingetty-configuration (tty "tty8"))) |#))

 -- Data Type: greetd-configuration
     Configuration record for the greetd-service-type.

     motd
          A file-like object containing the ``message of the day''.

     allow-empty-passwords? (default: #t)
          Allow empty passwords by default so that first-time users can log in when the 'root' account has just been created.

     terminals (default: '())
          List of greetd-terminal-configuration per terminal for which greetd should be started.

     greeter-supplementary-groups (default: '())
          List of groups which should be added to greeter user. For instance:

               (greeter-supplementary-groups '("seat" "video"))

          Note that this example will fail if seat group does not exist.

 -- Data Type: greetd-terminal-configuration
     Configuration record for per terminal greetd daemon service.

     greetd (default: greetd)
          The greetd package to use.

     config-file-name
          Configuration file name to use for greetd daemon. Generally, autogenerated derivation based on terminal-vt value.

     log-file-name
          Log file name to use for greetd daemon. Generally, autogenerated name based on terminal-vt value.

     terminal-vt (default: "7")
          The VT to run on. Use of a specific VT with appropriate conflict avoidance is recommended.

     terminal-switch (default: #f)
          Make this terminal active on start of greetd.

     source-profile? (default: #t)
          Whether to source /etc/profile and ~/.profile, when they exist.

     default-session-user (default: "greeter")
          The user to use for running the greeter.

     default-session-command (default: (greetd-agreety-session))
          Can be either instance of greetd-agreety-session configuration or gexp->script like object to use as greeter.

 -- Data Type: greetd-agreety-session
     Configuration record for the agreety greetd greeter.

     agreety (default: greetd)
          The package with /bin/agreety command.

     command (default: (file-append bash "/bin/bash"))
          Command to be started by /bin/agreety on successful login.

     command-args (default: '("-l"))
          Command arguments to pass to command.

     extra-env (default: '())
          Extra environment variables to set on login.

     xdg-env? (default: #t)
          If true XDG_RUNTIME_DIR and XDG_SESSION_TYPE will be set before starting command. One should note that, extra-env variables are set right after mentioned variables, so that they can be overridden.

 -- Data Type: greetd-wlgreet-session
     Generic configuration record for the wlgreet greetd greeter.

     wlgreet (default: wlgreet)
          The package with the /bin/wlgreet command.

     command (default: (file-append sway "/bin/sway"))
          Command to be started by /bin/wlgreet on successful login.

     command-args (default: '())
          Command arguments to pass to command.

     output-mode (default: "all")
          Option to use for outputMode in the TOML configuration file.

     scale (default: 1)
          Option to use for scale in the TOML configuration file.

     background (default: '(0 0 0 0.9))
          RGBA list to use as the background colour of the login prompt.

     headline (default: '(1 1 1 1))
          RGBA list to use as the headline colour of the UI popup.

     prompt (default: '(1 1 1 1))
          RGBA list to use as the prompt colour of the UI popup.

     prompt-error (default: '(1 1 1 1))
          RGBA list to use as the error colour of the UI popup.

     border (default: '(1 1 1 1))
          RGBA list to use as the border colour of the UI popup.

     extra-env (default: '())
          Extra environment variables to set on login.

 -- Data Type: greetd-wlgreet-sway-session
     Sway-specific configuration record for the wlgreet greetd greeter.

     wlgreet-session (default: (greetd-wlgreet-session))
          A greetd-wlgreet-session record for generic wlgreet configuration, on top of the Sway-specific greetd-wlgreet-sway-session.

     sway (default: sway)
          The package providing the /bin/sway command.

     sway-configuration (default: #f)
          File-like object providing an additional Sway configuration file to be prepended to the mandatory part of the configuration.

     Here is an example of a greetd configuration that uses wlgreet and Sway:

            (greetd-configuration
             ;; We need to give the greeter user these permissions, otherwise
             ;; Sway will crash on launch.
             (greeter-supplementary-groups (list "video" "input" "seat"))
             (terminals
              (list (greetd-terminal-configuration
                     (terminal-vt "1")
                     (terminal-switch #t)
                     (default-session-command
                      (greetd-wlgreet-sway-session
                       (sway-configuration
                        (local-file "sway-greetd.conf"))))))))

Scheduled Job Execution
-----------------------

The (gnu services mcron) module provides an interface to GNU mcron, a daemon to run jobs at scheduled times (see GNU mcron).  GNU mcron is similar to the traditional Unix cron daemon; the main difference is that it is implemented in Guile Scheme, which provides a lot of flexibility when specifying the scheduling of jobs and their actions.

The example below defines an operating system that runs the updatedb (see Invoking updatedb (Finding Files)) and the guix gc commands (see Invoking guix gc) daily, as well as the mkid command on behalf of an unprivileged user (see mkid invocation (ID Database Utilities)).  It uses gexps to introduce job definitions that are passed to mcron (see G-Expressions).

     (use-modules (guix) (gnu) (gnu services mcron))
     (use-package-modules base idutils)

     (define updatedb-job
       ;; Run 'updatedb' at 3AM every day.  Here we write the
       ;; job's action as a Scheme procedure.
       #~(job '(next-hour '(3))
              (lambda ()
                (system* (string-append #$findutils "/bin/updatedb")
                         "--prunepaths=/tmp /var/tmp /gnu/store"))
              "updatedb"))

     (define garbage-collector-job
       ;; Collect garbage 5 minutes after midnight every day.
       ;; The job's action is a shell command.
       #~(job "5 0 * * *"            ;Vixie cron syntax
              "guix gc -F 1G"))

     (define idutils-job
       ;; Update the index database as user "charlie" at 12:15PM
       ;; and 19:15PM.  This runs from the user's home directory.
       #~(job '(next-minute-from (next-hour '(12 19)) '(15))
              (string-append #$idutils "/bin/mkid src")
              #:user "charlie"))

     (operating-system
       ;; ...

       ;; %BASE-SERVICES already includes an instance of
       ;; 'mcron-service-type', which we extend with additional
       ;; jobs using 'simple-service'.
       (services (cons (simple-service 'my-cron-jobs
                                        mcron-service-type
                                        (list garbage-collector-job
                                              updatedb-job
                                              idutils-job))
                       %base-services)))

     When providing the action of a job specification as a procedure, you should provide an explicit name for the job via the optional 3rd argument as done in the updatedb-job example above.  Otherwise, the job would appear as ``Lambda function'' in the output of herd schedule mcron, which is not nearly descriptive enough!

     Avoid calling the Guile procedures execl, execle or execlp inside a job specification, else mcron won't be able to output the completion status of the job.

For more complex jobs defined in Scheme where you need control over the top level, for instance to introduce a use-modules form, you can move your code to a separate program using the program-file procedure of the (guix gexp) module (see G-Expressions).  The example below illustrates that.

     (define %battery-alert-job
       ;; Beep when the battery percentage falls below %MIN-LEVEL.
       #~(job
          '(next-minute (range 0 60 1))
          #$(program-file
             "battery-alert.scm"
             (with-imported-modules (source-module-closure
                                     '((guix build utils)))
               #~(begin
                   (use-modules (guix build utils)
                                (ice-9 popen)
                                (ice-9 regex)
                                (ice-9 textual-ports)
                                (srfi srfi-2))

                   (define %min-level 20)

                   (setenv "LC_ALL" "C")     ;ensure English output
                   (and-let* ((input-pipe (open-pipe*
                                           OPEN_READ
                                           #$(file-append acpi "/bin/acpi")))
                              (output (get-string-all input-pipe))
                              (m (string-match "Discharging, ([0-9]+)%" output))
                              (level (string->number (match:substring m 1)))
                              ((< level %min-level)))
                     (format #t "warning: Battery level is low (~a%)~%" level)
                     (invoke #$(file-append beep "/bin/beep") "-r5")))))))

See mcron job specifications (GNU mcron), for more information on mcron job specifications.  Below is the reference of the mcron service.

On a running system, you can use the schedule action of the service to visualize the mcron jobs that will be executed next:

     # herd schedule mcron

The example above lists the next five tasks that will be executed, but you can also specify the number of tasks to display:

     # herd schedule mcron 10

 -- Variable: mcron-service-type
     This is the type of the mcron service, whose value is an mcron-configuration object.

     This service type can be the target of a service extension that provides additional job specifications (see Service Composition).  In other words, it is possible to define services that provide additional mcron jobs to run.

 -- Data Type: mcron-configuration
     Available mcron-configuration fields are:

     mcron (default: mcron) (type: file-like)
          The mcron package to use.

     jobs (default: '()) (type: list-of-gexps)
          This is a list of gexps (see G-Expressions), where each gexp corresponds to an mcron job specification (see mcron job specifications (GNU mcron)).

     log? (default: #t) (type: boolean)
          Log messages to standard output.

     log-file (default: "/var/log/mcron.log") (type: string)
          Log file location.

     log-format (default: "~1@*~a ~a: ~a~%") (type: string)
          (ice-9 format) format string for log messages.  The default value produces messages like PID NAME: MESSAGE (see Invoking (GNU mcron)).  Each message is also prefixed by a timestamp by GNU Shepherd.

     date-format (type: maybe-string)
          (srfi srfi-19) format string for date.

Log Rotation
------------

Log files such as those found in /var/log tend to grow endlessly, so it's a good idea to rotate them once in a while---i.e., archive their contents in separate files, possibly compressed.  The (gnu services admin) module provides an interface to GNU Rot[t]log, a log rotation tool (see GNU Rot[t]log Manual).

This service is part of %base-services, and thus enabled by default, with the default settings, for commonly encountered log files. The example below shows how to extend it with an additional rotation, should you need to do that (usually, services that produce log files already take care of that):

     (use-modules (guix) (gnu))
     (use-service-modules admin)

     (define my-log-files
       ;; Log files that I want to rotate.
       '("/var/log/something.log" "/var/log/another.log"))

     (operating-system
       ;; ...
       (services (cons (simple-service 'rotate-my-stuff
                                       rottlog-service-type
                                       (list (log-rotation
                                              (frequency 'daily)
                                              (files my-log-files))))
                       %base-services)))

 -- Variable: rottlog-service-type
     This is the type of the Rottlog service, whose value is a rottlog-configuration object.

     Other services can extend this one with new log-rotation objects (see below), thereby augmenting the set of files to be rotated.

     This service type can define mcron jobs (see Scheduled Job Execution) to run the rottlog service.

 -- Data Type: rottlog-configuration
     Data type representing the configuration of rottlog.

     rottlog (default: rottlog)
          The Rottlog package to use.

     rc-file (default: (file-append rottlog "/etc/rc"))
          The Rottlog configuration file to use (see Mandatory RC Variables (GNU Rot[t]log Manual)).

     rotations (default: %default-rotations)
          A list of log-rotation objects as defined below.

     jobs
          This is a list of gexps where each gexp corresponds to an mcron job specification (see Scheduled Job Execution).

 -- Data Type: log-rotation
     Data type representing the rotation of a group of log files.

     Taking an example from the Rottlog manual (see Period Related File Examples (GNU Rot[t]log Manual)), a log rotation might be defined like this:

          (log-rotation
            (frequency 'daily)
            (files '("/var/log/apache/*"))
            (options '("storedir apache-archives"
                       "rotate 6"
                       "notifempty"
                       "nocompress")))

     The list of fields is as follows:

     frequency (default: 'weekly)
          The log rotation frequency, a symbol.

     files
          The list of files or file glob patterns to rotate.

     options (default: %default-log-rotation-options)
          The list of rottlog options for this rotation (see Configuration parameters (GNU Rot[t]log Manual)).

     post-rotate (default: #f)
          Either #f or a gexp to execute once the rotation has completed.

 -- Variable: %default-rotations
     Specifies weekly rotation of %rotated-files and of /var/log/guix-daemon.log.

 -- Variable: %rotated-files
     The list of syslog-controlled files to be rotated.  By default it is: '("/var/log/messages" "/var/log/secure" "/var/log/debug" \ "/var/log/maillog").

Some log files just need to be deleted periodically once they are old, without any other criterion and without any archival step.  This is the case of build logs stored by guix-daemon under /var/log/guix/drvs (see Invoking guix-daemon).  The log-cleanup service addresses this use case.  For example, %base-services (see Base Services) includes the following:

     ;; Periodically delete old build logs.
     (service log-cleanup-service-type
              (log-cleanup-configuration
               (directory "/var/log/guix/drvs")))

That ensures build logs do not accumulate endlessly.

 -- Variable: log-cleanup-service-type
     This is the type of the service to delete old logs.  Its value must be a log-cleanup-configuration record as described below.

 -- Data Type: log-cleanup-configuration
     Data type representing the log cleanup configuration

     directory
          Name of the directory containing log files.

     expiry (default: (* 6 30 24 3600))
          Age in seconds after which a file is subject to deletion (six months by default).

     schedule (default: "30 12 01,08,15,22 * *")
          String or gexp denoting the corresponding mcron job schedule (see Scheduled Job Execution).

Anonip Service
--------------

Anonip is a privacy filter that removes IP address from web server logs. This service creates a FIFO and filters any written lines with anonip before writing the filtered log to a target file.

The following example sets up the FIFO /var/run/anonip/https.access.log and writes the filtered log file /var/log/anonip/https.access.log.

     (service anonip-service-type
              (anonip-configuration
                (input  "/var/run/anonip/https.access.log")
                (output "/var/log/anonip/https.access.log")))

Configure your web server to write its logs to the FIFO at /var/run/anonip/https.access.log and collect the anonymized log file at /var/web-logs/https.access.log.

 -- Data Type: anonip-configuration
     This data type represents the configuration of anonip. It has the following parameters:

     anonip (default: anonip)
          The anonip package to use.

     input
          The file name of the input log file to process.  The service creates a FIFO of this name.  The web server should write its logs to this FIFO.

     output
          The file name of the processed log file.

     The following optional settings may be provided:

     skip-private?
          When #true do not mask addresses in private ranges.

     column
          A 1-based indexed column number.  Assume IP address is in the specified column (default is 1).

     replacement
          Replacement string in case address parsing fails, e.g. "0.0.0.0".

     ipv4mask
          Number of bits to mask in IPv4 addresses.

     ipv6mask
          Number of bits to mask in IPv6 addresses.

     increment
          Increment the IP address by the given number.  By default this is zero.

     delimiter
          Log delimiter string.

     regex
          Regular expression for detecting IP addresses.  Use this instead of column.

Networking Setup
----------------

The (gnu services networking) module provides services to configure network interfaces and set up networking on your machine. Those services provide different ways for you to set up your machine: by declaring a static network configuration, by running a Dynamic Host Configuration Protocol (DHCP) client, or by running daemons such as NetworkManager and Connman that automate the whole process, automatically adapt to connectivity changes, and provide a high-level user interface.

On a laptop, NetworkManager and Connman are by far the most convenient options, which is why the default desktop services include NetworkManager (see %desktop-services). For a server, or for a virtual machine or a container, static network configuration or a simple DHCP client are often more appropriate.

This section describes the various network setup services available, starting with static network configuration.

 -- Variable: static-networking-service-type
     This is the type for statically-configured network interfaces.  Its value must be a list of static-networking records.  Each of them declares a set of addresses, routes, and links, as shown below.

     Here is the simplest configuration, with only one network interface controller (NIC) and only IPv4 connectivity:

          ;; Static networking for one NIC, IPv4-only.
          (service static-networking-service-type
                   (list (static-networking
                          (addresses
                           (list (network-address
                                  (device "eno1")
                                  (value "10.0.2.15/24"))))
                          (routes
                           (list (network-route
                                  (destination "default")
                                  (gateway "10.0.2.2"))))
                          (name-servers '("10.0.2.3")))))

     The snippet above can be added to the services field of your operating system configuration (see Using the Configuration System). It will configure your machine to have 10.0.2.15 as its IP address, with a 24-bit netmask for the local network---meaning that any 10.0.2.X address is on the local area network (LAN).  Traffic to addresses outside the local network is routed via 10.0.2.2.  Host names are resolved by sending domain name system (DNS) queries to 10.0.2.3.

 -- Data Type: static-networking
     This is the data type representing a static network configuration.

     As an example, here is how you would declare the configuration of a machine with a single network interface controller (NIC) available as eno1, and with one IPv4 and one IPv6 address:

          ;; Network configuration for one NIC, IPv4 + IPv6.
          (static-networking
           (addresses (list (network-address
                             (device "eno1")
                             (value "10.0.2.15/24"))
                            (network-address
                             (device "eno1")
                             (value "2001:123:4567:101::1/64"))))
           (routes (list (network-route
                          (destination "default")
                          (gateway "10.0.2.2"))
                         (network-route
                          (destination "default")
                          (gateway "2020:321:4567:42::1"))))
           (name-servers '("10.0.2.3")))

     If you are familiar with the ip command of the iproute2 package (https://wiki.linuxfoundation.org/networking/iproute2) found on Linux-based systems, the declaration above is equivalent to typing:

          ip address add 10.0.2.15/24 dev eno1
          ip address add 2001:123:4567:101::1/64 dev eno1
          ip route add default via inet 10.0.2.2
          ip route add default via inet6 2020:321:4567:42::1

     Run man 8 ip for more info.  Venerable GNU/Linux users will certainly know how to do it with ifconfig and route, but we'll spare you that.

     The available fields of this data type are as follows:

     addresses
     links (default: '())
     routes (default: '())
          The list of network-address, network-link, and network-route records for this network (see below).

     name-servers (default: '())
          The list of IP addresses (strings) of domain name servers.  These IP addresses go to /etc/resolv.conf.

     provision (default: '(networking))
          If true, this should be a list of symbols for the Shepherd service corresponding to this network configuration.

     requirement (default '())
          The list of Shepherd services depended on.

 -- Data Type: network-address
     This is the data type representing the IP address of a network interface.

     device
          The name of the network interface for this address---e.g., "eno1".

     value
          The actual IP address and network mask, in CIDR (Classless Inter-Domain Routing) notation (https://en.wikipedia.org/wiki/CIDR#CIDR_notation), as a string.

          For example, "10.0.2.15/24" denotes IPv4 address 10.0.2.15 on a 24-bit sub-network---all 10.0.2.X addresses are on the same local network.

     ipv6?
          Whether value denotes an IPv6 address.  By default this is automatically determined.

 -- Data Type: network-route
     This is the data type representing a network route.

     destination
          The route destination (a string), either an IP address and network mask or "default" to denote the default route.

     source (default: #f)
          The route source.

     device (default: #f)
          The device used for this route---e.g., "eno2".

     ipv6? (default: auto)
          Whether this is an IPv6 route.  By default this is automatically determined based on destination or gateway.

     gateway (default: #f)
          IP address (a string) through which traffic is routed.

 -- Data Type: network-link
     Data type for a network link (see Link (Guile-Netlink Manual)).  During startup, network links are employed to construct or modify existing or virtual ethernet links.  These ethernet links can be identified by their NAME or MAC-ADDRESS.  If there is a need to create virtual interface, NAME and TYPE fields are required.

     name
          The name of the link---e.g., "v0p0" (default: #f).

     type
          A symbol denoting the type of the link---e.g., 'veth (default: #f).

     mac-address
          The mac-address of the link---e.g., "98:11:22:33:44:55" (default: #f).

     arguments
          List of arguments for this type of link.

Consider a scenario where a server equipped with a network interface which has multiple ports.  These ports are connected to a switch, which supports link aggregation (https://en.wikipedia.org/wiki/Link_aggregation) (also known as bonding or NIC teaming).  The switch uses port channels to consolidate multiple physical interfaces into one logical interface to provide higher bandwidth, load balancing, and link redundancy.  When a port is added to a LAG (or link aggregation group), it inherits the properties of the port-channel.  Some of these properties are VLAN membership, trunk status, and so on.

VLAN (https://en.wikipedia.org/wiki/Virtual_LAN) (or virtual local area network) is a logical network that is isolated from other VLANs on the same physical network.  This can be used to segregate traffic, improve security, and simplify network management.

With all that in mind let's configure our static network for the server. We will bond two existing interfaces together using 802.3ad schema and on top of it, build a VLAN interface with id 1055.  We assign a static ip to our new VLAN interface.

     (static-networking
      (links (list (network-link
                    (name "bond0")
                    (type 'bond)
                    (arguments '((mode . "802.3ad")
                                 (miimon . 100)
                                 (lacp-active . "on")
                                 (lacp-rate . "fast"))))

                   (network-link
                    (mac-address "98:11:22:33:44:55")
                    (arguments '((master . "bond0"))))

                   (network-link
                    (mac-address "98:11:22:33:44:56")
                    (arguments '((master . "bond0"))))

                   (network-link
                    (name "bond0.1055")
                    (type 'vlan)
                    (arguments '((id . 1055)
                                 (link . "bond0"))))))
      (addresses (list (network-address
                        (value "192.168.1.4/24")
                        (device "bond0.1055")))))

 -- Variable: %loopback-static-networking
     This is the static-networking record representing the ``loopback device'', lo, for IP addresses 127.0.0.1 and ::1, and providing the loopback Shepherd service.

 -- Variable: %qemu-static-networking
     This is the static-networking record representing network setup when using QEMU's user-mode network stack on eth0 (see Using the user mode network stack (QEMU Documentation)).

 -- Variable: dhcp-client-service-type
     This is the type of services that run DHCP, a Dynamic Host Configuration Protocol (DHCP) client.

 -- Data Type: dhcp-client-configuration
     Data type representing the configuration of the DHCP client service.

     package (default: isc-dhcp)
          DHCP client package to use.

     interfaces (default: 'all)
          Either 'all or the list of interface names that the DHCP client should listen on---e.g., '("eno1").

          When set to 'all, the DHCP client listens on all the available non-loopback interfaces that can be activated.  Otherwise the DHCP client listens only on the specified interfaces.

     shepherd-requirement (default: '())
     shepherd-provision (default: '(networking))
          This option can be used to provide a list of symbols naming Shepherd services that this service will depend on, such as 'wpa-supplicant or 'iwd if you require authenticated access for encrypted WiFi or Ethernet networks.

          Likewise, shepherd-provision is a list of Shepherd service names (symbols) provided by this service.  You might want to change the default value if you intend to run several DHCP clients, only one of which provides the networking Shepherd service.

 -- Variable: network-manager-service-type
     This is the service type for the NetworkManager (https://wiki.gnome.org/Projects/NetworkManager) service. The value for this service type is a network-manager-configuration record.

     This service is part of %desktop-services (see Desktop Services).

 -- Data Type: network-manager-configuration
     Data type representing the configuration of NetworkManager.

     network-manager (default: network-manager)
          The NetworkManager package to use.

     shepherd-requirement (default: '(wpa-supplicant))
          This option can be used to provide a list of symbols naming Shepherd services that this service will depend on, such as 'wpa-supplicant or 'iwd if you require authenticated access for encrypted WiFi or Ethernet networks.

     dns (default: "default")
          Processing mode for DNS, which affects how NetworkManager uses the resolv.conf configuration file.

          default
               NetworkManager will update resolv.conf to reflect the nameservers provided by currently active connections.

          dnsmasq
               NetworkManager will run dnsmasq as a local caching nameserver, using a conditional forwarding configuration if you are connected to a VPN, and then update resolv.conf to point to the local nameserver.

               With this setting, you can share your network connection.  For example when you want to share your network connection to another laptop via an Ethernet cable, you can open nm-connection-editor and configure the Wired connection's method for IPv4 and IPv6 to be ``Shared to other computers'' and reestablish the connection (or reboot).

               You can also set up a host-to-guest connection to QEMU VMs (see Installing Guix in a VM).  With a host-to-guest connection, you can e.g. access a Web server running on the VM (see Web Services) from a Web browser on your host system, or connect to the VM via SSH (see openssh-service-type).  To set up a host-to-guest connection, run this command once:

                    nmcli connection add type tun \
                     connection.interface-name tap0 \
                     tun.mode tap tun.owner $(id -u) \
                     ipv4.method shared \
                     ipv4.addresses 172.28.112.1/24

               Then each time you launch your QEMU VM (see Running Guix in a VM), pass -nic tap,ifname=tap0,script=no,downscript=no to qemu-system-....

          none
               NetworkManager will not modify resolv.conf.

     vpn-plugins (default: '())
          This is the list of available plugins for virtual private networks (VPNs).  An example of this is the network-manager-openvpn package, which allows NetworkManager to manage VPNs via OpenVPN.

 -- Variable: connman-service-type
     This is the service type to run Connman (https://01.org/connman), a network connection manager.

     Its value must be a connman-configuration record as in this example:

          (service connman-service-type
                   (connman-configuration
                     (disable-vpn? #t)))

     See below for details about connman-configuration.

 -- Data Type: connman-configuration
     Data Type representing the configuration of connman.

     connman (default: CONNMAN)
          The connman package to use.

     shepherd-requirement (default: '())
          This option can be used to provide a list of symbols naming Shepherd services that this service will depend on, such as 'wpa-supplicant or 'iwd if you require authenticated access for encrypted WiFi or Ethernet networks.

     disable-vpn? (default: #f)
          When true, disable connman's vpn plugin.

     general-configuration (default: (connman-general-configuration))
          Configuration serialized to main.conf and passed as --config to connmand.

 -- Data Type: connman-general-configuration
     Available connman-general-configuration fields are:

     input-request-timeout (type: maybe-number)
          Set input request timeout.  Default is 120 seconds.  The request for inputs like passphrase will timeout after certain amount of time.  Use this setting to increase the value in case of different user interface designs.

     browser-launch-timeout (type: maybe-number)
          Set browser launch timeout.  Default is 300 seconds.  The request for launching a browser for portal pages will timeout after certain amount of time.  Use this setting to increase the value in case of different user interface designs.

     background-scanning? (type: maybe-boolean)
          Enable background scanning.  Default is true.  If wifi is disconnected, the background scanning will follow a simple back off mechanism from 3s up to 5 minutes.  Then, it will stay in 5 minutes unless user specifically asks for scanning through a D-Bus call.  If so, the mechanism will start again from 3s.  This feature activates also the background scanning while being connected, which is required for roaming on wifi.  When background-scanning? is false, ConnMan will not perform any scan regardless of wifi is connected or not, unless it is requested by the user through a D-Bus call.

     use-gateways-as-timeservers? (type: maybe-boolean)
          Assume that service gateways also function as timeservers.  Default is false.

     fallback-timeservers (type: maybe-list)
          List of Fallback timeservers.  These timeservers are used for NTP sync when there are no timeservers set by the user or by the service, and when use-gateways-as-timeservers? is #f.  These can contain a mixed combination of fully qualified domain names, IPv4 and IPv6 addresses.

     fallback-nameservers (type: maybe-list)
          List of fallback nameservers appended to the list of nameservers given by the service.  The nameserver entries must be in numeric format, host names are ignored.

     default-auto-connect-technologies (type: maybe-list)
          List of technologies that are marked autoconnectable by default.  The default value for this entry when empty is "ethernet", "wifi", "cellular".  Services that are automatically connected must have been set up and saved to storage beforehand.

     default-favourite-technologies (type: maybe-list)
          List of technologies that are marked favorite by default.  The default value for this entry when empty is "ethernet".  Connects to services from this technology even if not setup and saved to storage.

     always-connected-technologies (type: maybe-list)
          List of technologies which are always connected regardless of preferred-technologies setting (auto-connect? #t).  The default value is empty and this feature is disabled unless explicitly enabled.

     preferred-technologies (type: maybe-list)
          List of preferred technologies from the most preferred one to the least preferred one.  Services of the listed technology type will be tried one by one in the order given, until one of them gets connected or they are all tried.  A service of a preferred technology type in state 'ready' will get the default route when compared to another preferred type further down the list with state 'ready' or with a non-preferred type; a service of a preferred technology type in state 'online' will get the default route when compared to either a non-preferred type or a preferred type further down in the list.

     network-interface-blacklist (type: maybe-list)
          List of blacklisted network interfaces.  Found interfaces will be compared to the list and will not be handled by ConnMan, if their first characters match any of the list entries.  Default value is "vmnet", "vboxnet", "virbr", "ifb".

     allow-hostname-updates? (type: maybe-boolean)
          Allow ConnMan to change the system hostname.  This can happen for example if we receive DHCP hostname option.  Default value is #t.

     allow-domainname-updates? (type: maybe-boolean)
          Allow connman to change the system domainname.  This can happen for example if we receive DHCP domainname option.  Default value is #t.

     single-connected-technology? (type: maybe-boolean)
          Keep only a single connected technology at any time.  When a new service is connected by the user or a better one is found according to preferred-technologies, the new service is kept connected and all the other previously connected services are disconnected.  With this setting it does not matter whether the previously connected services are in 'online' or 'ready' states, the newly connected service is the only one that will be kept connected.  A service connected by the user will be used until going out of network coverage.  With this setting enabled applications will notice more network breaks than normal.  Note this options can't be used with VPNs.  Default value is #f.

     tethering-technologies (type: maybe-list)
          List of technologies that are allowed to enable tethering.  The default value is "wifi", "bluetooth", "gadget".  Only those technologies listed here are used for tethering.  If one wants to tether ethernet, then add "ethernet" in the list.  Note that if ethernet tethering is enabled, then a DHCP server is started on all ethernet interfaces.  Tethered ethernet should never be connected to corporate or home network as it will disrupt normal operation of these networks.  Due to this ethernet is not tethered by default.  Do not activate ethernet tethering unless you really know what you are doing.

     persistent-tethering-mode? (type: maybe-boolean)
          Restore earlier tethering status when returning from offline mode, re-enabling a technology, and after restarts and reboots.  Default value is #f.

     enable-6to4? (type: maybe-boolean)
          Automatically enable anycast 6to4 if possible.  This is not recommended, as the use of 6to4 will generally lead to a severe degradation of connection quality.  See RFC6343.  Default value is #f (as recommended by RFC6343 section 4.1).

     vendor-class-id (type: maybe-string)
          Set DHCP option 60 (Vendor Class ID) to the given string.  This option can be used by DHCP servers to identify specific clients without having to rely on MAC address ranges, etc.

     enable-online-check? (type: maybe-boolean)
          Enable or disable use of HTTP GET as an online status check.  When a service is in a READY state, and is selected as default, ConnMan will issue an HTTP GET request to verify that end-to-end connectivity is successful.  Only then the service will be transitioned to ONLINE state. If this setting is false, the default service will remain in READY state.  Default value is #t.

     online-check-ipv4-url (type: maybe-string)
          IPv4 URL used during the online status check.  Please refer to the README for more detailed information.  Default value is http://ipv4.connman.net/online/status.html.

     online-check-ipv6-url (type: maybe-string)
          IPv6 URL used during the online status check.  Please refer to the README for more detailed information.  Default value is http://ipv6.connman.net/online/status.html.

     online-check-initial-interval (type: maybe-number)
          Range of intervals between two online check requests.  Please refer to the README for more detailed information.  Default value is 1.

     online-check-max-interval (type: maybe-number)
          Range of intervals between two online check requests.  Please refer to the README for more detailed information.  Default value is 1.

     enable-online-to-ready-transition? (type: maybe-boolean)
          WARNING: This is an experimental feature.  In addition to enable-online-check setting, enable or disable use of HTTP GET to detect the loss of end-to-end connectivity.  If this setting is #f, when the default service transitions to ONLINE state, the HTTP GET request is no more called until next cycle, initiated by a transition of the default service to DISCONNECT state.  If this setting is #t, the HTTP GET request keeps being called to guarantee that end-to-end connectivity is still successful.  If not, the default service will transition to READY state, enabling another service to become the default one, in replacement.  Default value is #f.

     auto-connect-roaming-services? (type: maybe-boolean)
          Automatically connect roaming services.  This is not recommended unless you know you won't have any billing problem.  Default value is #f.

     address-conflict-detection? (type: maybe-boolean)
          Enable or disable the implementation of IPv4 address conflict detection according to RFC5227.  ConnMan will send probe ARP packets to see if an IPv4 address is already in use before assigning the address to an interface.  If an address conflict occurs for a statically configured address, an IPv4LL address will be chosen instead (according to RFC3927).  If an address conflict occurs for an address offered via DHCP, ConnMan sends a DHCP DECLINE once and for the second conflict resorts to finding an IPv4LL address.  Default value is #f.

     localtime (type: maybe-string)
          Path to localtime file.  Defaults to /etc/localtime.

     regulatory-domain-follows-timezone? (type: maybe-boolean)
          Enable regulatory domain to be changed along timezone changes.  With this option set to true each time the timezone changes the first present ISO3166 country code is read from /usr/share/zoneinfo/zone1970.tab and set as regulatory domain value.  Default value is #f.

     resolv-conf (type: maybe-string)
          Path to resolv.conf file.  If the file does not exist, but intermediate directories exist, it will be created.  If this option is not set, it tries to write into /var/run/connman/resolv.conf if it fails (/var/run/connman does not exist or is not writeable).  If you do not want to update resolv.conf, you can set /dev/null.

 -- Variable: wpa-supplicant-service-type
     This is the service type to run WPA supplicant (https://w1.fi/wpa_supplicant/), an authentication daemon required to authenticate against encrypted WiFi or ethernet networks.

 -- Data Type: wpa-supplicant-configuration
     Data type representing the configuration of WPA Supplicant.

     It takes the following parameters:

     wpa-supplicant (default: wpa-supplicant)
          The WPA Supplicant package to use.

     requirement (default: '(user-processes loopback syslogd)
          List of services that should be started before WPA Supplicant starts.

     dbus? (default: #t)
          Whether to listen for requests on D-Bus.

     pid-file (default: "/var/run/wpa_supplicant.pid")
          Where to store the PID file.

     interface (default: #f)
          If this is set, it must specify the name of a network interface that WPA supplicant will control.

     config-file (default: #f)
          Optional configuration file to use.

     extra-options (default: '())
          List of additional command-line arguments to pass to the daemon.

Some networking devices such as modems require special care, and this is what the services below focus on.

 -- Variable: modem-manager-service-type
     This is the service type for the ModemManager (https://wiki.gnome.org/Projects/ModemManager) service.  The value for this service type is a modem-manager-configuration record.

     This service is part of %desktop-services (see Desktop Services).

 -- Data Type: modem-manager-configuration
     Data type representing the configuration of ModemManager.

     modem-manager (default: modem-manager)
          The ModemManager package to use.

 -- Variable: usb-modeswitch-service-type
     This is the service type for the USB_ModeSwitch (https://www.draisberghof.de/usb_modeswitch/) service.  The value for this service type is a usb-modeswitch-configuration record.

     When plugged in, some USB modems (and other USB devices) initially present themselves as a read-only storage medium and not as a modem.  They need to be modeswitched before they are usable.  The USB_ModeSwitch service type installs udev rules to automatically modeswitch these devices when they are plugged in.

     This service is part of %desktop-services (see Desktop Services).

 -- Data Type: usb-modeswitch-configuration
     Data type representing the configuration of USB_ModeSwitch.

     usb-modeswitch (default: usb-modeswitch)
          The USB_ModeSwitch package providing the binaries for modeswitching.

     usb-modeswitch-data (default: usb-modeswitch-data)
          The package providing the device data and udev rules file used by USB_ModeSwitch.

     config-file (default: #~(string-append #$usb-modeswitch:dispatcher "/etc/usb_modeswitch.conf"))
          Which config file to use for the USB_ModeSwitch dispatcher.  By default the config file shipped with USB_ModeSwitch is used which disables logging to /var/log among other default settings.  If set to #f, no config file is used.

Networking Services
-------------------

The (gnu services networking) module discussed in the previous section provides services for more advanced setups: providing a DHCP service for others to use, filtering packets with iptables or nftables, running a WiFi access point with hostapd, running the inetd ``superdaemon'', and more.  This section describes those.

 -- Variable: dhcpd-service-type
     This type defines a service that runs a DHCP daemon.  To create a service of this type, you must supply a <dhcpd-configuration>. For example:

          (service dhcpd-service-type
                   (dhcpd-configuration
                    (config-file (local-file "my-dhcpd.conf"))
                    (interfaces '("enp0s25"))))

 -- Data Type: dhcpd-configuration

     package (default: isc-dhcp)
          The package that provides the DHCP daemon.  This package is expected to provide the daemon at sbin/dhcpd relative to its output directory.  The default package is the ISC's DHCP server (https://www.isc.org/dhcp/).

     config-file (default: #f)
          The configuration file to use.  This is required.  It will be passed to dhcpd via its -cf option.  This may be any ``file-like'' object (see file-like objects).  See man dhcpd.conf for details on the configuration file syntax.

     version (default: "4")
          The DHCP version to use.  The ISC DHCP server supports the values ``4'', ``6'', and ``4o6''.  These correspond to the dhcpd program options -4, -6, and -4o6.  See man dhcpd for details.

     run-directory (default: "/run/dhcpd")
          The run directory to use.  At service activation time, this directory will be created if it does not exist.

     pid-file (default: "/run/dhcpd/dhcpd.pid")
          The PID file to use.  This corresponds to the -pf option of dhcpd.  See man dhcpd for details.

     interfaces (default: '())
          The names of the network interfaces on which dhcpd should listen for broadcasts.  If this list is not empty, then its elements (which must be strings) will be appended to the dhcpd invocation when starting the daemon.  It may not be necessary to explicitly specify any interfaces here; see man dhcpd for details.

 -- Variable: hostapd-service-type
     This is the service type to run the hostapd (https://w1.fi/hostapd/) daemon to set up WiFi (IEEE 802.11) access points and authentication servers.  Its associated value must be a hostapd-configuration as shown below:

          ;; Use wlan1 to run the access point for "My Network".
          (service hostapd-service-type
                   (hostapd-configuration
                    (interface "wlan1")
                    (ssid "My Network")
                    (channel 12)))

 -- Data Type: hostapd-configuration
     This data type represents the configuration of the hostapd service, with the following fields:

     package (default: hostapd)
          The hostapd package to use.

     interface (default: "wlan0")
          The network interface to run the WiFi access point.

     ssid
          The SSID (service set identifier), a string that identifies this network.

     broadcast-ssid? (default: #t)
          Whether to broadcast this SSID.

     channel (default: 1)
          The WiFi channel to use.

     driver (default: "nl80211")
          The driver interface type.  "nl80211" is used with all Linux mac80211 drivers.  Use "none" if building hostapd as a standalone RADIUS server that does not control any wireless/wired driver.

     extra-settings (default: "")
          Extra settings to append as-is to the hostapd configuration file.  See https://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf for the configuration file reference.

 -- Variable: simulated-wifi-service-type
     This is the type of a service to simulate WiFi networking, which can be useful in virtual machines for testing purposes.  The service loads the Linux kernel mac80211_hwsim module (https://www.kernel.org/doc/html/latest/networking/mac80211_hwsim/mac80211_hwsim.html) and starts hostapd to create a pseudo WiFi network that can be seen on wlan0, by default.

     The service's value is a hostapd-configuration record.

 -- Variable: iptables-service-type
     This is the service type to set up an iptables configuration.  iptables is a packet filtering framework supported by the Linux kernel.  This service supports configuring iptables for both IPv4 and IPv6.  A simple example configuration rejecting all incoming connections except those to the ssh port 22 is shown below.

          (service iptables-service-type
                   (iptables-configuration
                    (ipv4-rules (plain-file "iptables.rules" "*filter
          :INPUT ACCEPT
          :FORWARD ACCEPT
          :OUTPUT ACCEPT
          -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
          -A INPUT -p tcp --dport 22 -j ACCEPT
          -A INPUT -j REJECT --reject-with icmp-port-unreachable
          COMMIT
          "))
                    (ipv6-rules (plain-file "ip6tables.rules" "*filter
          :INPUT ACCEPT
          :FORWARD ACCEPT
          :OUTPUT ACCEPT
          -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
          -A INPUT -p tcp --dport 22 -j ACCEPT
          -A INPUT -j REJECT --reject-with icmp6-port-unreachable
          COMMIT
          "))))

 -- Data Type: iptables-configuration
     The data type representing the configuration of iptables.

     iptables (default: iptables)
          The iptables package that provides iptables-restore and ip6tables-restore.

     ipv4-rules (default: %iptables-accept-all-rules)
          The iptables rules to use.  It will be passed to iptables-restore. This may be any ``file-like'' object (see file-like objects).

     ipv6-rules (default: %iptables-accept-all-rules)
          The ip6tables rules to use.  It will be passed to ip6tables-restore. This may be any ``file-like'' object (see file-like objects).

 -- Variable: nftables-service-type
     This is the service type to set up a nftables configuration.  nftables is a netfilter project that aims to replace the existing iptables, ip6tables, arptables and ebtables framework.  It provides a new packet filtering framework, a new user-space utility nft, and a compatibility layer for iptables.  This service comes with a default ruleset %default-nftables-ruleset that rejecting all incoming connections except those to the ssh port 22.  To use it, simply write:

          (service nftables-service-type)

 -- Data Type: nftables-configuration
     The data type representing the configuration of nftables.

     package (default: nftables)
          The nftables package that provides nft.

     ruleset (default: %default-nftables-ruleset)
          The nftables ruleset to use.  This may be any ``file-like'' object (see file-like objects).

 -- Variable: ntp-service-type
     This is the type of the service running the Network Time Protocol (NTP) (https://www.ntp.org) daemon, ntpd.  The daemon will keep the system clock synchronized with that of the specified NTP servers.

     The value of this service is an ntpd-configuration object, as described below.

 -- Data Type: ntp-configuration
     This is the data type for the NTP service configuration.

     servers (default: %ntp-servers)
          This is the list of servers (<ntp-server> records) with which ntpd will be synchronized.  See the ntp-server data type definition below.

     allow-large-adjustment? (default: #t)
          This determines whether ntpd is allowed to make an initial adjustment of more than 1,000 seconds.

     ntp (default: ntp)
          The NTP package to use.

 -- Variable: %ntp-servers
     List of host names used as the default NTP servers.  These are servers of the NTP Pool Project (https://www.ntppool.org/en/).

 -- Data Type: ntp-server
     The data type representing the configuration of a NTP server.

     type (default: 'server)
          The type of the NTP server, given as a symbol.  One of 'pool, 'server, 'peer, 'broadcast or 'manycastclient.

     address
          The address of the server, as a string.

     options
          NTPD options to use with that specific server, given as a list of option names and/or of option names and values tuples.  The following example define a server to use with the options iburst and prefer, as well as version 3 and a maxpoll time of 16 seconds.

               (ntp-server
                (type 'server)
                (address "some.ntp.server.org")
                (options `(iburst (version 3) (maxpoll 16) prefer))))

 -- Variable: openntpd-service-type
     Run the ntpd, the Network Time Protocol (NTP) daemon, as implemented by OpenNTPD (http://www.openntpd.org).  The daemon will keep the system clock synchronized with that of the given servers.

          (service
           openntpd-service-type
           (openntpd-configuration
            (listen-on '("127.0.0.1" "::1"))
            (sensor '("udcf0 correction 70000"))
            (constraint-from '("www.gnu.org"))
            (constraints-from '("https://www.google.com/"))))

 -- Variable: %openntpd-servers
     This variable is a list of the server addresses defined in %ntp-servers.

 -- Data Type: openntpd-configuration

     openntpd (default: openntpd)
          The openntpd package to use.

     listen-on (default: '("127.0.0.1" "::1"))
          A list of local IP addresses or hostnames the ntpd daemon should listen on.

     query-from (default: '())
          A list of local IP address the ntpd daemon should use for outgoing queries.

     sensor (default: '())
          Specify a list of timedelta sensor devices ntpd should use.  ntpd will listen to each sensor that actually exists and ignore non-existent ones. See upstream documentation (https://man.openbsd.org/ntpd.conf) for more information.

     server (default: '())
          Specify a list of IP addresses or hostnames of NTP servers to synchronize to.

     servers (default: %openntp-servers)
          Specify a list of IP addresses or hostnames of NTP pools to synchronize to.

     constraint-from (default: '())
          ntpd can be configured to query the ‘Date’ from trusted HTTPS servers via TLS. This time information is not used for precision but acts as an authenticated constraint, thereby reducing the impact of unauthenticated NTP man-in-the-middle attacks. Specify a list of URLs, IP addresses or hostnames of HTTPS servers to provide a constraint.

     constraints-from (default: '())
          As with constraint from, specify a list of URLs, IP addresses or hostnames of HTTPS servers to provide a constraint.  Should the hostname resolve to multiple IP addresses, ntpd will calculate a median constraint from all of them.

 -- Variable: inetd-service-type
     This service runs the inetd (see inetd invocation (GNU Inetutils)) daemon.  inetd listens for connections on internet sockets, and lazily starts the specified server program when a connection is made on one of these sockets.

     The value of this service is an inetd-configuration object.  The following example configures the inetd daemon to provide the built-in echo service, as well as an smtp service which forwards smtp traffic over ssh to a server smtp-server behind a gateway hostname:

          (service
           inetd-service-type
           (inetd-configuration
            (entries (list
                      (inetd-entry
                       (name "echo")
                       (socket-type 'stream)
                       (protocol "tcp")
                       (wait? #f)
                       (user "root"))
                      (inetd-entry
                       (node "127.0.0.1")
                       (name "smtp")
                       (socket-type 'stream)
                       (protocol "tcp")
                       (wait? #f)
                       (user "root")
                       (program (file-append openssh "/bin/ssh"))
                       (arguments
                        '("ssh" "-qT" "-i" "/path/to/ssh_key"
                          "-W" "smtp-server:25" "user@hostname")))))))

     See below for more details about inetd-configuration.

 -- Data Type: inetd-configuration
     Data type representing the configuration of inetd.

     program (default: (file-append inetutils "/libexec/inetd"))
          The inetd executable to use.

     entries (default: '())
          A list of inetd service entries.  Each entry should be created by the inetd-entry constructor.

 -- Data Type: inetd-entry
     Data type representing an entry in the inetd configuration. Each entry corresponds to a socket where inetd will listen for requests.

     node (default: #f)
          Optional string, a comma-separated list of local addresses inetd should use when listening for this service. See Configuration file (GNU Inetutils) for a complete description of all options.

     name
          A string, the name must correspond to an entry in /etc/services.

     socket-type
          One of 'stream, 'dgram, 'raw, 'rdm or 'seqpacket.

     protocol
          A string, must correspond to an entry in /etc/protocols.

     wait? (default: #t)
          Whether inetd should wait for the server to exit before listening to new service requests.

     user
          A string containing the user (and, optionally, group) name of the user as whom the server should run.  The group name can be specified in a suffix, separated by a colon or period, i.e. "user", "user:group" or "user.group".

     program (default: "internal")
          The server program which will serve the requests, or "internal" if inetd should use a built-in service.

     arguments (default: '())
          A list strings or file-like objects, which are the server program's arguments, starting with the zeroth argument, i.e. the name of the program itself.  For inetd's internal services, this entry must be '() or '("internal").

     See Configuration file (GNU Inetutils) for a more detailed discussion of each configuration field.

 -- Variable: opendht-service-type
     This is the type of the service running a OpenDHT (https://opendht.net) node, dhtnode.  The daemon can be used to host your own proxy service to the distributed hash table (DHT), for example to connect to with Jami, among other applications.

          When using the OpenDHT proxy server, the IP addresses it ``sees'' from the clients should be addresses reachable from other peers.  In practice this means that a publicly reachable address is best suited for a proxy server, outside of your private network.  For example, hosting the proxy server on a IPv4 private local network and exposing it via port forwarding could work for external peers, but peers local to the proxy would have their private addresses shared with the external peers, leading to connectivity problems.

     The value of this service is a opendht-configuration object, as described below.

 -- Data Type: opendht-configuration
     Available opendht-configuration fields are:

     opendht (default: opendht) (type: file-like)
          The opendht package to use.

     peer-discovery? (default: #f) (type: boolean)
          Whether to enable the multicast local peer discovery mechanism.

     enable-logging? (default: #f) (type: boolean)
          Whether to enable logging messages to syslog.  It is disabled by default as it is rather verbose.

     debug? (default: #f) (type: boolean)
          Whether to enable debug-level logging messages.  This has no effect if logging is disabled.

     bootstrap-host (default: "bootstrap.jami.net:4222") (type: maybe-string)
          The node host name that is used to make the first connection to the network.  A specific port value can be provided by appending the :PORT suffix.  By default, it uses the Jami bootstrap nodes, but any host can be specified here.  It's also possible to disable bootstrapping by explicitly setting this field to the %unset-value value.

     port (default: 4222) (type: maybe-number)
          The UDP port to bind to.  When left unspecified, an available port is automatically selected.

     proxy-server-port (type: maybe-number)
          Spawn a proxy server listening on the specified port.

     proxy-server-port-tls (type: maybe-number)
          Spawn a proxy server listening to TLS connections on the specified port.

 -- Variable: tor-service-type
     Type for a service that runs the Tor (https://torproject.org) anonymous networking daemon.  The service is configured using a <tor-configuration> record.  By default, the Tor daemon runs as the tor unprivileged user, which is a member of the tor group.

     Services of this type can be extended by other services to specify onion services (in addition to those already specified in tor-configuration) as in this example:

          (simple-service 'my-extra-onion-service tor-service-type
                          (list (tor-onion-service-configuration
                                  (name "extra-onion-service")
                                  (mapping '((80 . "127.0.0.1:8080"))))))

 -- Data Type: tor-configuration

     tor (default: tor)
          The package that provides the Tor daemon.  This package is expected to provide the daemon at bin/tor relative to its output directory.  The default package is the Tor Project's (https://www.torproject.org) implementation.

     config-file (default: (plain-file "empty" ""))
          The configuration file to use.  It will be appended to a default configuration file, and the final configuration file will be passed to tor via its -f option.  This may be any ``file-like'' object (see file-like objects).  See man tor for details on the configuration file syntax.

     hidden-services (default: '())
          The list of <tor-onion-service-configuration> records to use. For any onion service you include in this list, appropriate configuration to enable the onion service will be automatically added to the default configuration file.

     socks-socket-type (default: 'tcp)
          The default socket type that Tor should use for its SOCKS socket.  This must be either 'tcp or 'unix.  If it is 'tcp, then by default Tor will listen on TCP port 9050 on the loopback interface (i.e., localhost). If it is 'unix, then Tor will listen on the UNIX domain socket /var/run/tor/socks-sock, which will be made writable by members of the tor group.

          If you want to customize the SOCKS socket in more detail, leave socks-socket-type at its default value of 'tcp and use config-file to override the default by providing your own SocksPort option.

     control-socket? (default: #f)
          Whether or not to provide a ``control socket'' by which Tor can be controlled to, for instance, dynamically instantiate tor onion services. If #t, Tor will listen for control commands on the UNIX domain socket /var/run/tor/control-sock, which will be made writable by members of the tor group.

 -- Data Type: tor-onion-service-configuration
     Data Type representing a Tor Onion Service configuration. See the Tor project's documentation (https://community.torproject.org/onion-services/) for more information. Available tor-onion-service-configuration fields are:

     name (type: string)
          Name for this Onion Service.  This creates a /var/lib/tor/hidden-services/NAME directory, where the hostname file contains the .onion host name for this Onion Service.

     mapping (type: alist)
          Association list of port to address mappings.  The following example:

               '((22 . "127.0.0.1:22")
                 (80 . "127.0.0.1:8080"))

          maps ports 22 and 80 of the Onion Service to the local ports 22 and 8080.

The (gnu services rsync) module provides the following services:

You might want an rsync daemon if you have files that you want available so anyone (or just yourself) can download existing files or upload new files.

 -- Variable: rsync-service-type
     This is the service type for the rsync (https://rsync.samba.org) daemon, The value for this service type is a rsync-configuration record as in this example:

          ;; Export two directories over rsync.  By default rsync listens on
          ;; all the network interfaces.
          (service rsync-service-type
                   (rsync-configuration
                     (modules (list (rsync-module
                                      (name "music")
                                      (file-name "/srv/zik")
                                      (read-only? #f))
                                    (rsync-module
                                      (name "movies")
                                      (file-name "/home/charlie/movies"))))))

     See below for details about rsync-configuration.

 -- Data Type: rsync-configuration
     Data type representing the configuration for rsync-service.

     package (default: RSYNC)
          rsync package to use.

     address (default: #f)
          IP address on which rsync listens for incoming connections. If unspecified, it defaults to listening on all available addresses.

     port-number (default: 873)
          TCP port on which rsync listens for incoming connections.  If port is less than 1024 rsync needs to be started as the root user and group.

     pid-file (default: "/var/run/rsyncd/rsyncd.pid")
          Name of the file where rsync writes its PID.

     lock-file (default: "/var/run/rsyncd/rsyncd.lock")
          Name of the file where rsync writes its lock file.

     log-file (default: "/var/log/rsyncd.log")
          Name of the file where rsync writes its log file.

     user (default: "root")
          Owner of the rsync process.

     group (default: "root")
          Group of the rsync process.

     uid (default: "rsyncd")
          User name or user ID that file transfers to and from that module should take place as when the daemon was run as root.

     gid (default: "rsyncd")
          Group name or group ID that will be used when accessing the module.

     modules (default: %default-modules)
          List of ``modules''---i.e., directories exported over rsync.  Each element must be a rsync-module record, as described below.

 -- Data Type: rsync-module
     This is the data type for rsync ``modules''.  A module is a directory exported over the rsync protocol.  The available fields are as follows:

     name
          The module name.  This is the name that shows up in URLs.  For example, if the module is called music, the corresponding URL will be rsync://host.example.org/music.

     file-name
          Name of the directory being exported.

     comment (default: "")
          Comment associated with the module.  Client user interfaces may display it when they obtain the list of available modules.

     read-only? (default: #t)
          Whether or not client will be able to upload files.  If this is false, the uploads will be authorized if permissions on the daemon side permit it.

     chroot? (default: #t)
          When this is true, the rsync daemon changes root to the module's directory before starting file transfers with the client.  This improves security, but requires rsync to run as root.

     timeout (default: 300)
          Idle time in seconds after which the daemon closes a connection with the client.

The (gnu services syncthing) module provides the following services:

You might want a syncthing daemon if you have files between two or more computers and want to sync them in real time, safely protected from prying eyes.

 -- Variable: syncthing-service-type
     This is the service type for the syncthing (https://syncthing.net/) daemon, The value for this service type is a syncthing-configuration record as in this example:

          (service syncthing-service-type
                   (syncthing-configuration (user "alice")))

          This service is also available for Guix Home, where it runs directly with your user privileges (see home-syncthing-service-type).

     See below for details about syncthing-configuration.

 -- Data Type: syncthing-configuration
     Data type representing the configuration for syncthing-service-type.

     syncthing (default: SYNCTHING)
          syncthing package to use.

     arguments (default: '())
          List of command-line arguments passing to syncthing binary.

     logflags (default: 0)
          Sum of logging flags, see Syncthing documentation logflags (https://docs.syncthing.net/users/syncthing.html#cmdoption-logflags).

     user (default: #F)
          The user as which the Syncthing service is to be run. This assumes that the specified user exists.

     group (default: "USERS")
          The group as which the Syncthing service is to be run. This assumes that the specified group exists.

     home (default: #F)
          Common configuration and data directory.  The default configuration directory is $HOME of the specified Syncthing user.

Furthermore, (gnu services ssh) provides the following services.

 -- Variable: lsh-service-type
     Type of the service that runs the GNU lsh secure shell (SSH) daemon, lshd.  The value for this service is a <lsh-configuration> object.

 -- Data Type: lsh-configuration
     Data type representing the configuration of lshd.

     lsh (default: lsh) (type: file-like)
          The package object of the GNU lsh secure shell (SSH) daemon.

     daemonic? (default: #t) (type: boolean)
          Whether to detach from the controlling terminal.

     host-key (default: "/etc/lsh/host-key") (type: string)
          File containing the host key.  This file must be readable by root only.

     interfaces (default: '()) (type: list)
          List of host names or addresses that lshd will listen on. If empty, lshd listens for connections on all the network interfaces.

     port-number (default: 22) (type: integer)
          Port to listen on.

     allow-empty-passwords? (default: #f) (type: boolean)
          Whether to accept log-ins with empty passwords.

     root-login? (default: #f) (type: boolean)
          Whether to accept log-ins as root.

     syslog-output? (default: #t) (type: boolean)
          Whether to log lshd standard output to syslogd. This will make the service depend on the existence of a syslogd service.

     pid-file? (default: #f) (type: boolean)
          When #t, lshd writes its PID to the file specified in PID-FILE.

     pid-file (default: "/var/run/lshd.pid") (type: string)
          File that lshd will write its PID to.

     x11-forwarding? (default: #t) (type: boolean)
          Whether to enable X11 forwarding.

     tcp/ip-forwarding? (default: #t) (type: boolean)
          Whether to enable TCP/IP forwarding.

     password-authentication? (default: #t) (type: boolean)
          Whether to accept log-ins using password authentication.

     public-key-authentication? (default: #t) (type: boolean)
          Whether to accept log-ins using public key authentication.

     initialize? (default: #t) (type: boolean)
          When #f, it is up to the user to initialize the randomness generator (see lsh-make-seed (LSH Manual)), and to create a key pair with the private key stored in file HOST-KEY (see lshd basics (LSH Manual)).

 -- Variable: openssh-service-type
     This is the type for the OpenSSH (http://www.openssh.org) secure shell daemon, sshd.  Its value must be an openssh-configuration record as in this example:

          (service openssh-service-type
                   (openssh-configuration
                     (x11-forwarding? #t)
                     (permit-root-login 'prohibit-password)
                     (authorized-keys
                       `(("alice" ,(local-file "alice.pub"))
                         ("bob" ,(local-file "bob.pub"))))))

     See below for details about openssh-configuration.

     This service can be extended with extra authorized keys, as in this example:

          (service-extension openssh-service-type
                             (const `(("charlie"
                                       ,(local-file "charlie.pub")))))

 -- Data Type: openssh-configuration
     This is the configuration record for OpenSSH's sshd.

     openssh (default OPENSSH)
          The OpenSSH package to use.

     pid-file (default: "/var/run/sshd.pid")
          Name of the file where sshd writes its PID.

     port-number (default: 22)
          TCP port on which sshd listens for incoming connections.

     max-connections (default: 200)
          Hard limit on the maximum number of simultaneous client connections, enforced by the inetd-style Shepherd service (see make-inetd-constructor (The GNU Shepherd Manual)).

     permit-root-login (default: #f)
          This field determines whether and when to allow logins as root.  If #f, root logins are disallowed; if #t, they are allowed. If it's the symbol 'prohibit-password, then root logins are permitted but not with password-based authentication.

     allow-empty-passwords? (default: #f)
          When true, users with empty passwords may log in.  When false, they may not.

     password-authentication? (default: #t)
          When true, users may log in with their password.  When false, they have other authentication methods.

     public-key-authentication? (default: #t)
          When true, users may log in using public key authentication.  When false, users have to use other authentication method.

          Authorized public keys are stored in ~/.ssh/authorized_keys. This is used only by protocol version 2.

     x11-forwarding? (default: #f)
          When true, forwarding of X11 graphical client connections is enabled---in other words, ssh options -X and -Y will work.

     allow-agent-forwarding? (default: #t)
          Whether to allow agent forwarding.

     allow-tcp-forwarding? (default: #t)
          Whether to allow TCP forwarding.

     gateway-ports? (default: #f)
          Whether to allow gateway ports.

     challenge-response-authentication? (default: #f)
          Specifies whether challenge response authentication is allowed (e.g. via PAM).

     use-pam? (default: #t)
          Enables the Pluggable Authentication Module interface.  If set to #t, this will enable PAM authentication using challenge-response-authentication? and password-authentication?, in addition to PAM account and session module processing for all authentication types.

          Because PAM challenge response authentication usually serves an equivalent role to password authentication, you should disable either challenge-response-authentication? or password-authentication?.

     print-last-log? (default: #t)
          Specifies whether sshd should print the date and time of the last user login when a user logs in interactively.

     subsystems (default: '(("sftp" "internal-sftp")))
          Configures external subsystems (e.g. file transfer daemon).

          This is a list of two-element lists, each of which containing the subsystem name and a command (with optional arguments) to execute upon subsystem request.

          The command internal-sftp implements an in-process SFTP server.  Alternatively, one can specify the sftp-server command:

               (service openssh-service-type
                        (openssh-configuration
                         (subsystems
                          `(("sftp" ,(file-append openssh "/libexec/sftp-server"))))))

     accepted-environment (default: '())
          List of strings describing which environment variables may be exported.

          Each string gets on its own line.  See the AcceptEnv option in man sshd_config.

          This example allows ssh-clients to export the COLORTERM variable. It is set by terminal emulators, which support colors.  You can use it in your shell's resource file to enable colors for the prompt and commands if this variable is set.

               (service openssh-service-type
                        (openssh-configuration
                          (accepted-environment '("COLORTERM"))))

     authorized-keys (default: '())
          This is the list of authorized keys.  Each element of the list is a user name followed by one or more file-like objects that represent SSH public keys.  For example:

               (openssh-configuration
                 (authorized-keys
                   `(("rekado" ,(local-file "rekado.pub"))
                     ("chris" ,(local-file "chris.pub"))
                     ("root" ,(local-file "rekado.pub") ,(local-file "chris.pub")))))

          registers the specified public keys for user accounts rekado, chris, and root.

          Additional authorized keys can be specified via service-extension.

          Note that this does not interfere with the use of ~/.ssh/authorized_keys.

     generate-host-keys? (default: #t)
          Whether to generate host key pairs with ssh-keygen -A under /etc/ssh if there are none.

          Generating key pairs takes a few seconds when enough entropy is available and is only done once.  You might want to turn it off for instance in a virtual machine that does not need it because host keys are provided in some other way, and where the extra boot time is a problem.

     log-level (default: 'info)
          This is a symbol specifying the logging level: quiet, fatal, error, info, verbose, debug, etc.  See the man page for sshd_config for the full list of level names.

     extra-content (default: "")
          This field can be used to append arbitrary text to the configuration file.  It is especially useful for elaborate configurations that cannot be expressed otherwise.  This configuration, for example, would generally disable root logins, but permit them from one specific IP address:

               (openssh-configuration
                 (extra-content "\
               Match Address 192.168.0.1
                 PermitRootLogin yes"))

 -- Variable: dropbear-service-type
     Type of the service that runs the Dropbear SSH daemon (https://matt.ucc.asn.au/dropbear/dropbear.html), whose value is a <dropbear-configuration> object.

     For example, to specify a Dropbear service listening on port 1234:

          (service dropbear-service-type (dropbear-configuration
                                           (port-number 1234)))

 -- Data Type: dropbear-configuration
     This data type represents the configuration of a Dropbear SSH daemon.

     dropbear (default: DROPBEAR)
          The Dropbear package to use.

     port-number (default: 22)
          The TCP port where the daemon waits for incoming connections.

     syslog-output? (default: #t)
          Whether to enable syslog output.

     pid-file (default: "/var/run/dropbear.pid")
          File name of the daemon's PID file.

     root-login? (default: #f)
          Whether to allow root logins.

     allow-empty-passwords? (default: #f)
          Whether to allow empty passwords.

     password-authentication? (default: #t)
          Whether to enable password-based authentication.

 -- Variable: autossh-service-type
     This is the type for the AutoSSH (https://www.harding.motd.ca/autossh) program that runs a copy of ssh and monitors it, restarting it as necessary should it die or stop passing traffic. AutoSSH can be run manually from the command-line by passing arguments to the binary autossh from the package autossh, but it can also be run as a Guix service.  This latter use case is documented here.

     AutoSSH can be used to forward local traffic to a remote machine using an SSH tunnel, and it respects the ~/.ssh/config of the user it is run as.

     For example, to specify a service running autossh as the user pino and forwarding all local connections to port 8081 to remote:8081 using an SSH tunnel, add this call to the operating system's services field:

          (service autossh-service-type
                   (autossh-configuration
                    (user "pino")
                    (ssh-options (list "-T" "-N" "-L" "8081:localhost:8081" "remote.net"))))

 -- Data Type: autossh-configuration
     This data type represents the configuration of an AutoSSH service.

     user (default "autossh")
          The user as which the AutoSSH service is to be run. This assumes that the specified user exists.

     poll (default 600)
          Specifies the connection poll time in seconds.

     first-poll (default #f)
          Specifies how many seconds AutoSSH waits before the first connection test.  After this first test, polling is resumed at the pace defined in poll.  When set to #f, the first poll is not treated specially and will also use the connection poll specified in poll.

     gate-time (default 30)
          Specifies how many seconds an SSH connection must be active before it is considered successful.

     log-level (default 1)
          The log level, corresponding to the levels used by syslog---so 0 is the most silent while 7 is the chattiest.

     max-start (default #f)
          The maximum number of times SSH may be (re)started before AutoSSH exits. When set to #f, no maximum is configured and AutoSSH may restart indefinitely.

     message (default "")
          The message to append to the echo message sent when testing connections.

     port (default "0")
          The ports used for monitoring the connection.  When set to "0", monitoring is disabled.  When set to "N" where N is a positive integer, ports N and N+1 are used for monitoring the connection, such that port N is the base monitoring port and n+1 is the echo port.  When set to "N:M" where N and M are positive integers, the ports N and M are used for monitoring the connection, such that port N is the base monitoring port and M is the echo port.

     ssh-options (default '())
          The list of command-line arguments to pass to ssh when it is run.  Options -f and -M are reserved for AutoSSH and may cause undefined behaviour.

 -- Variable: webssh-service-type
     This is the type for the WebSSH (https://webssh.huashengdun.org/) program that runs a web SSH client.  WebSSH can be run manually from the command-line by passing arguments to the binary wssh from the package webssh, but it can also be run as a Guix service.  This latter use case is documented here.

     For example, to specify a service running WebSSH on loopback interface on port 8888 with reject policy with a list of allowed to connection hosts, and NGINX as a reverse-proxy to this service listening for HTTPS connection, add this call to the operating system's services field:

          (service webssh-service-type
            (webssh-configuration (address "127.0.0.1")
                                  (port 8888)
                                  (policy 'reject)
                                  (known-hosts '("localhost ecdsa-sha2-nistp256 AAAA…"
                                                 "127.0.0.1 ecdsa-sha2-nistp256 AAAA…"))))

          (service nginx-service-type
                   (nginx-configuration
                    (server-blocks
                     (list
                      (nginx-server-configuration
                       (inherit %webssh-configuration-nginx)
                       (server-name '("webssh.example.com"))
                       (listen '("443 ssl"))
                       (ssl-certificate (letsencrypt-certificate "webssh.example.com"))
                       (ssl-certificate-key (letsencrypt-key "webssh.example.com"))
                       (locations
                        (cons (nginx-location-configuration
                               (uri "/.well-known")
                               (body '("root /var/www;")))
                              (nginx-server-configuration-locations %webssh-configuration-nginx))))))))

 -- Data Type: webssh-configuration
     Data type representing the configuration for webssh-service.

     package (default: WEBSSH)
          webssh package to use.

     user-name (default: "WEBSSH")
          User name or user ID that file transfers to and from that module should take place.

     group-name (default: "WEBSSH")
          Group name or group ID that will be used when accessing the module.

     address (default: #F)
          IP address on which webssh listens for incoming connections.

     port (default: 8888)
          TCP port on which webssh listens for incoming connections.

     policy (default: #F)
          Connection policy.  REJECT policy requires to specify KNOWN-HOSTS.

     known-hosts (default: '())
          List of hosts which allowed for SSH connection from webssh.

     log-file (default: "/var/log/webssh.log")
          Name of the file where webssh writes its log file.

     log-level (default: #F)
          Logging level.

 -- Variable: block-facebook-hosts-service-type
     This service type adds a list of known Facebook hosts to the /etc/hosts file. (see Host Names (The GNU C Library Reference Manual)) Each line contains a entry that maps a known server name of the Facebook on-line service---e.g., www.facebook.com---to the local host---127.0.0.1 or its IPv6 equivalent, ::1.

     This mechanism can prevent programs running locally, such as Web browsers, from accessing Facebook.

The (gnu services avahi) provides the following definition.

 -- Variable: avahi-service-type
     This is the service that runs avahi-daemon, a system-wide mDNS/DNS-SD responder that allows for service discovery and ``zero-configuration'' host name lookups (see https://avahi.org/). Its value must be an avahi-configuration record---see below.

     This service extends the name service cache daemon (nscd) so that it can resolve .local host names using nss-mdns (https://0pointer.de/lennart/projects/nss-mdns/).  See Name Service Switch, for information on host name resolution.

     Additionally, add the AVAHI package to the system profile so that commands such as avahi-browse are directly usable.

 -- Data Type: avahi-configuration
     Data type representation the configuration for Avahi.

     host-name (default: #f)
          If different from #f, use that as the host name to publish for this machine; otherwise, use the machine's actual host name.

     publish? (default: #t)
          When true, allow host names and services to be published (broadcast) over the network.

     publish-workstation? (default: #t)
          When true, avahi-daemon publishes the machine's host name and IP address via mDNS on the local network.  To view the host names published on your local network, you can run:

               avahi-browse _workstation._tcp

     wide-area? (default: #f)
          When true, DNS-SD over unicast DNS is enabled.

     ipv4? (default: #t)
     ipv6? (default: #t)
          These fields determine whether to use IPv4/IPv6 sockets.

     domains-to-browse (default: '())
          This is a list of domains to browse.

 -- Variable: openvswitch-service-type
     This is the type of the Open vSwitch (https://www.openvswitch.org) service, whose value should be an openvswitch-configuration object.

 -- Data Type: openvswitch-configuration
     Data type representing the configuration of Open vSwitch, a multilayer virtual switch which is designed to enable massive network automation through programmatic extension.

     package (default: OPENVSWITCH)
          Package object of the Open vSwitch.

 -- Variable: pagekite-service-type
     This is the service type for the PageKite (https://pagekite.net) service, a tunneling solution for making localhost servers publicly visible, even from behind restrictive firewalls or NAT without forwarded ports.  The value for this service type is a pagekite-configuration record.

     Here's an example exposing the local HTTP and SSH daemons:

          (service pagekite-service-type
                   (pagekite-configuration
                     (kites '("http:@kitename:localhost:80:@kitesecret"
                              "raw/22:@kitename:localhost:22:@kitesecret"))
                     (extra-file "/etc/pagekite.rc")))

 -- Data Type: pagekite-configuration
     Data type representing the configuration of PageKite.

     package (default: PAGEKITE)
          Package object of PageKite.

     kitename (default: #f)
          PageKite name for authenticating to the frontend server.

     kitesecret (default: #f)
          Shared secret for authenticating to the frontend server.  You should probably put this inside extra-file instead.

     frontend (default: #f)
          Connect to the named PageKite frontend server instead of the pagekite.net service.

     kites (default: '("http:@kitename:localhost:80:@kitesecret"))
          List of service kites to use.  Exposes HTTP on port 80 by default.  The format is proto:kitename:host:port:secret.

     extra-file (default: #f)
          Extra configuration file to read, which you are expected to create manually. Use this to add additional options and manage shared secrets out-of-band.

 -- Variable: yggdrasil-service-type
     The service type for connecting to the Yggdrasil network (https://yggdrasil-network.github.io/), an early-stage implementation of a fully end-to-end encrypted IPv6 network.

          Yggdrasil provides name-independent routing with cryptographically generated addresses.  Static addressing means you can keep the same address as long as you want, even if you move to a new location, or generate a new address (by generating new keys) whenever you want. https://yggdrasil-network.github.io/2018/07/28/addressing.html

     Pass it a value of yggdrasil-configuration to connect it to public peers and/or local peers.

     Here is an example using public peers and a static address.  The static signing and encryption keys are defined in /etc/yggdrasil-private.conf (the default value for config-file).

          ;; part of the operating-system declaration
          (service yggdrasil-service-type
                        (yggdrasil-configuration
                         (autoconf? #f) ;; use only the public peers
                         (json-config
                         ;; choose one from
                         ;; https://github.com/yggdrasil-network/public-peers
                          '((peers . #("tcp://1.2.3.4:1337"))))
                         ;; /etc/yggdrasil-private.conf is the default value for config-file
                         ))

          # sample content for /etc/yggdrasil-private.conf
          {
            # Your private key. DO NOT share this with anyone!
            PrivateKey: 5c750...
          }

 -- Data Type: yggdrasil-configuration
     Data type representing the configuration of Yggdrasil.

     package (default: yggdrasil)
          Package object of Yggdrasil.

     json-config (default: '())
          Contents of /etc/yggdrasil.conf.  Will be merged with /etc/yggdrasil-private.conf.  Note that these settings are stored in the Guix store, which is readable to all users. Do not store your private keys in it.  See the output of yggdrasil -genconf for a quick overview of valid keys and their default values.

     autoconf? (default: #f)
          Whether to use automatic mode.  Enabling it makes Yggdrasil use a dynamic IP and peer with IPv6 neighbors.

     log-level (default: 'info)
          How much detail to include in logs.  Use 'debug for more detail.

     log-to (default: 'stdout)
          Where to send logs.  By default, the service logs standard output to /var/log/yggdrasil.log.  The alternative is 'syslog, which sends output to the running syslog service.

     config-file (default: "/etc/yggdrasil-private.conf")
          What HJSON file to load sensitive data from.  This is where private keys should be stored, which are necessary to specify if you don't want a randomized address after each restart.  Use #f to disable.  Options defined in this file take precedence over json-config.  Use the output of yggdrasil -genconf as a starting point.  To configure a static address, delete everything except PrivateKey option.

 -- Variable: ipfs-service-type
     The service type for connecting to the IPFS network (https://ipfs.io), a global, versioned, peer-to-peer file system. Pass it a ipfs-configuration to change the ports used for the gateway and API.

     Here's an example configuration, using some non-standard ports:

          (service ipfs-service-type
                   (ipfs-configuration
                    (gateway "/ip4/127.0.0.1/tcp/8880")
                    (api "/ip4/127.0.0.1/tcp/8881")))

 -- Data Type: ipfs-configuration
     Data type representing the configuration of IPFS.

     package (default: go-ipfs)
          Package object of IPFS.

     gateway (default: "/ip4/127.0.0.1/tcp/8082")
          Address of the gateway, in ‘multiaddress’ format.

     api (default: "/ip4/127.0.0.1/tcp/5001")
          Address of the API endpoint, in ‘multiaddress’ format.

 -- Variable: keepalived-service-type
     This is the type for the Keepalived (https://www.keepalived.org/) routing software, keepalived.  Its value must be an keepalived-configuration record as in this example for master machine:

          (service keepalived-service-type
                   (keepalived-configuration
                     (config-file (local-file "keepalived-master.conf"))))

     where keepalived-master.conf:

          vrrp_instance my-group {
            state MASTER
            interface enp9s0
            virtual_router_id 100
            priority 100
            unicast_peer { 10.0.0.2 }
            virtual_ipaddress {
              10.0.0.4/24
            }
          }

     and for backup machine:

          (service keepalived-service-type
                   (keepalived-configuration
                    (config-file (local-file "keepalived-backup.conf"))))

     where keepalived-backup.conf:

          vrrp_instance my-group {
            state BACKUP
            interface enp9s0
            virtual_router_id 100
            priority 99
            unicast_peer { 10.0.0.3 }
            virtual_ipaddress {
              10.0.0.4/24
            }
          }

Unattended Upgrades
-------------------

Guix provides a service to perform unattended upgrades: periodically, the system automatically reconfigures itself from the latest Guix.  Guix System has several properties that make unattended upgrades safe:

  * upgrades are transactional (either the upgrade succeeds or it fails, but you cannot end up with an ``in-between'' system state);

  * the upgrade log is kept---you can view it with guix system list-generations---and you can roll back to any previous generation, should the upgraded system fail to behave as intended;

  * channel code is authenticated so you know you can only run genuine code (see Channels);

  * guix system reconfigure prevents downgrades, which makes it immune to downgrade attacks.

To set up unattended upgrades, add an instance of unattended-upgrade-service-type like the one below to the list of your operating system services:

     (service unattended-upgrade-service-type)

The defaults above set up weekly upgrades: every Sunday at midnight. You do not need to provide the operating system configuration file: it uses /run/current-system/configuration.scm, which ensures it always uses your latest configuration---see provenance-service-type, for more information about this file.

There are several things that can be configured, in particular the periodicity and services (daemons) to be restarted upon completion. When the upgrade is successful, the service takes care of deleting system generations older that some threshold, as per guix system delete-generations.  See the reference below for details.

To ensure that upgrades are actually happening, you can run guix system describe.  To investigate upgrade failures, visit the unattended upgrade log file (see below).

 -- Variable: unattended-upgrade-service-type
     This is the service type for unattended upgrades.  It sets up an mcron job (see Scheduled Job Execution) that runs guix system reconfigure from the latest version of the specified channels.

     Its value must be a unattended-upgrade-configuration record (see below).

 -- Data Type: unattended-upgrade-configuration
     This data type represents the configuration of the unattended upgrade service.  The following fields are available:

     schedule (default: "30 01 * * 0")
          This is the schedule of upgrades, expressed as a gexp containing an mcron job schedule (see mcron job specifications (GNU mcron)).

     channels (default: #~%default-channels)
          This gexp specifies the channels to use for the upgrade (see Channels).  By default, the tip of the official guix channel is used.

     operating-system-file (default: "/run/current-system/configuration.scm")
          This field specifies the operating system configuration file to use. The default is to reuse the config file of the current configuration.

          There are cases, though, where referring to /run/current-system/configuration.scm is not enough, for instance because that file refers to extra files (SSH public keys, extra configuration files, etc.) via local-file and similar constructs.  For those cases, we recommend something along these lines:

               (unattended-upgrade-configuration
                 (operating-system-file
                   (file-append (local-file "." "config-dir" #:recursive? #t)
                                "/config.scm")))

          The effect here is to import all of the current directory into the store, and to refer to config.scm within that directory. Therefore, uses of local-file within config.scm will work as expected.  See G-Expressions, for information about local-file and file-append.

     operating-system-expression (default: #f)
          This field specifies an expression that evaluates to the operating system to use for the upgrade.  If no value is provided the operating-system-file field value is used.

               (unattended-upgrade-configuration
                 (operating-system-expression
                   #~(@ (guix system install) installation-os)))

     services-to-restart (default: '(mcron))
          This field specifies the Shepherd services to restart when the upgrade completes.

          Those services are restarted right away upon completion, as with herd restart, which ensures that the latest version is running---remember that by default guix system reconfigure only restarts services that are not currently running, which is conservative: it minimizes disruption but leaves outdated services running.

          Use herd status to find out candidates for restarting. See Services, for general information about services.  Common services to restart would include ntpd and ssh-daemon.

          By default, the mcron service is restarted.  This ensures that the latest version of the unattended upgrade job will be used next time.

     system-expiration (default: (* 3 30 24 3600))
          This is the expiration time in seconds for system generations.  System generations older that this amount of time are deleted with guix system delete-generations when an upgrade completes.

               The unattended upgrade service does not run the garbage collector.  You will probably want to set up your own mcron job to run guix gc periodically.

     maximum-duration (default: 3600)
          Maximum duration in seconds for the upgrade; past that time, the upgrade aborts.

          This is primarily useful to ensure the upgrade does not end up rebuilding or re-downloading ``the world''.

     log-file (default: "/var/log/unattended-upgrade.log")
          File where unattended upgrades are logged.

X Window
--------

Support for the X Window graphical display system---specifically Xorg---is provided by the (gnu services xorg) module.  Note that there is no xorg-service procedure.  Instead, the X server is started by the login manager, by default the GNOME Display Manager (GDM).

GDM of course allows users to log in into window managers and desktop environments other than GNOME; for those using GNOME, GDM is required for features such as automatic screen locking.

To use X11, you must install at least one window manager---for example the windowmaker or openbox packages---preferably by adding it to the packages field of your operating system definition (see system-wide packages).

GDM also supports Wayland: it can itself use Wayland instead of X11 for its user interface, and it can also start Wayland sessions.  The former is required for the latter, to enable, set wayland? to #t in gdm-configuration.

 -- Variable: gdm-service-type
     This is the type for the GNOME Desktop Manager (https://wiki.gnome.org/Projects/GDM/) (GDM), a program that manages graphical display servers and handles graphical user logins.  Its value must be a gdm-configuration (see below).

     GDM looks for session types described by the .desktop files in /run/current-system/profile/share/xsessions (for X11 sessions) and /run/current-system/profile/share/wayland-sessions (for Wayland sessions) and allows users to choose a session from the log-in screen. Packages such as gnome, xfce, i3 and sway provide .desktop files; adding them to the system-wide set of packages automatically makes them available at the log-in screen.

     In addition, ~/.xsession files are honored.  When available, ~/.xsession must be an executable that starts a window manager and/or other X clients.

 -- Data Type: gdm-configuration

     auto-login? (default: #f)
     default-user (default: #f)
          When auto-login? is false, GDM presents a log-in screen.

          When auto-login? is true, GDM logs in directly as default-user.

     auto-suspend? (default #t)
          When true, GDM will automatically suspend to RAM when nobody is physically connected.  When a machine is used via remote desktop or SSH, this should be set to false to avoid GDM interrupting remote sessions or rendering the machine unavailable.

     debug? (default: #f)
          When true, GDM writes debug messages to its log.

     gnome-shell-assets (default: ...)
          List of GNOME Shell assets needed by GDM: icon theme, fonts, etc.

     xorg-configuration (default: (xorg-configuration))
          Configuration of the Xorg graphical server.

     x-session (default: (xinitrc))
          Script to run before starting a X session.

     xdmcp? (default: #f)
          When true, enable the X Display Manager Control Protocol (XDMCP).  This should only be enabled in trusted environments, as the protocol is not secure.  When enabled, GDM listens for XDMCP queries on the UDP port 177.

     dbus-daemon (default: dbus-daemon-wrapper)
          File name of the dbus-daemon executable.

     gdm (default: gdm)
          The GDM package to use.

     wayland? (default: #f)
          When true, enables Wayland in GDM, necessary to use Wayland sessions.

     wayland-session (default: gdm-wayland-session-wrapper)
          The Wayland session wrapper to use, needed to setup the environment.

 -- Variable: slim-service-type
     This is the type for the SLiM graphical login manager for X11.

     Like GDM, SLiM looks for session types described by .desktop files and allows users to choose a session from the log-in screen using F1.  It also honors ~/.xsession files.

     Unlike GDM, SLiM does not spawn the user session on a different VT after logging in, which means that you can only start one graphical session.  If you want to be able to run multiple graphical sessions at the same time you have to add multiple SLiM services to your system services.  The following example shows how to replace the default GDM service with two SLiM services on tty7 and tty8.

          (use-modules (gnu services)
                       (gnu services desktop)
                       (gnu services xorg))

          (operating-system
            ;; ...
            (services (cons* (service slim-service-type (slim-configuration
                                                         (display ":0")
                                                         (vt "vt7")))
                             (service slim-service-type (slim-configuration
                                                         (display ":1")
                                                         (vt "vt8")))
                             (modify-services %desktop-services
                               (delete gdm-service-type)))))

 -- Data Type: slim-configuration
     Data type representing the configuration of slim-service-type.

     allow-empty-passwords? (default: #t)
          Whether to allow logins with empty passwords.

     gnupg? (default: #f)
          If enabled, pam-gnupg will attempt to automatically unlock the user's GPG keys with the login password via gpg-agent.  The keygrips of all keys to be unlocked should be written to ~/.pam-gnupg, and can be queried with gpg -K --with-keygrip.  Presetting passphrases must be enabled by adding allow-preset-passphrase in ~/.gnupg/gpg-agent.conf.

     auto-login? (default: #f)
     default-user (default: "")
          When auto-login? is false, SLiM presents a log-in screen.

          When auto-login? is true, SLiM logs in directly as default-user.

     theme (default: %default-slim-theme)
     theme-name (default: %default-slim-theme-name)
          The graphical theme to use and its name.

     auto-login-session (default: #f)
          If true, this must be the name of the executable to start as the default session---e.g., (file-append windowmaker "/bin/windowmaker").

          If false, a session described by one of the available .desktop files in /run/current-system/profile and ~/.guix-profile will be used.

               You must install at least one window manager in the system profile or in your user profile.  Failing to do that, if auto-login-session is false, you will be unable to log in.

     xorg-configuration (default (xorg-configuration))
          Configuration of the Xorg graphical server.

     display (default ":0")
          The display on which to start the Xorg graphical server.

     vt (default "vt7")
          The VT on which to start the Xorg graphical server.

     xauth (default: xauth)
          The XAuth package to use.

     shepherd (default: shepherd)
          The Shepherd package used when invoking halt and reboot.

     sessreg (default: sessreg)
          The sessreg package used in order to register the session.

     slim (default: slim)
          The SLiM package to use.

 -- Variable: %default-theme
 -- Variable: %default-theme-name
     The default SLiM theme and its name.

 -- Variable: sddm-service-type
     This is the type of the service to run the SDDM display manager (https://github.com/sddm/sddm).  Its value must be a sddm-configuration record (see below).

     Here's an example use:

          (service sddm-service-type
                   (sddm-configuration
                     (auto-login-user "alice")
                     (auto-login-session "xfce.desktop")))

 -- Data Type: sddm-configuration
     This data type represents the configuration of the SDDM login manager. The available fields are:

     sddm (default: sddm)
          The SDDM package to use.

     display-server (default: "x11")
          Select display server to use for the greeter.  Valid values are "x11" or "wayland".

     numlock (default: "on")
          Valid values are "on", "off" or "none".

     halt-command (default #~(string-append #$shepherd "/sbin/halt"))
          Command to run when halting.

     reboot-command (default #~(string-append #$shepherd "/sbin/reboot"))
          Command to run when rebooting.

     theme (default "maldives")
          Theme to use.  Default themes provided by SDDM are "elarun", "maldives" or "maya".

     themes-directory (default "/run/current-system/profile/share/sddm/themes")
          Directory to look for themes.

     faces-directory (default "/run/current-system/profile/share/sddm/faces")
          Directory to look for faces.

     default-path (default "/run/current-system/profile/bin")
          Default PATH to use.

     minimum-uid (default: 1000)
          Minimum UID displayed in SDDM and allowed for log-in.

     maximum-uid (default: 2000)
          Maximum UID to display in SDDM.

     remember-last-user? (default #t)
          Remember last user.

     remember-last-session? (default #t)
          Remember last session.

     hide-users (default "")
          Usernames to hide from SDDM greeter.

     hide-shells (default #~(string-append #$shadow "/sbin/nologin"))
          Users with shells listed will be hidden from the SDDM greeter.

     session-command (default #~(string-append #$sddm "/share/sddm/scripts/wayland-session"))
          Script to run before starting a wayland session.

     sessions-directory (default "/run/current-system/profile/share/wayland-sessions")
          Directory to look for desktop files starting wayland sessions.

     xorg-configuration (default (xorg-configuration))
          Configuration of the Xorg graphical server.

     xauth-path (default #~(string-append #$xauth "/bin/xauth"))
          Path to xauth.

     xephyr-path (default #~(string-append #$xorg-server "/bin/Xephyr"))
          Path to Xephyr.

     xdisplay-start (default #~(string-append #$sddm "/share/sddm/scripts/Xsetup"))
          Script to run after starting xorg-server.

     xdisplay-stop (default #~(string-append #$sddm "/share/sddm/scripts/Xstop"))
          Script to run before stopping xorg-server.

     xsession-command (default: xinitrc)
          Script to run before starting a X session.

     xsessions-directory (default: "/run/current-system/profile/share/xsessions")
          Directory to look for desktop files starting X sessions.

     minimum-vt (default: 7)
          Minimum VT to use.

     auto-login-user (default "")
          User account that will be automatically logged in. Setting this to the empty string disables auto-login.

     auto-login-session (default "")
          The .desktop file name to use as the auto-login session, or the empty string.

     relogin? (default #f)
          Relogin after logout.

 -- Variable: lightdm-service-type
     This is the type of the service to run the LightDM display manager (https://github.com/canonical/lightdm).  Its value must be a lightdm-configuration record, which is documented below.  Among its distinguishing features are TigerVNC integration for easily remoting your desktop as well as support for the XDMCP protocol, which can be used by remote clients to start a session from the login manager.

     In its most basic form, it can be used simply as:

          (service lightdm-service-type)

     A more elaborate example making use of the VNC capabilities and enabling more features and verbose logs could look like:

          (service lightdm-service-type
                   (lightdm-configuration
                    (allow-empty-passwords? #t)
                    (xdmcp? #t)
                    (vnc-server? #t)
                    (vnc-server-command
                     (file-append tigervnc-server "/bin/Xvnc"
                                  "  -SecurityTypes None"))
                    (seats
                     (list (lightdm-seat-configuration
                            (name "*")
                            (user-session "ratpoison"))))))

 -- Data Type: lightdm-configuration
     Available lightdm-configuration fields are:

     lightdm (default: lightdm) (type: file-like)
          The lightdm package to use.

     allow-empty-passwords? (default: #f) (type: boolean)
          Whether users not having a password set can login.

     debug? (default: #f) (type: boolean)
          Enable verbose output.

     xorg-configuration (type: xorg-configuration)
          The default Xorg server configuration to use to generate the Xorg server start script.  It can be refined per seat via the xserver-command of the <lightdm-seat-configuration> record, if desired.

     greeters (type: list-of-greeter-configurations)
          The LightDM greeter configurations specifying the greeters to use.

     seats (type: list-of-seat-configurations)
          The seat configurations to use.  A LightDM seat is akin to a user.

     xdmcp? (default: #f) (type: boolean)
          Whether a XDMCP server should listen on port UDP 177.

     xdmcp-listen-address (type: maybe-string)
          The host or IP address the XDMCP server listens for incoming connections.  When unspecified, listen on for any hosts/IP addresses.

     vnc-server? (default: #f) (type: boolean)
          Whether a VNC server is started.

     vnc-server-command (type: file-like)
          The Xvnc command to use for the VNC server, it's possible to provide extra options not otherwise exposed along the command, for example to disable security:

               (vnc-server-command (file-append tigervnc-server "/bin/Xvnc"
                                                " -SecurityTypes None" ))

          Or to set a PasswordFile for the classic (unsecure) VncAuth mechanism:

               (vnc-server-command (file-append tigervnc-server "/bin/Xvnc"
                                                " -PasswordFile /var/lib/lightdm/.vnc/passwd"))

          The password file should be manually created using the vncpasswd command.  Note that LightDM will create new sessions for VNC users, which means they need to authenticate in the same way as local users would.

     vnc-server-listen-address (type: maybe-string)
          The host or IP address the VNC server listens for incoming connections. When unspecified, listen for any hosts/IP addresses.

     vnc-server-port (default: 5900) (type: number)
          The TCP port the VNC server should listen to.

     extra-config (default: '()) (type: list-of-strings)
          Extra configuration values to append to the LightDM configuration file.

 -- Data Type: lightdm-gtk-greeter-configuration
     Available lightdm-gtk-greeter-configuration fields are:

     lightdm-gtk-greeter (default: lightdm-gtk-greeter) (type: file-like)
          The lightdm-gtk-greeter package to use.

     assets (default: (adwaita-icon-theme gnome-themes-extra hicolor-icon-theme)) (type: list-of-file-likes)
          The list of packages complementing the greeter, such as package providing icon themes.

     theme-name (default: "Adwaita") (type: string)
          The name of the theme to use.

     icon-theme-name (default: "Adwaita") (type: string)
          The name of the icon theme to use.

     cursor-theme-name (default: "Adwaita") (type: string)
          The name of the cursor theme to use.

     cursor-theme-size (default: 16) (type: number)
          The size to use for the cursor theme.

     allow-debugging? (type: maybe-boolean)
          Set to #t to enable debug log level.

     background (type: file-like)
          The background image to use.

     at-spi-enabled? (default: #f) (type: boolean)
          Enable accessibility support through the Assistive Technology Service Provider Interface (AT-SPI).

     a11y-states (default: (contrast font keyboard reader)) (type: list-of-a11y-states)
          The accessibility features to enable, given as list of symbols.

     reader (type: maybe-file-like)
          The command to use to launch a screen reader.

     extra-config (default: '()) (type: list-of-strings)
          Extra configuration values to append to the LightDM GTK Greeter configuration file.

 -- Data Type: lightdm-seat-configuration
     Available lightdm-seat-configuration fields are:

     name (type: seat-name)
          The name of the seat.  An asterisk (*) can be used in the name to apply the seat configuration to all the seat names it matches.

     user-session (type: maybe-string)
          The session to use by default.  The session name must be provided as a lowercase string, such as "gnome", "ratpoison", etc.

     type (default: local) (type: seat-type)
          The type of the seat, either the local or xremote symbol.

     autologin-user (type: maybe-string)
          The username to automatically log in with by default.

     greeter-session (default: lightdm-gtk-greeter) (type: greeter-session)
          The greeter session to use, specified as a symbol.  Currently, only lightdm-gtk-greeter is supported.

     xserver-command (type: maybe-file-like)
          The Xorg server command to run.

     session-wrapper (type: file-like)
          The xinitrc session wrapper to use.

     extra-config (default: '()) (type: list-of-strings)
          Extra configuration values to append to the seat configuration section.

 -- Data Type: xorg-configuration
     This data type represents the configuration of the Xorg graphical display server.  Note that there is no Xorg service; instead, the X server is started by a ``display manager'' such as GDM, SDDM, LightDM or SLiM.  Thus, the configuration of these display managers aggregates an xorg-configuration record.

     modules (default: %default-xorg-modules)
          This is a list of module packages loaded by the Xorg server---e.g., xf86-video-vesa, xf86-input-keyboard, and so on.

     fonts (default: %default-xorg-fonts)
          This is a list of font directories to add to the server's font path.

     drivers (default: '())
          This must be either the empty list, in which case Xorg chooses a graphics driver automatically, or a list of driver names that will be tried in this order---e.g., '("modesetting" "vesa").

     resolutions (default: '())
          When resolutions is the empty list, Xorg chooses an appropriate screen resolution.  Otherwise, it must be a list of resolutions---e.g., '((1024 768) (640 480)).

     keyboard-layout (default: #f)
          If this is #f, Xorg uses the default keyboard layout---usually US English (``qwerty'') for a 105-key PC keyboard.

          Otherwise this must be a keyboard-layout object specifying the keyboard layout in use when Xorg is running.  See Keyboard Layout, for more information on how to specify the keyboard layout.

     extra-config (default: '())
          This is a list of strings or objects appended to the configuration file.  It is used to pass extra text to be added verbatim to the configuration file.

     server (default: xorg-server)
          This is the package providing the Xorg server.

     server-arguments (default: %default-xorg-server-arguments)
          This is the list of command-line arguments to pass to the X server.  The default is -nolisten tcp.

 -- Procedure: set-xorg-configuration config [login-manager-service-type]
     Tell the log-in manager (of type LOGIN-MANAGER-SERVICE-TYPE) to use CONFIG, an <xorg-configuration> record.

     Since the Xorg configuration is embedded in the log-in manager's configuration---e.g., gdm-configuration---this procedure provides a shorthand to set the Xorg configuration.

 -- Procedure: xorg-start-command [config]
     Return a startx script in which the modules, fonts, etc. specified in CONFIG, are available.  The result should be used in place of startx.

     Usually the X server is started by a login manager.

 -- Variable: screen-locker-service-type
     Type for a service that adds a package for a screen locker or screen saver to the set of setuid programs and/or add a PAM entry for it.  The value for this service is a <screen-locker-configuration> object.

     While the default behavior is to setup both a setuid program and PAM entry, these two methods are redundant.  Screen locker programs may not execute when PAM is configured and setuid is set on their executable.  In this case, using-setuid? can be set to #f.

     For example, to make XlockMore usable:

          (service screen-locker-service-type
                   (screen-locker-configuration
                     (name "xlock")
                     (program (file-append xlockmore "/bin/xlock"))))

     makes the good ol' XlockMore usable.

     For example, swaylock fails to execute when compiled with PAM support and setuid enabled.  One can thus disable setuid:

          (service screen-locker-service-type
                   (screen-locker-configuration
                     (name "swaylock")
                     (program (file-append swaylock "/bin/swaylock"))
                     (using-pam? #t)
                     (using-setuid? #f)))

 -- Data Type: screen-locker-configuration
     Available screen-locker-configuration fields are:

     name (type: string)
          Name of the screen locker.

     program (type: file-like)
          Path to the executable for the screen locker as a G-Expression.

     allow-empty-password? (default: #f) (type: boolean)
          Whether to allow empty passwords.

     using-pam? (default: #t) (type: boolean)
          Whether to setup PAM entry.

     using-setuid? (default: #t) (type: boolean)
          Whether to setup program as setuid binary.

Printing Services
-----------------

The (gnu services cups) module provides a Guix service definition for the CUPS printing service.  To add printer support to a Guix system, add a cups-service to the operating system definition:

 -- Variable: cups-service-type
     The service type for the CUPS print server.  Its value should be a valid CUPS configuration (see below).  To use the default settings, simply write:

          (service cups-service-type)

The CUPS configuration controls the basic things about your CUPS installation: what interfaces it listens on, what to do if a print job fails, how much logging to do, and so on.  To actually add a printer, you have to visit the http://localhost:631 URL, or use a tool such as GNOME's printer configuration services.  By default, configuring a CUPS service will generate a self-signed certificate if needed, for secure connections to the print server.

Suppose you want to enable the Web interface of CUPS and also add support for Epson printers via the epson-inkjet-printer-escpr package and for HP printers via the hplip-minimal package. You can do that directly, like this (you need to use the (gnu packages cups) module):

     (service cups-service-type
              (cups-configuration
                (web-interface? #t)
                (extensions
                  (list cups-filters epson-inkjet-printer-escpr hplip-minimal))))

     If you wish to use the Qt5 based GUI which comes with the hplip package then it is suggested that you install the hplip package, either in your OS configuration file or as your user.

The available configuration parameters follow.  Each parameter definition is preceded by its type; for example, string-list foo indicates that the foo parameter should be specified as a list of strings.  There is also a way to specify the configuration as a string, if you have an old cupsd.conf file that you want to port over from some other system; see the end for more details.

Available cups-configuration fields are:

 -- cups-configuration parameter: package cups
     The CUPS package.

 -- cups-configuration parameter: package-list extensions (default: (list brlaser cups-filters epson-inkjet-printer-escpr foomatic-filters hplip-minimal splix))
     Drivers and other extensions to the CUPS package.

 -- cups-configuration parameter: files-configuration files-configuration
     Configuration of where to write logs, what directories to use for print spools, and related privileged configuration parameters.

     Available files-configuration fields are:

      -- files-configuration parameter: log-location access-log
          Defines the access log filename.  Specifying a blank filename disables access log generation.  The value stderr causes log entries to be sent to the standard error file when the scheduler is running in the foreground, or to the system log daemon when run in the background.  The value syslog causes log entries to be sent to the system log daemon.  The server name may be included in filenames using the string %s, as in /var/log/cups/%s-access_log.

          Defaults to "/var/log/cups/access_log".

      -- files-configuration parameter: file-name cache-dir
          Where CUPS should cache data.

          Defaults to "/var/cache/cups".

      -- files-configuration parameter: string config-file-perm
          Specifies the permissions for all configuration files that the scheduler writes.

          Note that the permissions for the printers.conf file are currently masked to only allow access from the scheduler user (typically root). This is done because printer device URIs sometimes contain sensitive authentication information that should not be generally known on the system.  There is no way to disable this security feature.

          Defaults to "0640".

      -- files-configuration parameter: log-location error-log
          Defines the error log filename.  Specifying a blank filename disables error log generation.  The value stderr causes log entries to be sent to the standard error file when the scheduler is running in the foreground, or to the system log daemon when run in the background.  The value syslog causes log entries to be sent to the system log daemon.  The server name may be included in filenames using the string %s, as in /var/log/cups/%s-error_log.

          Defaults to "/var/log/cups/error_log".

      -- files-configuration parameter: string fatal-errors
          Specifies which errors are fatal, causing the scheduler to exit.  The kind strings are:

          none
               No errors are fatal.

          all
               All of the errors below are fatal.

          browse
               Browsing initialization errors are fatal, for example failed connections to the DNS-SD daemon.

          config
               Configuration file syntax errors are fatal.

          listen
               Listen or Port errors are fatal, except for IPv6 failures on the loopback or any addresses.

          log
               Log file creation or write errors are fatal.

          permissions
               Bad startup file permissions are fatal, for example shared TLS certificate and key files with world-read permissions.

          Defaults to "all -browse".

      -- files-configuration parameter: boolean file-device?
          Specifies whether the file pseudo-device can be used for new printer queues.  The URI file:///dev/null is always allowed.

          Defaults to #f.

      -- files-configuration parameter: string group
          Specifies the group name or ID that will be used when executing external programs.

          Defaults to "lp".

      -- files-configuration parameter: string log-file-group
          Specifies the group name or ID that will be used for log files.

          Defaults to "lpadmin".

      -- files-configuration parameter: string log-file-perm
          Specifies the permissions for all log files that the scheduler writes.

          Defaults to "0644".

      -- files-configuration parameter: log-location page-log
          Defines the page log filename.  Specifying a blank filename disables page log generation.  The value stderr causes log entries to be sent to the standard error file when the scheduler is running in the foreground, or to the system log daemon when run in the background.  The value syslog causes log entries to be sent to the system log daemon.  The server name may be included in filenames using the string %s, as in /var/log/cups/%s-page_log.

          Defaults to "/var/log/cups/page_log".

      -- files-configuration parameter: string remote-root
          Specifies the username that is associated with unauthenticated accesses by clients claiming to be the root user.  The default is remroot.

          Defaults to "remroot".

      -- files-configuration parameter: file-name request-root
          Specifies the directory that contains print jobs and other HTTP request data.

          Defaults to "/var/spool/cups".

      -- files-configuration parameter: sandboxing sandboxing
          Specifies the level of security sandboxing that is applied to print filters, backends, and other child processes of the scheduler; either relaxed or strict.  This directive is currently only used/supported on macOS.

          Defaults to strict.

      -- files-configuration parameter: file-name server-keychain
          Specifies the location of TLS certificates and private keys.  CUPS will look for public and private keys in this directory: .crt files for PEM-encoded certificates and corresponding .key files for PEM-encoded private keys.

          Defaults to "/etc/cups/ssl".

      -- files-configuration parameter: file-name server-root
          Specifies the directory containing the server configuration files.

          Defaults to "/etc/cups".

      -- files-configuration parameter: boolean sync-on-close?
          Specifies whether the scheduler calls fsync(2) after writing configuration or state files.

          Defaults to #f.

      -- files-configuration parameter: space-separated-string-list system-group
          Specifies the group(s) to use for @SYSTEM group authentication.

      -- files-configuration parameter: file-name temp-dir
          Specifies the directory where temporary files are stored.

          Defaults to "/var/spool/cups/tmp".

      -- files-configuration parameter: string user
          Specifies the user name or ID that is used when running external programs.

          Defaults to "lp".

      -- files-configuration parameter: string set-env
          Set the specified environment variable to be passed to child processes.

          Defaults to "variable value".

 -- cups-configuration parameter: access-log-level access-log-level
     Specifies the logging level for the AccessLog file.  The config level logs when printers and classes are added, deleted, or modified and when configuration files are accessed or updated.  The actions level logs when print jobs are submitted, held, released, modified, or canceled, and any of the conditions for config.  The all level logs all requests.

     Defaults to actions.

 -- cups-configuration parameter: boolean auto-purge-jobs?
     Specifies whether to purge job history data automatically when it is no longer required for quotas.

     Defaults to #f.

 -- cups-configuration parameter: comma-separated-string-list browse-dns-sd-sub-types
     Specifies a list of DNS-SD sub-types to advertise for each shared printer.

     The default (list "_cups" "_print" "_universal") tells clients that CUPS sharing, IPP Everywhere, AirPrint, and Mopria are supported.

 -- cups-configuration parameter: browse-local-protocols browse-local-protocols
     Specifies which protocols to use for local printer sharing.

     Defaults to dnssd.

 -- cups-configuration parameter: boolean browse-web-if?
     Specifies whether the CUPS web interface is advertised.

     Defaults to #f.

 -- cups-configuration parameter: boolean browsing?
     Specifies whether shared printers are advertised.

     Defaults to #f.

 -- cups-configuration parameter: default-auth-type default-auth-type
     Specifies the default type of authentication to use.

     Defaults to Basic.

 -- cups-configuration parameter: default-encryption default-encryption
     Specifies whether encryption will be used for authenticated requests.

     Defaults to Required.

 -- cups-configuration parameter: string default-language
     Specifies the default language to use for text and web content.

     Defaults to "en".

 -- cups-configuration parameter: string default-paper-size
     Specifies the default paper size for new print queues.  "Auto" uses a locale-specific default, while "None" specifies there is no default paper size.  Specific size names are typically "Letter" or "A4".

     Defaults to "Auto".

 -- cups-configuration parameter: string default-policy
     Specifies the default access policy to use.

     Defaults to "default".

 -- cups-configuration parameter: boolean default-shared?
     Specifies whether local printers are shared by default.

     Defaults to #t.

 -- cups-configuration parameter: non-negative-integer dirty-clean-interval
     Specifies the delay for updating of configuration and state files, in seconds.  A value of 0 causes the update to happen as soon as possible, typically within a few milliseconds.

     Defaults to 30.

 -- cups-configuration parameter: error-policy error-policy
     Specifies what to do when an error occurs.  Possible values are abort-job, which will discard the failed print job; retry-job, which will retry the job at a later time; retry-current-job, which retries the failed job immediately; and stop-printer, which stops the printer.

     Defaults to stop-printer.

 -- cups-configuration parameter: non-negative-integer filter-limit
     Specifies the maximum cost of filters that are run concurrently, which can be used to minimize disk, memory, and CPU resource problems.  A limit of 0 disables filter limiting.  An average print to a non-PostScript printer needs a filter limit of about 200.  A PostScript printer needs about half that (100).  Setting the limit below these thresholds will effectively limit the scheduler to printing a single job at any time.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer filter-nice
     Specifies the scheduling priority of filters that are run to print a job.  The nice value ranges from 0, the highest priority, to 19, the lowest priority.

     Defaults to 0.

 -- cups-configuration parameter: host-name-lookups host-name-lookups
     Specifies whether to do reverse lookups on connecting clients.  The double setting causes cupsd to verify that the hostname resolved from the address matches one of the addresses returned for that hostname.  Double lookups also prevent clients with unregistered addresses from connecting to your server.  Only set this option to #t or double if absolutely required.

     Defaults to #f.

 -- cups-configuration parameter: non-negative-integer job-kill-delay
     Specifies the number of seconds to wait before killing the filters and backend associated with a canceled or held job.

     Defaults to 30.

 -- cups-configuration parameter: non-negative-integer job-retry-interval
     Specifies the interval between retries of jobs in seconds.  This is typically used for fax queues but can also be used with normal print queues whose error policy is retry-job or retry-current-job.

     Defaults to 30.

 -- cups-configuration parameter: non-negative-integer job-retry-limit
     Specifies the number of retries that are done for jobs.  This is typically used for fax queues but can also be used with normal print queues whose error policy is retry-job or retry-current-job.

     Defaults to 5.

 -- cups-configuration parameter: boolean keep-alive?
     Specifies whether to support HTTP keep-alive connections.

     Defaults to #t.

 -- cups-configuration parameter: non-negative-integer limit-request-body
     Specifies the maximum size of print files, IPP requests, and HTML form data.  A limit of 0 disables the limit check.

     Defaults to 0.

 -- cups-configuration parameter: multiline-string-list listen
     Listens on the specified interfaces for connections.  Valid values are of the form ADDRESS:PORT, where ADDRESS is either an IPv6 address enclosed in brackets, an IPv4 address, or * to indicate all addresses.  Values can also be file names of local UNIX domain sockets.  The Listen directive is similar to the Port directive but allows you to restrict access to specific interfaces or networks.

 -- cups-configuration parameter: location-access-control-list location-access-controls
     Specifies a set of additional access controls.

     Available location-access-controls fields are:

      -- location-access-controls parameter: file-name path
          Specifies the URI path to which the access control applies.

      -- location-access-controls parameter: access-control-list access-controls
          Access controls for all access to this path, in the same format as the access-controls of operation-access-control.

          Defaults to '().

      -- location-access-controls parameter: method-access-control-list method-access-controls
          Access controls for method-specific access to this path.

          Defaults to '().

          Available method-access-controls fields are:

           -- method-access-controls parameter: boolean reverse?
               If #t, apply access controls to all methods except the listed methods.  Otherwise apply to only the listed methods.

               Defaults to #f.

           -- method-access-controls parameter: method-list methods
               Methods to which this access control applies.

               Defaults to '().

           -- method-access-controls parameter: access-control-list access-controls
               Access control directives, as a list of strings.  Each string should be one directive, such as "Order allow,deny".

               Defaults to '().

 -- cups-configuration parameter: non-negative-integer log-debug-history
     Specifies the number of debugging messages that are retained for logging if an error occurs in a print job.  Debug messages are logged regardless of the LogLevel setting.

     Defaults to 100.

 -- cups-configuration parameter: log-level log-level
     Specifies the level of logging for the ErrorLog file.  The value none stops all logging while debug2 logs everything.

     Defaults to info.

 -- cups-configuration parameter: log-time-format log-time-format
     Specifies the format of the date and time in the log files.  The value standard logs whole seconds while usecs logs microseconds.

     Defaults to standard.

 -- cups-configuration parameter: non-negative-integer max-clients
     Specifies the maximum number of simultaneous clients that are allowed by the scheduler.

     Defaults to 100.

 -- cups-configuration parameter: non-negative-integer max-clients-per-host
     Specifies the maximum number of simultaneous clients that are allowed from a single address.

     Defaults to 100.

 -- cups-configuration parameter: non-negative-integer max-copies
     Specifies the maximum number of copies that a user can print of each job.

     Defaults to 9999.

 -- cups-configuration parameter: non-negative-integer max-hold-time
     Specifies the maximum time a job may remain in the indefinite hold state before it is canceled.  A value of 0 disables cancellation of held jobs.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-jobs
     Specifies the maximum number of simultaneous jobs that are allowed.  Set to 0 to allow an unlimited number of jobs.

     Defaults to 500.

 -- cups-configuration parameter: non-negative-integer max-jobs-per-printer
     Specifies the maximum number of simultaneous jobs that are allowed per printer.  A value of 0 allows up to max-jobs per printer.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-jobs-per-user
     Specifies the maximum number of simultaneous jobs that are allowed per user.  A value of 0 allows up to max-jobs per user.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-job-time
     Specifies the maximum time a job may take to print before it is canceled, in seconds.  Set to 0 to disable cancellation of ``stuck'' jobs.

     Defaults to 10800.

 -- cups-configuration parameter: non-negative-integer max-log-size
     Specifies the maximum size of the log files before they are rotated, in bytes.  The value 0 disables log rotation.

     Defaults to 1048576.

 -- cups-configuration parameter: non-negative-integer max-subscriptions
     Specifies the maximum number of simultaneous event subscriptions that are allowed.  Set to 0 to allow an unlimited number of subscriptions.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-subscriptions-per-job
     Specifies the maximum number of simultaneous event subscriptions that are allowed per job.  A value of 0 allows up to max-subscriptions per job.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-subscriptions-per-printer
     Specifies the maximum number of simultaneous event subscriptions that are allowed per printer.  A value of 0 allows up to max-subscriptions per printer.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer max-subscriptions-per-user
     Specifies the maximum number of simultaneous event subscriptions that are allowed per user.  A value of 0 allows up to max-subscriptions per user.

     Defaults to 0.

 -- cups-configuration parameter: non-negative-integer multiple-operation-timeout
     Specifies the maximum amount of time to allow between files in a multiple file print job, in seconds.

     Defaults to 900.

 -- cups-configuration parameter: environment-variables environment-variables
     Passes the specified environment variable(s) to child processes; a list of strings.

     Defaults to '().

 -- cups-configuration parameter: policy-configuration-list policies
     Specifies named access control policies.

     Available policy-configuration fields are:

      -- policy-configuration parameter: string name
          Name of the policy.

      -- policy-configuration parameter: string job-private-access
          Specifies an access list for a job's private values.  @ACL maps to the printer's requesting-user-name-allowed or requesting-user-name-denied values.  @OWNER maps to the job's owner.  @SYSTEM maps to the groups listed for the system-group field of the files-configuration, which is reified into the cups-files.conf(5) file.  Other possible elements of the access list include specific user names, and @GROUP to indicate members of a specific group.  The access list may also be simply all or default.

          Defaults to "@OWNER @SYSTEM".

      -- policy-configuration parameter: string job-private-values
          Specifies the list of job values to make private, or all, default, or none.

          Defaults to "job-name job-originating-host-name job-originating-user-name phone".

      -- policy-configuration parameter: string subscription-private-access
          Specifies an access list for a subscription's private values. @ACL maps to the printer's requesting-user-name-allowed or requesting-user-name-denied values.  @OWNER maps to the job's owner.  @SYSTEM maps to the groups listed for the system-group field of the files-configuration, which is reified into the cups-files.conf(5) file.  Other possible elements of the access list include specific user names, and @GROUP to indicate members of a specific group.  The access list may also be simply all or default.

          Defaults to "@OWNER @SYSTEM".

      -- policy-configuration parameter: string subscription-private-values
          Specifies the list of job values to make private, or all, default, or none.

          Defaults to "notify-events notify-pull-method notify-recipient-uri notify-subscriber-user-name notify-user-data".

      -- policy-configuration parameter: operation-access-control-list access-controls
          Access control by IPP operation.

          Defaults to '().

 -- cups-configuration parameter: boolean-or-non-negative-integer preserve-job-files
     Specifies whether job files (documents) are preserved after a job is printed.  If a numeric value is specified, job files are preserved for the indicated number of seconds after printing.  Otherwise a boolean value applies indefinitely.

     Defaults to 86400.

 -- cups-configuration parameter: boolean-or-non-negative-integer preserve-job-history
     Specifies whether the job history is preserved after a job is printed. If a numeric value is specified, the job history is preserved for the indicated number of seconds after printing.  If #t, the job history is preserved until the MaxJobs limit is reached.

     Defaults to #t.

 -- cups-configuration parameter: comma-separated-string-list-or-#f ready-paper-sizes
     Specifies a list of potential paper sizes that are reported as ready, that is: loaded.  The actual list will contain only the sizes that each printer supports.

     The default value of #f is a special case: CUPS will use (list \"Letter\" \"Legal\" \"Tabloid\" \"4x6\" \"Env10\") if the default paper size is \"Letter\", and (list \"A3\" \"A4\" \"A5\" \"A6\" \"EnvDL\") otherwise.

 -- cups-configuration parameter: non-negative-integer reload-timeout
     Specifies the amount of time to wait for job completion before restarting the scheduler.

     Defaults to 30.

 -- cups-configuration parameter: string server-admin
     Specifies the email address of the server administrator.

     Defaults to "root@localhost.localdomain".

 -- cups-configuration parameter: host-name-list-or-* server-alias
     The ServerAlias directive is used for HTTP Host header validation when clients connect to the scheduler from external interfaces.  Using the special name * can expose your system to known browser-based DNS rebinding attacks, even when accessing sites through a firewall.  If the auto-discovery of alternate names does not work, we recommend listing each alternate name with a ServerAlias directive instead of using *.

     Defaults to *.

 -- cups-configuration parameter: string server-name
     Specifies the fully-qualified host name of the server.

     Defaults to "localhost".

 -- cups-configuration parameter: server-tokens server-tokens
     Specifies what information is included in the Server header of HTTP responses.  None disables the Server header.  ProductOnly reports CUPS.  Major reports CUPS 2.  Minor reports CUPS 2.0.  Minimal reports CUPS 2.0.0. OS reports CUPS 2.0.0 (UNAME) where UNAME is the output of the uname command.  Full reports CUPS 2.0.0 (UNAME) IPP/2.0.

     Defaults to Minimal.

 -- cups-configuration parameter: multiline-string-list ssl-listen
     Listens on the specified interfaces for encrypted connections.  Valid values are of the form ADDRESS:PORT, where ADDRESS is either an IPv6 address enclosed in brackets, an IPv4 address, or * to indicate all addresses.

     Defaults to '().

 -- cups-configuration parameter: ssl-options ssl-options
     Sets encryption options.  By default, CUPS only supports encryption using TLS v1.0 or higher using known secure cipher suites.  Security is reduced when Allow options are used, and enhanced when Deny options are used.  The AllowRC4 option enables the 128-bit RC4 cipher suites, which are required for some older clients.  The AllowSSL3 option enables SSL v3.0, which is required for some older clients that do not support TLS v1.0.  The DenyCBC option disables all CBC cipher suites.  The DenyTLS1.0 option disables TLS v1.0 support - this sets the minimum protocol version to TLS v1.1.

     Defaults to '().

 -- cups-configuration parameter: boolean strict-conformance?
     Specifies whether the scheduler requires clients to strictly adhere to the IPP specifications.

     Defaults to #f.

 -- cups-configuration parameter: non-negative-integer timeout
     Specifies the HTTP request timeout, in seconds.

     Defaults to 900.

 -- cups-configuration parameter: boolean web-interface?
     Specifies whether the web interface is enabled.

     Defaults to #f.

At this point you're probably thinking ``oh dear, Guix manual, I like you but you can stop already with the configuration options''.  Indeed. However, one more point: it could be that you have an existing cupsd.conf that you want to use.  In that case, you can pass an opaque-cups-configuration as the configuration of a cups-service-type.

Available opaque-cups-configuration fields are:

 -- opaque-cups-configuration parameter: package cups
     The CUPS package.

 -- opaque-cups-configuration parameter: string cupsd.conf
     The contents of the cupsd.conf, as a string.

 -- opaque-cups-configuration parameter: string cups-files.conf
     The contents of the cups-files.conf file, as a string.

For example, if your cupsd.conf and cups-files.conf are in strings of the same name, you could instantiate a CUPS service like this:

     (service cups-service-type
              (opaque-cups-configuration
                (cupsd.conf cupsd.conf)
                (cups-files.conf cups-files.conf)))

Desktop Services
----------------

The (gnu services desktop) module provides services that are usually useful in the context of a ``desktop'' setup---that is, on a machine running a graphical display server, possibly with graphical user interfaces, etc.  It also defines services that provide specific desktop environments like GNOME, Xfce or MATE.

To simplify things, the module defines a variable containing the set of services that users typically expect on a machine with a graphical environment and networking:

 -- Variable: %desktop-services
     This is a list of services that builds upon %base-services and adds or adjusts services for a typical ``desktop'' setup.

     In particular, it adds a graphical login manager (see gdm-service-type), screen lockers, a network management tool (see network-manager-service-type) with modem support (see modem-manager-service-type), energy and color management services, the elogind login and seat manager, the Polkit privilege service, the GeoClue location service, the AccountsService daemon that allows authorized users change system passwords, a NTP client (see Networking Services) and the Avahi daemon.

The %desktop-services variable can be used as the services field of an operating-system declaration (see services).

Additionally, the gnome-desktop-service-type, xfce-desktop-service, mate-desktop-service-type, lxqt-desktop-service-type and enlightenment-desktop-service-type procedures can add GNOME, Xfce, MATE and/or Enlightenment to a system.  To ``add GNOME'' means that system-level services like the backlight adjustment helpers and the power management utilities are added to the system, extending polkit and dbus appropriately, allowing GNOME to operate with elevated privileges on a limited number of special-purpose system interfaces. Additionally, adding a service made by gnome-desktop-service-type adds the GNOME metapackage to the system profile.  Likewise, adding the Xfce service not only adds the xfce metapackage to the system profile, but it also gives the Thunar file manager the ability to open a ``root-mode'' file management window, if the user authenticates using the administrator's password via the standard polkit graphical interface.  To ``add MATE'' means that polkit and dbus are extended appropriately, allowing MATE to operate with elevated privileges on a limited number of special-purpose system interfaces.  Additionally, adding a service of type mate-desktop-service-type adds the MATE metapackage to the system profile.  ``Adding Enlightenment'' means that dbus is extended appropriately, and several of Enlightenment's binaries are set as setuid, allowing Enlightenment's screen locker and other functionality to work as expected.

The desktop environments in Guix use the Xorg display server by default.  If you'd like to use the newer display server protocol called Wayland, you need to enable Wayland support in GDM (see wayland-gdm).  Another solution is to use the sddm-service instead of GDM as the graphical login manager. You should then select the ``GNOME (Wayland)'' session in SDDM. Alternatively you can also try starting GNOME on Wayland manually from a TTY with the command ``XDG_SESSION_TYPE=wayland exec dbus-run-session gnome-session``.  Currently only GNOME has support for Wayland.

 -- Variable: gnome-desktop-service-type
     This is the type of the service that adds the GNOME (https://www.gnome.org) desktop environment.  Its value is a gnome-desktop-configuration object (see below).

     This service adds the gnome package to the system profile, and extends polkit with the actions from gnome-settings-daemon.

 -- Data Type: gnome-desktop-configuration
     Configuration record for the GNOME desktop environment.

     gnome (default: gnome)
          The GNOME package to use.

 -- Variable: plasma-desktop-service-type
     This is the type of the service that adds the Plasma (https://kde.org/plasma-desktop/) desktop environment.  Its value is a plasma-desktop-configuration object (see below).

     This service adds the plasma package to the system profile.

 -- Data Type: plasma-desktop-configuration
     Configuration record for the Plasma desktop environment.

     plasma (default: plasma)
          The Plasma package to use.

 -- Variable: xfce-desktop-service-type
     This is the type of a service to run the https://xfce.org/ (Xfce) desktop environment.  Its value is an xfce-desktop-configuration object (see below).

     This service adds the xfce package to the system profile, and extends polkit with the ability for thunar to manipulate the file system as root from within a user session, after the user has authenticated with the administrator's password.

     Note that xfce4-panel and its plugin packages should be installed in the same profile to ensure compatibility.  When using this service, you should add extra plugins (xfce4-whiskermenu-plugin, xfce4-weather-plugin, etc.) to the packages field of your operating-system.

 -- Data Type: xfce-desktop-configuration
     Configuration record for the Xfce desktop environment.

     xfce (default: xfce)
          The Xfce package to use.

 -- Variable: mate-desktop-service-type
     This is the type of the service that runs the MATE desktop environment (https://mate-desktop.org/).  Its value is a mate-desktop-configuration object (see below).

     This service adds the mate package to the system profile, and extends polkit with the actions from mate-settings-daemon.

 -- Data Type: mate-desktop-configuration
     Configuration record for the MATE desktop environment.

     mate (default: mate)
          The MATE package to use.

 -- Variable: lxqt-desktop-service-type
     This is the type of the service that runs the LXQt desktop environment (https://lxqt-project.org).  Its value is a lxqt-desktop-configuration object (see below).

     This service adds the lxqt package to the system profile.

 -- Data Type: lxqt-desktop-configuration
     Configuration record for the LXQt desktop environment.

     lxqt (default: lxqt)
          The LXQT package to use.

 -- Variable: sugar-desktop-service-type
     This is the type of the service that runs the Sugar desktop environment (https://www.sugarlabs.org).  Its value is a sugar-desktop-configuration object (see below).

     This service adds the sugar package to the system profile, as well as any selected Sugar activities.  By default it only includes a minimal set of activities.

 -- Data Type: sugar-desktop-configuration
     Configuration record for the Sugar desktop environment.

     sugar (default: sugar)
          The Sugar package to use.

     gobject-introspection (default: gobject-introspection)
          The gobject-introspection package to use.  This package is used to access libraries installed as dependencies of Sugar activities.

     activities (default: (list sugar-help-activity))
          A list of Sugar activities to install.

The following example configures the Sugar desktop environment with a number of useful activities:

     (use-modules (gnu))
     (use-package-modules sugar)
     (use-service-modules desktop)
     (operating-system
       ...
       (services (cons* (service sugar-desktop-service-type
                                 (sugar-desktop-configuration
                                   (activities (list sugar-browse-activity
                                                     sugar-help-activity
                                                     sugar-jukebox-activity
                                                     sugar-typing-turtle-activity))))
                        %desktop-services))
       ...)

 -- Variable: enlightenment-desktop-service-type
     Return a service that adds the enlightenment package to the system profile, and extends dbus with actions from efl.

 -- Data Type: enlightenment-desktop-service-configuration

     enlightenment (default: enlightenment)
          The enlightenment package to use.

Because the GNOME, Xfce and MATE desktop services pull in so many packages, the default %desktop-services variable doesn't include any of them by default.  To add GNOME, Xfce or MATE, just cons them onto %desktop-services in the services field of your operating-system:

     (use-modules (gnu))
     (use-service-modules desktop)
     (operating-system
       ...
       ;; cons* adds items to the list given as its last argument.
       (services (cons* (service gnome-desktop-service-type)
                        (service xfce-desktop-service)
                        %desktop-services))
       ...)

These desktop environments will then be available as options in the graphical login window.

The actual service definitions included in %desktop-services and provided by (gnu services dbus) and (gnu services desktop) are described below.

 -- Variable: dbus-root-service-type
     Type for a service that runs the D-Bus ``system bus''. (D-Bus (https://dbus.freedesktop.org/) is an inter-process communication facility.  Its system bus is used to allow system services to communicate and to be notified of system-wide events.)

     The value for this service type is a <dbus-configuration> record.

 -- Data Type: dbus-configuration
     Data type representing the configuration for dbus-root-service-type.

     dbus (default: dbus) (type: file-like)
          Package object for dbus.

     services (default: '()) (type: list)
          List of packages that provide an etc/dbus-1/system.d directory containing additional D-Bus configuration and policy files. For example, to allow avahi-daemon to use the system bus, SERVICES must be equal to (list avahi).

     verbose? (default: #f) (type: boolean)
          When #t, D-Bus is launched with environment variable DBUS_VERBOSE set to 1.  A verbose-enabled D-Bus package such as dbus-verbose should be provided to DBUS in this scenario. The verbose output is logged to /var/log/dbus-daemon.log.

Elogind
.......

Elogind (https://github.com/elogind/elogind) is a login and seat management daemon that also handles most system-level power events for a computer, for example suspending the system when a lid is closed, or shutting it down when the power button is pressed.

It also provides a D-Bus interface that can be used to know which users are logged in, know what kind of sessions they have open, suspend the system, inhibit system suspend, reboot the system, and other tasks.

 -- Variable: elogind-service-type
     Type of the service that runs elogind, a login and seat management daemon.  The value for this service is a <elogind-configuration> object.

 -- Data Type: elogind-configuration
     Data type representing the configuration of elogind.

     elogind (default: elogind) (type: file-like)
          ...

     kill-user-processes? (default: #f) (type: boolean)
          ...

     kill-only-users (default: '()) (type: list)
          ...

     kill-exclude-users (default: '("root")) (type: list-of-string)
          ...

     inhibit-delay-max-seconds (default: 5) (type: integer)
          ...

     handle-power-key (default: 'poweroff) (type: symbol)
          ...

     handle-suspend-key (default: 'suspend) (type: symbol)
          ...

     handle-hibernate-key (default: 'hibernate) (type: symbol)
          ...

     handle-lid-switch (default: 'suspend) (type: symbol)
          ...

     handle-lid-switch-docked (default: 'ignore) (type: symbol)
          ...

     handle-lid-switch-external-power (default: *unspecified*) (type: symbol)
          ...

     power-key-ignore-inhibited? (default: #f) (type: boolean)
          ...

     suspend-key-ignore-inhibited? (default: #f) (type: boolean)
          ...

     hibernate-key-ignore-inhibited? (default: #f) (type: boolean)
          ...

     lid-switch-ignore-inhibited? (default: #t) (type: boolean)
          ...

     holdoff-timeout-seconds (default: 30) (type: integer)
          ...

     idle-action (default: 'ignore) (type: symbol)
          ...

     idle-action-seconds (default: (* 30 60)) (type: integer)
          ...

     runtime-directory-size-percent (default: 10) (type: integer)
          ...

     runtime-directory-size (default: #f) (type: integer)
          ...

     remove-ipc? (default: #t) (type: boolean)
          ...

     suspend-state (default: '("mem" "standby" "freeze")) (type: list)
          ...

     suspend-mode (default: '()) (type: list)
          ...

     hibernate-state (default: '("disk")) (type: list)
          ...

     hibernate-mode (default: '("platform" "shutdown")) (type: list)
          ...

     hybrid-sleep-state (default: '("disk")) (type: list)
          ...

     hybrid-sleep-mode (default: '("suspend" "platform" "shutdown")) (type: list)
          ...

 -- Variable: accountsservice-service-type
     Type for the service that runs AccountsService, a system service that can list available accounts, change their passwords, and so on. AccountsService integrates with PolicyKit to enable unprivileged users to acquire the capability to modify their system configuration. See AccountsService (https://www.freedesktop.org/wiki/Software/AccountsService/) for more information.

     The value for this service is a file-like object, by default it is set to accountsservice (the package object for AccountsService).

 -- Variable: polkit-service-type
     Type for the service that runs the Polkit privilege management service (https://www.freedesktop.org/wiki/Software/polkit/), which allows system administrators to grant access to privileged operations in a structured way.  By querying the Polkit service, a privileged system component can know when it should grant additional capabilities to ordinary users.  For example, an ordinary user can be granted the capability to suspend the system if the user is logged in locally.

     The value for this service is a <polkit-configuration> object.

 -- Variable: polkit-wheel-service
     Service that adds the wheel group as admins to the Polkit service.  This makes it so that users in the wheel group are queried for their own passwords when performing administrative actions instead of root's, similar to the behaviour used by sudo.

 -- Variable: upower-service-type
     Service that runs upowerd (https://upower.freedesktop.org/), a system-wide monitor for power consumption and battery levels, with the given configuration settings.

     It implements the org.freedesktop.UPower D-Bus interface, and is notably used by GNOME.

 -- Data Type: upower-configuration
     Data type representation the configuration for UPower.

     upower (default: UPOWER)
          Package to use for upower.

     watts-up-pro? (default: #f)
          Enable the Watts Up Pro device.

     poll-batteries? (default: #t)
          Enable polling the kernel for battery level changes.

     ignore-lid? (default: #f)
          Ignore the lid state, this can be useful if it's incorrect on a device.

     use-percentage-for-policy? (default: #t)
          Whether to use a policy based on battery percentage rather than on estimated time left.  A policy based on battery percentage is usually more reliable.

     percentage-low (default: 20)
          When use-percentage-for-policy? is #t, this sets the percentage at which the battery is considered low.

     percentage-critical (default: 5)
          When use-percentage-for-policy? is #t, this sets the percentage at which the battery is considered critical.

     percentage-action (default: 2)
          When use-percentage-for-policy? is #t, this sets the percentage at which action will be taken.

     time-low (default: 1200)
          When use-time-for-policy? is #f, this sets the time remaining in seconds at which the battery is considered low.

     time-critical (default: 300)
          When use-time-for-policy? is #f, this sets the time remaining in seconds at which the battery is considered critical.

     time-action (default: 120)
          When use-time-for-policy? is #f, this sets the time remaining in seconds at which action will be taken.

     critical-power-action (default: 'hybrid-sleep)
          The action taken when percentage-action or time-action is reached (depending on the configuration of use-percentage-for-policy?).

          Possible values are:

            * 'power-off

            * 'hibernate

            * 'hybrid-sleep.

 -- Variable: udisks-service-type
     Type for the service that runs UDisks (https://udisks.freedesktop.org/docs/latest/), a disk management daemon that provides user interfaces with notifications and ways to mount/unmount disks.  Programs that talk to UDisks include the udisksctl command, part of UDisks, and GNOME Disks.  Note that Udisks relies on the mount command, so it will only be able to use the file-system utilities installed in the system profile.  For example if you want to be able to mount NTFS file-systems in read and write fashion, you'll need to have ntfs-3g installed system-wide.

     The value for this service is a <udisks-configuration> object.

 -- Data Type: udisks-configuration
     Data type representing the configuration for udisks-service-type.

     udisks (default: udisks) (type: file-like)
          Package object for UDisks.

 -- Variable: colord-service-type
     This is the type of the service that runs colord, a system service with a D-Bus interface to manage the color profiles of input and output devices such as screens and scanners.  It is notably used by the GNOME Color Manager graphical tool.  See the colord web site (https://www.freedesktop.org/software/colord/) for more information.

 -- Variable: sane-service-type
     This service provides access to scanners via SANE (http://www.sane-project.org) by installing the necessary udev rules.  It is included in %desktop-services (see Desktop Services) and relies by default on sane-backends-minimal package (see below) for hardware support.

 -- Variable: sane-backends-minimal
     The default package which the sane-service-type installs.  It supports many recent scanners.

 -- Variable: sane-backends
     This package includes support for all scanners that sane-backends-minimal supports, plus older Hewlett-Packard scanners supported by hplip package.  In order to use this on a system which relies on %desktop-services, you may use modify-services (see modify-services) as illustrated below:

          (use-modules (gnu))
          (use-service-modules
            ...
            desktop)
          (use-package-modules
            ...
            scanner)

          (define %my-desktop-services
            ;; List of desktop services that supports a broader range of scanners.
            (modify-services %desktop-services
              (sane-service-type _ => sane-backends)))

          (operating-system
            ...
            (services %my-desktop-services))

 -- Procedure: geoclue-application name [#:allowed? #t] [#:system? #f] [#:users '()]
     Return a configuration allowing an application to access GeoClue location data.  NAME is the Desktop ID of the application, without the .desktop part.  If ALLOWED? is true, the application will have access to location information by default.  The boolean SYSTEM?  value indicates whether an application is a system component or not.  Finally USERS is a list of UIDs of all users for which this application is allowed location info access.  An empty users list means that all users are allowed.

 -- Variable: %standard-geoclue-applications
     The standard list of well-known GeoClue application configurations, granting authority to the GNOME date-and-time utility to ask for the current location in order to set the time zone, and allowing the IceCat and Epiphany web browsers to request location information. IceCat and Epiphany both query the user before allowing a web page to know the user's location.

 -- Variable: geoclue-service-type
     Type for the service that runs the GeoClue (https://wiki.freedesktop.org/www/Software/GeoClue/) location service.  This service provides a D-Bus interface to allow applications to request access to a user's physical location, and optionally to add information to online location databases.

     The value for this service is a <geoclue-configuration> object.

 -- Variable: bluetooth-service-type
     This is the type for the Linux Bluetooth Protocol Stack (https://bluez.org/) (BlueZ) system, which generates the /etc/bluetooth/main.conf configuration file.  The value for this type is a bluetooth-configuration record as in this example:

          (service bluetooth-service-type)

     See below for details about bluetooth-configuration.

 -- Data Type: bluetooth-configuration
     Data type representing the configuration for bluetooth-service.

     bluez (default: bluez)
          bluez package to use.

     name (default: "BlueZ")
          Default adapter name.

     class (default: #x000000)
          Default device class. Only the major and minor device class bits are considered.

     discoverable-timeout (default: 180)
          How long to stay in discoverable mode before going back to non-discoverable. The value is in seconds.

     always-pairable? (default: #f)
          Always allow pairing even if there are no agents registered.

     pairable-timeout (default: 0)
          How long to stay in pairable mode before going back to non-discoverable. The value is in seconds.

     device-id (default: #f)
          Use vendor id source (assigner), vendor, product and version information for DID profile support. The values are separated by ":" and ASSIGNER, VID, PID and VERSION.

          Possible values are:

            * #f to disable it,

            * "assigner:1234:5678:abcd", where ASSIGNER is either usb (default) or bluetooth.

     reverse-service-discovery? (default: #t)
          Do reverse service discovery for previously unknown devices that connect to us. For BR/EDR this option is really only needed for qualification since the BITE tester doesn't like us doing reverse SDP for some test cases, for LE this disables the GATT client functionally so it can be used in system which can only operate as peripheral.

     name-resolving? (default: #t)
          Enable name resolving after inquiry. Set it to #f if you don't need remote devices name and want shorter discovery cycle.

     debug-keys? (default: #f)
          Enable runtime persistency of debug link keys. Default is false which makes debug link keys valid only for the duration of the connection that they were created for.

     controller-mode (default: 'dual)
          Restricts all controllers to the specified transport. 'dual means both BR/EDR and LE are enabled (if supported by the hardware).

          Possible values are:

            * 'dual

            * 'bredr

            * 'le

     multi-profile (default: 'off)
          Enables Multi Profile Specification support. This allows to specify if system supports only Multiple Profiles Single Device (MPSD) configuration or both Multiple Profiles Single Device (MPSD) and Multiple Profiles Multiple Devices (MPMD) configurations.

          Possible values are:

            * 'off

            * 'single

            * 'multiple

     fast-connectable? (default: #f)
          Permanently enables the Fast Connectable setting for adapters that support it. When enabled other devices can connect faster to us, however the tradeoff is increased power consumptions. This feature will fully work only on kernel version 4.1 and newer.

     privacy (default: 'off)
          Default privacy settings.

            * 'off: Disable local privacy

            * 'network/on: A device will only accept advertising packets from peer devices that contain private addresses. It may not be compatible with some legacy devices since it requires the use of RPA(s) all the time

            * 'device: A device in device privacy mode is only concerned about the privacy of the device and will accept advertising packets from peer devices that contain their Identity Address as well as ones that contain a private address, even if the peer device has distributed its IRK in the past

          and additionally, if CONTROLLER-MODE is set to 'dual:

            * 'limited-network: Apply Limited Discoverable Mode to advertising, which follows the same policy as to BR/EDR that publishes the identity address when discoverable, and Network Privacy Mode for scanning

            * 'limited-device: Apply Limited Discoverable Mode to advertising, which follows the same policy as to BR/EDR that publishes the identity address when discoverable, and Device Privacy Mode for scanning.

     just-works-repairing (default: 'never)
          Specify the policy to the JUST-WORKS repairing initiated by peer.

          Possible values:

            * 'never

            * 'confirm

            * 'always

     temporary-timeout (default: 30)
          How long to keep temporary devices around. The value is in seconds. 0 disables the timer completely.

     refresh-discovery? (default: #t)
          Enables the device to issue an SDP request to update known services when profile is connected.

     experimental (default: #f)
          Enables experimental features and interfaces, alternatively a list of UUIDs can be given.

          Possible values:

            * #t

            * #f

            * (list (uuid <uuid-1>) (uuid <uuid-2>) ...).

          List of possible UUIDs:

            * d4992530-b9ec-469f-ab01-6c481c47da1c: BlueZ Experimental Debug,

            * 671b10b5-42c0-4696-9227-eb28d1b049d6: BlueZ Experimental Simultaneous Central and Peripheral,

            * 15c0a148-c273-11ea-b3de-0242ac130004: BlueZ Experimental LL privacy,

            * 330859bc-7506-492d-9370-9a6f0614037f: BlueZ Experimental Bluetooth Quality Report,

            * a6695ace-ee7f-4fb9-881a-5fac66c629af: BlueZ Experimental Offload Codecs.

     remote-name-request-retry-delay (default: 300)
          The duration to avoid retrying to resolve a peer's name, if the previous try failed.

     page-scan-type (default: #f)
          BR/EDR Page scan activity type.

     page-scan-interval (default: #f)
          BR/EDR Page scan activity interval.

     page-scan-window (default: #f)
          BR/EDR Page scan activity window.

     inquiry-scan-type (default: #f)
          BR/EDR Inquiry scan activity type.

     inquiry-scan-interval (default: #f)
          BR/EDR Inquiry scan activity interval.

     inquiry-scan-window (default: #f)
          BR/EDR Inquiry scan activity window.

     link-supervision-timeout (default: #f)
          BR/EDR Link supervision timeout.

     page-timeout (default: #f)
          BR/EDR Page timeout.

     min-sniff-interval (default: #f)
          BR/EDR minimum sniff interval.

     max-sniff-interval (default: #f)
          BR/EDR maximum sniff interval.

     min-advertisement-interval (default: #f)
          LE minimum advertisement interval (used for legacy advertisement only).

     max-advertisement-interval (default: #f)
          LE maximum advertisement interval (used for legacy advertisement only).

     multi-advertisement-rotation-interval (default: #f)
          LE multiple advertisement rotation interval.

     scan-interval-auto-connect (default: #f)
          LE scanning interval used for passive scanning supporting auto connect.

     scan-window-auto-connect (default: #f)
          LE scanning window used for passive scanning supporting auto connect.

     scan-interval-suspend (default: #f)
          LE scanning interval used for active scanning supporting wake from suspend.

     scan-window-suspend (default: #f)
          LE scanning window used for active scanning supporting wake from suspend.

     scan-interval-discovery (default: #f)
          LE scanning interval used for active scanning supporting discovery.

     scan-window-discovery (default: #f)
          LE scanning window used for active scanning supporting discovery.

     scan-interval-adv-monitor (default: #f)
          LE scanning interval used for passive scanning supporting the advertisement monitor APIs.

     scan-window-adv-monitor (default: #f)
          LE scanning window used for passive scanning supporting the advertisement monitor APIs.

     scan-interval-connect (default: #f)
          LE scanning interval used for connection establishment.

     scan-window-connect (default: #f)
          LE scanning window used for connection establishment.

     min-connection-interval (default: #f)
          LE default minimum connection interval. This value is superseded by any specific value provided via the Load Connection Parameters interface.

     max-connection-interval (default: #f)
          LE default maximum connection interval. This value is superseded by any specific value provided via the Load Connection Parameters interface.

     connection-latency (default: #f)
          LE default connection latency. This value is superseded by any specific value provided via the Load Connection Parameters interface.

     connection-supervision-timeout (default: #f)
          LE default connection supervision timeout. This value is superseded by any specific value provided via the Load Connection Parameters interface.

     autoconnect-timeout (default: #f)
          LE default autoconnect timeout. This value is superseded by any specific value provided via the Load Connection Parameters interface.

     adv-mon-allowlist-scan-duration (default: 300)
          Allowlist scan duration during interleaving scan. Only used when scanning for ADV monitors. The units are msec.

     adv-mon-no-filter-scan-duration (default: 500)
          No filter scan duration during interleaving scan. Only used when scanning for ADV monitors. The units are msec.

     enable-adv-mon-interleave-scan? (default: #t)
          Enable/Disable Advertisement Monitor interleave scan for power saving.

     cache (default: 'always)
          GATT attribute cache.

          Possible values are:

            * 'always: Always cache attributes even for devices not paired, this is recommended as it is best for interoperability, with more consistent reconnection times and enables proper tracking of notifications for all devices

            * 'yes: Only cache attributes of paired devices

            * 'no: Never cache attributes.

     key-size (default: 0)
          Minimum required Encryption Key Size for accessing secured characteristics.

          Possible values are:

            * 0: Don't care

            * 7 <= N <= 16

     exchange-mtu (default: 517)
          Exchange MTU size. Possible values are:

            * 23 <= N <= 517

     att-channels (default: 3)
          Number of ATT channels. Possible values are:

            * 1: Disables EATT

            * 2 <= N <= 5

     session-mode (default: 'basic)
          AVDTP L2CAP signalling channel mode.

          Possible values are:

            * 'basic: Use L2CAP basic mode

            * 'ertm: Use L2CAP enhanced retransmission mode.

     stream-mode (default: 'basic)
          AVDTP L2CAP transport channel mode.

          Possible values are:

            * 'basic: Use L2CAP basic mode

            * 'streaming: Use L2CAP streaming mode.

     reconnect-uuids (default: '())
          The ReconnectUUIDs defines the set of remote services that should try to be reconnected to in case of a link loss (link supervision timeout). The policy plugin should contain a sane set of values by default, but this list can be overridden here. By setting the list to empty the reconnection feature gets disabled.

          Possible values:

            * '()

            * (list (uuid <uuid-1>) (uuid <uuid-2>) ...).

     reconnect-attempts (default: 7)
          Defines the number of attempts to reconnect after a link lost. Setting the value to 0 disables reconnecting feature.

     reconnect-intervals (default: '(1 2 4 8 16 32 64))
          Defines a list of intervals in seconds to use in between attempts. If the number of attempts defined in RECONNECT-ATTEMPTS is bigger than the list of intervals the last interval is repeated until the last attempt.

     auto-enable? (default: #f)
          Defines option to enable all controllers when they are found. This includes adapters present on start as well as adapters that are plugged in later on.

     resume-delay (default: 2)
          Audio devices that were disconnected due to suspend will be reconnected on resume. RESUME-DELAY determines the delay between when the controller resumes from suspend and a connection attempt is made. A longer delay is better for better co-existence with Wi-Fi. The value is in seconds.

     rssi-sampling-period (default: #xFF)
          Default RSSI Sampling Period. This is used when a client registers an advertisement monitor and leaves the RSSISamplingPeriod unset.

          Possible values are:

            * #x0: Report all advertisements

            * N = #xXX: Report advertisements every N x 100 msec (range: #x01 to #xFE)

            * #xFF: Report only one advertisement per device during monitoring period.

 -- Variable: gnome-keyring-service-type
     This is the type of the service that adds the GNOME Keyring (https://wiki.gnome.org/Projects/GnomeKeyring).  Its value is a gnome-keyring-configuration object (see below).

     This service adds the gnome-keyring package to the system profile and extends PAM with entries using pam_gnome_keyring.so, unlocking a user's login keyring when they log in or setting its password with passwd.

 -- Data Type: gnome-keyring-configuration
     Configuration record for the GNOME Keyring service.

     keyring (default: gnome-keyring)
          The GNOME keyring package to use.

     pam-services
          A list of (SERVICE . KIND) pairs denoting PAM services to extend, where SERVICE is the name of an existing service to extend and KIND is one of login or passwd.

          If login is given, it adds an optional pam_gnome_keyring.so to the auth block without arguments and to the session block with auto_start.  If passwd is given, it adds an optional pam_gnome_keyring.so to the password block without arguments.

          By default, this field contains ``gdm-password'' with the value login and ``passwd'' is with the value passwd.

 -- Variable: seatd-service-type
     seatd (https://sr.ht/~kennylevinsen/seatd/) is a minimal seat management daemon.

     Seat management takes care of mediating access to shared devices (graphics, input), without requiring the applications needing access to be root.

          (append
            (list
             ;; make sure seatd is running
             (service seatd-service-type))

            ;; normally one would want %base-services
            %base-services)

     seatd operates over a UNIX domain socket, with libseat providing the client side of the protocol.  Applications that acquire access to the shared resources via seatd (e.g. sway) need to be able to talk to this socket. This can be achieved by adding the user they run under to the group owning seatd's socket (usually ``seat''), like so:

          (user-account
            (name "alice")
            (group "users")
            (supplementary-groups '("wheel"   ; allow use of sudo, etc.
                                    "seat"    ; seat management
                                    "audio"   ; sound card
                                    "video"   ; video devices such as webcams
                                    "cdrom")) ; the good ol' CD-ROM
            (comment "Bob's sister"))

     Depending on your setup, you will have to not only add regular users, but also system users to this group.  For instance, some greetd greeters require graphics and therefore also need to negotiate with seatd.

 -- Data Type: seatd-configuration
     Configuration record for the seatd daemon service.

     seatd (default: seatd)
          The seatd package to use.

     group (default: "seat")
          Group to own the seatd socket.

     socket (default: "/run/seatd.sock")
          Where to create the seatd socket.

     logfile (default: "/var/log/seatd.log")
          Log file to write to.

     loglevel (default: "error")
          Log level to output logs. Possible values: "silent", "error", "info" and "debug".

Sound Services
--------------

The (gnu services sound) module provides a service to configure the Advanced Linux Sound Architecture (ALSA) system, which makes PulseAudio the preferred ALSA output driver.

 -- Variable: alsa-service-type
     This is the type for the Advanced Linux Sound Architecture (https://alsa-project.org/) (ALSA) system, which generates the /etc/asound.conf configuration file.  The value for this type is a alsa-configuration record as in this example:

          (service alsa-service-type)

     See below for details about alsa-configuration.

 -- Data Type: alsa-configuration
     Data type representing the configuration for alsa-service.

     alsa-plugins (default: ALSA-PLUGINS)
          alsa-plugins package to use.

     pulseaudio? (default: #T)
          Whether ALSA applications should transparently be made to use the PulseAudio (https://www.pulseaudio.org/) sound server.

          Using PulseAudio allows you to run several sound-producing applications at the same time and to individual control them via pavucontrol, among other things.

     extra-options (default: "")
          String to append to the /etc/asound.conf file.

Individual users who want to override the system configuration of ALSA can do it with the ~/.asoundrc file:

     # In guix, we have to specify the absolute path for plugins.
     pcm_type.jack {
       lib "/home/alice/.guix-profile/lib/alsa-lib/libasound_module_pcm_jack.so"
     }

     # Routing ALSA to jack:
     # <http://jackaudio.org/faq/routing_alsa.html>.
     pcm.rawjack {
       type jack
       playback_ports {
         0 system:playback_1
         1 system:playback_2
       }

       capture_ports {
         0 system:capture_1
         1 system:capture_2
       }
     }

     pcm.!default {
       type plug
       slave {
         pcm "rawjack"
       }
     }

See https://www.alsa-project.org/main/index.php/Asoundrc for the details.

 -- Variable: pulseaudio-service-type
     This is the type for the  PulseAudio (https://www.pulseaudio.org/) sound server.  It exists to allow system overrides of the default settings via pulseaudio-configuration, see below.

          This service overrides per-user configuration files.  If you want PulseAudio to honor configuration files in ~/.config/pulse you have to unset the environment variables PULSE_CONFIG and PULSE_CLIENTCONFIG in your ~/.bash_profile.

          This service on its own does not ensure, that the pulseaudio package exists on your machine.  It merely adds configuration files for it, as detailed below.  In the (admittedly unlikely) case, that you find yourself without a pulseaudio package, consider enabling it through the alsa-service-type above.

 -- Data Type: pulseaudio-configuration
     Data type representing the configuration for pulseaudio-service.

     client-conf (default: '())
          List of settings to set in client.conf. Accepts a list of strings or symbol-value pairs.  A string will be inserted as-is with a newline added.  A pair will be formatted as ``key = value'', again with a newline added.

     daemon-conf (default: '((flat-volumes . no)))
          List of settings to set in daemon.conf, formatted just like CLIENT-CONF.

     script-file (default: (file-append pulseaudio "/etc/pulse/default.pa"))
          Script file to use as default.pa.  In case the extra-script-files field below is used, an .include directive pointing to /etc/pulse/default.pa.d is appended to the provided script.

     extra-script-files (default: '())
          A list of file-like objects defining extra PulseAudio scripts to run at the initialization of the pulseaudio daemon, after the main script-file.  The scripts are deployed to the /etc/pulse/default.pa.d directory; they should have the .pa file name extension.  For a reference of the available commands, refer to man pulse-cli-syntax.

     system-script-file (default: (file-append pulseaudio "/etc/pulse/system.pa"))
          Script file to use as system.pa.

     The example below sets the default PulseAudio card profile, the default sink and the default source to use for a old SoundBlaster Audigy sound card:

          (pulseaudio-configuration
           (extra-script-files
            (list (plain-file "audigy.pa"
                              (string-append "\
          set-card-profile alsa_card.pci-0000_01_01.0 \
            output:analog-surround-40+input:analog-mono
          set-default-source alsa_input.pci-0000_01_01.0.analog-mono
          set-default-sink alsa_output.pci-0000_01_01.0.analog-surround-40\n")))))

     Note that pulseaudio-service-type is part of %desktop-services; if your operating system declaration was derived from one of the desktop templates, you'll want to adjust the above example to modify the existing pulseaudio-service-type via modify-services (see modify-services), instead of defining a new one.

 -- Variable: ladspa-service-type
     This service sets the LADSPA_PATH variable, so that programs, which respect it, e.g. PulseAudio, can load LADSPA plugins.

     The following example will setup the service to enable modules from the swh-plugins package:

          (service ladspa-service-type
                   (ladspa-configuration (plugins (list swh-plugins))))

     See http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html for the details.

File Search Services
--------------------

The services in this section populate file databases that let you search for files on your machine.  These services are provided by the (gnu services admin) module.

The first one, file-database-service-type, periodically runs the venerable updatedb command (see Invoking updatedb (GNU Findutils)).  That command populates a database of file names that you can then search with the locate command (see Invoing locate (GNU Findutils)), as in this example:

     locate important-notes.txt

You can enable this service with its default settings by adding this snippet to your operating system services:

     (service file-database-service-type)

This updates the database once a week, excluding files from /gnu/store---these are more usefully handled by guix locate (see Invoking guix locate).  You can of course provide a custom configuration, as described below.

 -- Variable: file-database-service-type
     This is the type of the file database service, which runs updatedb periodically.  Its associated value must be a file-database-configuration record, as described below.

 -- Data Type: file-database-configuration
     Record type for the file-database-service-type configuration, with the following fields:

     package (default: findutils)
          The GNU Findutils package from which the updatedb command is taken.

     schedule (default: %default-file-database-update-schedule)
          String or G-exp denoting an mcron schedule for the periodic updatedb job (see Guile Syntax (GNU mcron)).

     excluded-directories (default %default-file-database-excluded-directories)
          List of regular expressions of directories to ignore when building the file database.  By default, this includes /tmp and /gnu/store; the latter should instead be indexed by guix locate (see Invoking guix locate).  This list is passed to the --prunepaths option of updatedb (see Invoking updatedb (GNU Findutils)).

The second service, package-database-service-type, builds the database used by guix locate, which lets you search for packages that contain a given file (see Invoking guix locate).  The service periodically updates a system-wide database, which will be readily available to anyone running guix locate on the system. To use this service with its default settings, add this snippet to your service list:

     (service package-database-service-type)

This will run guix locate --update once a week.

 -- Variable: package-database-service-type
     This is the service type for periodic guix locate updates (see Invoking guix locate).  Its value must be a package-database-configuration record, as shown below.

 -- Data Type: package-database-configuration
     Data type to configure periodic package database updates.  It has the following fields:

     package (default: guix)
          The Guix package to use.

     schedule (default: %default-package-database-update-schedule)
          String or G-exp denoting an mcron schedule for the periodic guix locate --update job (see Guile Syntax (GNU mcron)).

     method (default: 'store)
          Indexing method for guix locate.  The default value, 'store, yields a more complete database but is relatively expensive in terms of CPU and input/output.

     channels (default: #~%default-channels)
          G-exp denoting the channels to use when updating the database (see Channels).

Database Services
-----------------

The (gnu services databases) module provides the following services.

PostgreSQL
..........

 -- Variable: postgresql-service-type
     The service type for the PostgreSQL database server.  Its value should be a valid postgresql-configuration object, documented below. The following example describes a PostgreSQL service with the default configuration.

          (service postgresql-service-type
                   (postgresql-configuration
                    (postgresql postgresql-10)))

     If the services fails to start, it may be due to an incompatible cluster already present in DATA-DIRECTORY.  Adjust it (or, if you don't need the cluster anymore, delete DATA-DIRECTORY), then restart the service.

     Peer authentication is used by default and the postgres user account has no shell, which prevents the direct execution of psql commands as this user.  To use psql, you can temporarily log in as postgres using a shell, create a PostgreSQL superuser with the same name as one of the system users and then create the associated database.

          sudo -u postgres -s /bin/sh
          createuser --interactive
          createdb $MY_USER_LOGIN      # Replace appropriately.

 -- Data Type: postgresql-configuration
     Data type representing the configuration for the postgresql-service-type.

     postgresql (default: postgresql-10)
          PostgreSQL package to use for the service.

     port (default: 5432)
          Port on which PostgreSQL should listen.

     locale (default: "en_US.utf8")
          Locale to use as the default when creating the database cluster.

     config-file (default: (postgresql-config-file))
          The configuration file to use when running PostgreSQL.  The default behaviour uses the postgresql-config-file record with the default values for the fields.

     log-directory (default: "/var/log/postgresql")
          The directory where pg_ctl output will be written in a file named "pg_ctl.log".  This file can be useful to debug PostgreSQL configuration errors for instance.

     data-directory (default: "/var/lib/postgresql/data")
          Directory in which to store the data.

     extension-packages (default: '())
          Additional extensions are loaded from packages listed in EXTENSION-PACKAGES.  Extensions are available at runtime.  For instance, to create a geographic database using the postgis extension, a user can configure the postgresql-service as in this example:

               (use-package-modules databases geo)

               (operating-system
                 ...
                 ;; postgresql is required to run `psql' but postgis is not required for
                 ;; proper operation.
                 (packages (cons* postgresql %base-packages))
                 (services
                   (cons*
                     (service postgresql-service-type
                              (postgresql-configuration
                               (postgresql postgresql-10)
                               (extension-packages (list postgis))))
                     %base-services)))

          Then the extension becomes visible and you can initialise an empty geographic database in this way:

               psql -U postgres
               > create database postgistest;
               > \connect postgistest;
               > create extension postgis;
               > create extension postgis_topology;

          There is no need to add this field for contrib extensions such as hstore or dblink as they are already loadable by postgresql.  This field is only required to add extensions provided by other packages.

     create-account? (default: #t)
          Whether or not the postgres user and group should be created.

     uid (default: #f)
          Explicitly specify the UID of the postgres daemon account. You normally do not need to specify this, in which case a free UID will be automatically assigned.

          One situation where this option might be useful is if the DATA-DIRECTORY is located on a mounted network share.

     gid (default: #f)
          Explicitly specify the GID of the postgres group.

 -- Data Type: postgresql-config-file
     Data type representing the PostgreSQL configuration file.  As shown in the following example, this can be used to customize the configuration of PostgreSQL.  Note that you can use any G-expression or filename in place of this record, if you already have a configuration file you'd like to use for example.

          (service postgresql-service-type
                   (postgresql-configuration
                    (config-file
                     (postgresql-config-file
                      (log-destination "stderr")
                      (hba-file
                       (plain-file "pg_hba.conf"
                                   "
          local	all	all			trust
          host	all	all	127.0.0.1/32 	md5
          host	all	all	::1/128 	md5"))
                      (extra-config
                       '(("session_preload_libraries"     "auto_explain")
                         ("random_page_cost"              2)
                         ("auto_explain.log_min_duration" "100 ms")
                         ("work_mem"                      "500 MB")
                         ("logging_collector"             #t)
                         ("log_directory"                 "/var/log/postgresql")))))))

     log-destination (default: "syslog")
          The logging method to use for PostgreSQL.  Multiple values are accepted, separated by commas.

     hba-file (default: %default-postgres-hba)
          Filename or G-expression for the host-based authentication configuration.

     ident-file (default: %default-postgres-ident)
          Filename or G-expression for the user name mapping configuration.

     socket-directory (default: "/var/run/postgresql")
          Specifies the directory of the Unix-domain socket(s) on which PostgreSQL is to listen for connections from client applications. If set to "" PostgreSQL does not listen on any Unix-domain sockets, in which case only TCP/IP sockets can be used to connect to the server.

          By default, the #false value means the PostgreSQL default value will be used, which is currently /tmp.

     extra-config (default: '())
          List of additional keys and values to include in the PostgreSQL config file.  Each entry in the list should be a list where the first element is the key, and the remaining elements are the values.

          The values can be numbers, booleans or strings and will be mapped to PostgreSQL parameters types Boolean, String, Numeric, Numeric with Unit and Enumerated described here (https://www.postgresql.org/docs/current/config-setting.html).

 -- Variable: postgresql-role-service-type
     This service allows to create PostgreSQL roles and databases after PostgreSQL service start.  Here is an example of its use.

          (service postgresql-role-service-type
                      (postgresql-role-configuration
                       (roles
                        (list (postgresql-role
                               (name "test")
                               (create-database? #t))))))

     This service can be extended with extra roles, as in this example:

          (service-extension postgresql-role-service-type
                             (const (postgresql-role
                                     (name "alice")
                                     (create-database? #t))))

 -- Data Type: postgresql-role
     PostgreSQL manages database access permissions using the concept of roles.  A role can be thought of as either a database user, or a group of database users, depending on how the role is set up.  Roles can own database objects (for example, tables) and can assign privileges on those objects to other roles to control who has access to which objects.

     name
          The role name.

     permissions (default: '(createdb login))
          The role permissions list.  Supported permissions are bypassrls, createdb, createrole, login, replication and superuser.

     create-database? (default: #f)
          whether to create a database with the same name as the role.

     encoding (default: "UTF8")
          The character set to use for storing text in the database.

     collation (default: "en_US.utf8")
          The string sort order locale setting.

     ctype (default: "en_US.utf8")
          The character classification locale setting.

     template (default: "template1")
          The default template to copy the new database from when creating it. Use "template0" for a pristine database with no system-local modifications.

 -- Data Type: postgresql-role-configuration
     Data type representing the configuration of POSTGRESQL-ROLE-SERVICE-TYPE.

     host (default: "/var/run/postgresql")
          The PostgreSQL host to connect to.

     log (default: "/var/log/postgresql_roles.log")
          File name of the log file.

     roles (default: '())
          The initial PostgreSQL roles to create.

MariaDB/MySQL
.............

 -- Variable: mysql-service-type
     This is the service type for a MySQL or MariaDB database server.  Its value is a mysql-configuration object that specifies which package to use, as well as various settings for the mysqld daemon.

 -- Data Type: mysql-configuration
     Data type representing the configuration of MYSQL-SERVICE-TYPE.

     mysql (default: MARIADB)
          Package object of the MySQL database server, can be either MARIADB or MYSQL.

          For MySQL, a temporary root password will be displayed at activation time. For MariaDB, the root password is empty.

     bind-address (default: "127.0.0.1")
          The IP on which to listen for network connections.  Use "0.0.0.0" to bind to all available network interfaces.

     port (default: 3306)
          TCP port on which the database server listens for incoming connections.

     socket (default: "/run/mysqld/mysqld.sock")
          Socket file to use for local (non-network) connections.

     extra-content (default: "")
          Additional settings for the my.cnf configuration file.

     extra-environment (default: #~'())
          List of environment variables passed to the mysqld process.

     auto-upgrade? (default: #t)
          Whether to automatically run mysql_upgrade after starting the service.  This is necessary to upgrade the system schema after ``major'' updates (such as switching from MariaDB 10.4 to 10.5), but can be disabled if you would rather do that manually.

Memcached
.........

 -- Variable: memcached-service-type
     This is the service type for the Memcached (https://memcached.org/) service, which provides a distributed in memory cache.  The value for the service type is a memcached-configuration object.

     (service memcached-service-type)

 -- Data Type: memcached-configuration
     Data type representing the configuration of memcached.

     memcached (default: memcached)
          The Memcached package to use.

     interfaces (default: '("0.0.0.0"))
          Network interfaces on which to listen.

     tcp-port (default: 11211)
          Port on which to accept connections.

     udp-port (default: 11211)
          Port on which to accept UDP connections on, a value of 0 will disable listening on a UDP socket.

     additional-options (default: '())
          Additional command line options to pass to memcached.

Redis
.....

 -- Variable: redis-service-type
     This is the service type for the Redis (https://redis.io/) key/value store, whose value is a redis-configuration object.

 -- Data Type: redis-configuration
     Data type representing the configuration of redis.

     redis (default: redis)
          The Redis package to use.

     bind (default: "127.0.0.1")
          Network interface on which to listen.

     port (default: 6379)
          Port on which to accept connections on, a value of 0 will disable listening on a TCP socket.

     working-directory (default: "/var/lib/redis")
          Directory in which to store the database and related files.

Mail Services
-------------

The (gnu services mail) module provides Guix service definitions for email services: IMAP, POP3, and LMTP servers, as well as mail transport agents (MTAs).  Lots of acronyms!  These services are detailed in the subsections below.

Dovecot Service
...............

 -- Variable: dovecot-service-type
     Type for the service that runs the Dovecot IMAP/POP3/LMTP mail server, whose value is a <dovecot-configuration> object.

By default, Dovecot does not need much configuration; the default configuration object created by (dovecot-configuration) will suffice if your mail is delivered to ~/Maildir.  A self-signed certificate will be generated for TLS-protected connections, though Dovecot will also listen on cleartext ports by default.  There are a number of options, though, which mail administrators might need to change, and as is the case with other services, Guix allows the system administrator to specify these parameters via a uniform Scheme interface.

For example, to specify that mail is located at maildir~/.mail, one would instantiate the Dovecot service like this:

     (service dovecot-service-type
              (dovecot-configuration
                (mail-location "maildir:~/.mail")))

The available configuration parameters follow.  Each parameter definition is preceded by its type; for example, string-list foo indicates that the foo parameter should be specified as a list of strings.  There is also a way to specify the configuration as a string, if you have an old dovecot.conf file that you want to port over from some other system; see the end for more details.

Available dovecot-configuration fields are:

 -- dovecot-configuration parameter: package dovecot
     The dovecot package.

 -- dovecot-configuration parameter: comma-separated-string-list listen
     A list of IPs or hosts where to listen for connections.  * listens on all IPv4 interfaces, :: listens on all IPv6 interfaces.  If you want to specify non-default ports or anything more complex, customize the address and port fields of the inet-listener of the specific services you are interested in.

 -- dovecot-configuration parameter: protocol-configuration-list protocols
     List of protocols we want to serve.  Available protocols include imap, pop3, and lmtp.

     Available protocol-configuration fields are:

      -- protocol-configuration parameter: string name
          The name of the protocol.

      -- protocol-configuration parameter: string auth-socket-path
          UNIX socket path to the master authentication server to find users. This is used by imap (for shared users) and lda. It defaults to "/var/run/dovecot/auth-userdb".

      -- protocol-configuration parameter: boolean imap-metadata?
          Whether to enable the IMAP METADATA extension as defined in RFC 5464 (https://tools.ietf.org/html/rfc5464), which provides a means for clients to set and retrieve per-mailbox, per-user metadata and annotations over IMAP.

          If this is #t, you must also specify a dictionary via the mail-attribute-dict setting.

          Defaults to #f.

      -- protocol-configuration parameter: space-separated-string-list managesieve-notify-capabilities
          Which NOTIFY capabilities to report to clients that first connect to the ManageSieve service, before authentication.  These may differ from the capabilities offered to authenticated users.  If this field is left empty, report what the Sieve interpreter supports by default.

          Defaults to '().

      -- protocol-configuration parameter: space-separated-string-list managesieve-sieve-capability
          Which SIEVE capabilities to report to clients that first connect to the ManageSieve service, before authentication.  These may differ from the capabilities offered to authenticated users.  If this field is left empty, report what the Sieve interpreter supports by default.

          Defaults to '().

      -- protocol-configuration parameter: space-separated-string-list mail-plugins
          Space separated list of plugins to load.

      -- protocol-configuration parameter: non-negative-integer mail-max-userip-connections
          Maximum number of IMAP connections allowed for a user from each IP address.  NOTE: The username is compared case-sensitively. Defaults to 10.

 -- dovecot-configuration parameter: service-configuration-list services
     List of services to enable.  Available services include imap, imap-login, pop3, pop3-login, auth, and lmtp.

     Available service-configuration fields are:

      -- service-configuration parameter: string kind
          The service kind.  Valid values include director, imap-login, pop3-login, lmtp, imap, pop3, auth, auth-worker, dict, tcpwrap, quota-warning, or anything else.

      -- service-configuration parameter: listener-configuration-list listeners
          Listeners for the service.  A listener is either a unix-listener-configuration, a fifo-listener-configuration, or an inet-listener-configuration. Defaults to '().

          Available unix-listener-configuration fields are:

           -- unix-listener-configuration parameter: string path
               Path to the file, relative to base-dir field.  This is also used as the section name.

           -- unix-listener-configuration parameter: string mode
               The access mode for the socket. Defaults to "0600".

           -- unix-listener-configuration parameter: string user
               The user to own the socket. Defaults to "".

           -- unix-listener-configuration parameter: string group
               The group to own the socket. Defaults to "".

          Available fifo-listener-configuration fields are:

           -- fifo-listener-configuration parameter: string path
               Path to the file, relative to base-dir field.  This is also used as the section name.

           -- fifo-listener-configuration parameter: string mode
               The access mode for the socket. Defaults to "0600".

           -- fifo-listener-configuration parameter: string user
               The user to own the socket. Defaults to "".

           -- fifo-listener-configuration parameter: string group
               The group to own the socket. Defaults to "".

          Available inet-listener-configuration fields are:

           -- inet-listener-configuration parameter: string protocol
               The protocol to listen for.

           -- inet-listener-configuration parameter: string address
               The address on which to listen, or empty for all addresses. Defaults to "".

           -- inet-listener-configuration parameter: non-negative-integer port
               The port on which to listen.

           -- inet-listener-configuration parameter: boolean ssl?
               Whether to use SSL for this service; yes, no, or required. Defaults to #t.

      -- service-configuration parameter: non-negative-integer client-limit
          Maximum number of simultaneous client connections per process.  Once this number of connections is received, the next incoming connection will prompt Dovecot to spawn another process.  If set to 0, default-client-limit is used instead.

          Defaults to 0.

      -- service-configuration parameter: non-negative-integer service-count
          Number of connections to handle before starting a new process. Typically the only useful values are 0 (unlimited) or 1.  1 is more secure, but 0 is faster.  <doc/wiki/LoginProcess.txt>. Defaults to 1.

      -- service-configuration parameter: non-negative-integer process-limit
          Maximum number of processes that can exist for this service.  If set to 0, default-process-limit is used instead.

          Defaults to 0.

      -- service-configuration parameter: non-negative-integer process-min-avail
          Number of processes to always keep waiting for more connections. Defaults to 0.

      -- service-configuration parameter: non-negative-integer vsz-limit
          If you set service-count 0, you probably need to grow this. Defaults to 256000000.

 -- dovecot-configuration parameter: dict-configuration dict
     Dict configuration, as created by the dict-configuration constructor.

     Available dict-configuration fields are:

      -- dict-configuration parameter: free-form-fields entries
          A list of key-value pairs that this dict should hold. Defaults to '().

 -- dovecot-configuration parameter: passdb-configuration-list passdbs
     A list of passdb configurations, each one created by the passdb-configuration constructor.

     Available passdb-configuration fields are:

      -- passdb-configuration parameter: string driver
          The driver that the passdb should use.  Valid values include pam, passwd, shadow, bsdauth, and static. Defaults to "pam".

      -- passdb-configuration parameter: space-separated-string-list args
          Space separated list of arguments to the passdb driver. Defaults to "".

 -- dovecot-configuration parameter: userdb-configuration-list userdbs
     List of userdb configurations, each one created by the userdb-configuration constructor.

     Available userdb-configuration fields are:

      -- userdb-configuration parameter: string driver
          The driver that the userdb should use.  Valid values include passwd and static. Defaults to "passwd".

      -- userdb-configuration parameter: space-separated-string-list args
          Space separated list of arguments to the userdb driver. Defaults to "".

      -- userdb-configuration parameter: free-form-args override-fields
          Override fields from passwd. Defaults to '().

 -- dovecot-configuration parameter: plugin-configuration plugin-configuration
     Plug-in configuration, created by the plugin-configuration constructor.

 -- dovecot-configuration parameter: list-of-namespace-configuration namespaces
     List of namespaces.  Each item in the list is created by the namespace-configuration constructor.

     Available namespace-configuration fields are:

      -- namespace-configuration parameter: string name
          Name for this namespace.

      -- namespace-configuration parameter: string type
          Namespace type: private, shared or public. Defaults to "private".

      -- namespace-configuration parameter: string separator
          Hierarchy separator to use.  You should use the same separator for all namespaces or some clients get confused.  / is usually a good one.  The default however depends on the underlying mail storage format. Defaults to "".

      -- namespace-configuration parameter: string prefix
          Prefix required to access this namespace.  This needs to be different for all namespaces.  For example Public/. Defaults to "".

      -- namespace-configuration parameter: string location
          Physical location of the mailbox. This is in the same format as mail_location, which is also the default for it. Defaults to "".

      -- namespace-configuration parameter: boolean inbox?
          There can be only one INBOX, and this setting defines which namespace has it. Defaults to #f.

      -- namespace-configuration parameter: boolean hidden?
          If namespace is hidden, it's not advertised to clients via NAMESPACE extension.  You'll most likely also want to set list? #f.  This is mostly useful when converting from another server with different namespaces which you want to deprecate but still keep working.  For example you can create hidden namespaces with prefixes ~/mail/, ~%u/mail/ and mail/. Defaults to #f.

      -- namespace-configuration parameter: boolean list?
          Show the mailboxes under this namespace with the LIST command.  This makes the namespace visible for clients that do not support the NAMESPACE extension.  The special children value lists child mailboxes, but hides the namespace prefix. Defaults to #t.

      -- namespace-configuration parameter: boolean subscriptions?
          Namespace handles its own subscriptions.  If set to #f, the parent namespace handles them.  The empty prefix should always have this as #t). Defaults to #t.

      -- namespace-configuration parameter: mailbox-configuration-list mailboxes
          List of predefined mailboxes in this namespace. Defaults to '().

          Available mailbox-configuration fields are:

           -- mailbox-configuration parameter: string name
               Name for this mailbox.

           -- mailbox-configuration parameter: string auto
               create will automatically create this mailbox. subscribe will both create and subscribe to the mailbox. Defaults to "no".

           -- mailbox-configuration parameter: space-separated-string-list special-use
               List of IMAP SPECIAL-USE attributes as specified by RFC 6154. Valid values are \All, \Archive, \Drafts, \Flagged, \Junk, \Sent, and \Trash. Defaults to '().

 -- dovecot-configuration parameter: file-name base-dir
     Base directory where to store runtime data. Defaults to "/var/run/dovecot/".

 -- dovecot-configuration parameter: string login-greeting
     Greeting message for clients. Defaults to "Dovecot ready.".

 -- dovecot-configuration parameter: space-separated-string-list login-trusted-networks
     List of trusted network ranges.  Connections from these IPs are allowed to override their IP addresses and ports (for logging and for authentication checks).  disable-plaintext-auth is also ignored for these networks.  Typically you would specify your IMAP proxy servers here. Defaults to '().

 -- dovecot-configuration parameter: space-separated-string-list login-access-sockets
     List of login access check sockets (e.g. tcpwrap). Defaults to '().

 -- dovecot-configuration parameter: boolean verbose-proctitle?
     Show more verbose process titles (in ps).  Currently shows user name and IP address.  Useful for seeing who is actually using the IMAP processes (e.g. shared mailboxes or if the same uid is used for multiple accounts). Defaults to #f.

 -- dovecot-configuration parameter: boolean shutdown-clients?
     Should all processes be killed when Dovecot master process shuts down. Setting this to #f means that Dovecot can be upgraded without forcing existing client connections to close (although that could also be a problem if the upgrade is e.g. due to a security fix). Defaults to #t.

 -- dovecot-configuration parameter: non-negative-integer doveadm-worker-count
     If non-zero, run mail commands via this many connections to doveadm server, instead of running them directly in the same process. Defaults to 0.

 -- dovecot-configuration parameter: string doveadm-socket-path
     UNIX socket or host:port used for connecting to doveadm server. Defaults to "doveadm-server".

 -- dovecot-configuration parameter: space-separated-string-list import-environment
     List of environment variables that are preserved on Dovecot startup and passed down to all of its child processes.  You can also give key=value pairs to always set specific settings.

 -- dovecot-configuration parameter: boolean disable-plaintext-auth?
     Disable LOGIN command and all other plaintext authentications unless SSL/TLS is used (LOGINDISABLED capability).  Note that if the remote IP matches the local IP (i.e. you're connecting from the same computer), the connection is considered secure and plaintext authentication is allowed.  See also ssl=required setting. Defaults to #t.

 -- dovecot-configuration parameter: non-negative-integer auth-cache-size
     Authentication cache size (e.g. #e10e6).  0 means it's disabled. Note that bsdauth, PAM and vpopmail require cache-key to be set for caching to be used. Defaults to 0.

 -- dovecot-configuration parameter: string auth-cache-ttl
     Time to live for cached data.  After TTL expires the cached record is no longer used, *except* if the main database lookup returns internal failure.  We also try to handle password changes automatically: If user's previous authentication was successful, but this one wasn't, the cache isn't used.  For now this works only with plaintext authentication. Defaults to "1 hour".

 -- dovecot-configuration parameter: string auth-cache-negative-ttl
     TTL for negative hits (user not found, password mismatch). 0 disables caching them completely. Defaults to "1 hour".

 -- dovecot-configuration parameter: space-separated-string-list auth-realms
     List of realms for SASL authentication mechanisms that need them. You can leave it empty if you don't want to support multiple realms. Many clients simply use the first one listed here, so keep the default realm first. Defaults to '().

 -- dovecot-configuration parameter: string auth-default-realm
     Default realm/domain to use if none was specified.  This is used for both SASL realms and appending @domain to username in plaintext logins. Defaults to "".

 -- dovecot-configuration parameter: string auth-username-chars
     List of allowed characters in username.  If the user-given username contains a character not listed in here, the login automatically fails. This is just an extra check to make sure user can't exploit any potential quote escaping vulnerabilities with SQL/LDAP databases.  If you want to allow all characters, set this value to empty. Defaults to "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@".

 -- dovecot-configuration parameter: string auth-username-translation
     Username character translations before it's looked up from databases.  The value contains series of from -> to characters.  For example #@/@ means that # and / characters are translated to @. Defaults to "".

 -- dovecot-configuration parameter: string auth-username-format
     Username formatting before it's looked up from databases.  You can use the standard variables here, e.g. %Lu would lowercase the username, %n would drop away the domain if it was given, or %n-AT-%d would change the @ into -AT-.  This translation is done after auth-username-translation changes. Defaults to "%Lu".

 -- dovecot-configuration parameter: string auth-master-user-separator
     If you want to allow master users to log in by specifying the master username within the normal username string (i.e. not using SASL mechanism's support for it), you can specify the separator character here.  The format is then <username><separator><master username>. UW-IMAP uses * as the separator, so that could be a good choice. Defaults to "".

 -- dovecot-configuration parameter: string auth-anonymous-username
     Username to use for users logging in with ANONYMOUS SASL mechanism. Defaults to "anonymous".

 -- dovecot-configuration parameter: non-negative-integer auth-worker-max-count
     Maximum number of dovecot-auth worker processes.  They're used to execute blocking passdb and userdb queries (e.g. MySQL and PAM). They're automatically created and destroyed as needed. Defaults to 30.

 -- dovecot-configuration parameter: string auth-gssapi-hostname
     Host name to use in GSSAPI principal names.  The default is to use the name returned by gethostname().  Use $ALL (with quotes) to allow all keytab entries. Defaults to "".

 -- dovecot-configuration parameter: string auth-krb5-keytab
     Kerberos keytab to use for the GSSAPI mechanism.  Will use the system default (usually /etc/krb5.keytab) if not specified.  You may need to change the auth service to run as root to be able to read this file. Defaults to "".

 -- dovecot-configuration parameter: boolean auth-use-winbind?
     Do NTLM and GSS-SPNEGO authentication using Samba's winbind daemon and ntlm-auth helper. <doc/wiki/Authentication/Mechanisms/Winbind.txt>. Defaults to #f.

 -- dovecot-configuration parameter: file-name auth-winbind-helper-path
     Path for Samba's ntlm-auth helper binary. Defaults to "/usr/bin/ntlm_auth".

 -- dovecot-configuration parameter: string auth-failure-delay
     Time to delay before replying to failed authentications. Defaults to "2 secs".

 -- dovecot-configuration parameter: boolean auth-ssl-require-client-cert?
     Require a valid SSL client certificate or the authentication fails. Defaults to #f.

 -- dovecot-configuration parameter: boolean auth-ssl-username-from-cert?
     Take the username from client's SSL certificate, using X509_NAME_get_text_by_NID() which returns the subject's DN's CommonName. Defaults to #f.

 -- dovecot-configuration parameter: space-separated-string-list auth-mechanisms
     List of wanted authentication mechanisms.  Supported mechanisms are: plain, login, digest-md5, cram-md5, ntlm, rpa, apop, anonymous, gssapi, otp, skey, and gss-spnego.  NOTE: See also disable-plaintext-auth setting.

 -- dovecot-configuration parameter: space-separated-string-list director-servers
     List of IPs or hostnames to all director servers, including ourself. Ports can be specified as ip:port.  The default port is the same as what director service's inet-listener is using. Defaults to '().

 -- dovecot-configuration parameter: space-separated-string-list director-mail-servers
     List of IPs or hostnames to all backend mail servers.  Ranges are allowed too, like 10.0.0.10-10.0.0.30. Defaults to '().

 -- dovecot-configuration parameter: string director-user-expire
     How long to redirect users to a specific server after it no longer has any connections. Defaults to "15 min".

 -- dovecot-configuration parameter: string director-username-hash
     How the username is translated before being hashed.  Useful values include %Ln if user can log in with or without @domain, %Ld if mailboxes are shared within domain. Defaults to "%Lu".

 -- dovecot-configuration parameter: string log-path
     Log file to use for error messages.  syslog logs to syslog, /dev/stderr logs to stderr. Defaults to "syslog".

 -- dovecot-configuration parameter: string info-log-path
     Log file to use for informational messages.  Defaults to log-path. Defaults to "".

 -- dovecot-configuration parameter: string debug-log-path
     Log file to use for debug messages.  Defaults to info-log-path. Defaults to "".

 -- dovecot-configuration parameter: string syslog-facility
     Syslog facility to use if you're logging to syslog.  Usually if you don't want to use mail, you'll use local0..local7.  Also other standard facilities are supported. Defaults to "mail".

 -- dovecot-configuration parameter: boolean auth-verbose?
     Log unsuccessful authentication attempts and the reasons why they failed. Defaults to #f.

 -- dovecot-configuration parameter: string auth-verbose-passwords
     In case of password mismatches, log the attempted password.  Valid values are no, plain and sha1.  sha1 can be useful for detecting brute force password attempts vs.  user simply trying the same password over and over again.  You can also truncate the value to n chars by appending ":n" (e.g. sha1:6). Defaults to "no".

 -- dovecot-configuration parameter: boolean auth-debug?
     Even more verbose logging for debugging purposes.  Shows for example SQL queries. Defaults to #f.

 -- dovecot-configuration parameter: boolean auth-debug-passwords?
     In case of password mismatches, log the passwords and used scheme so the problem can be debugged.  Enabling this also enables auth-debug. Defaults to #f.

 -- dovecot-configuration parameter: boolean mail-debug?
     Enable mail process debugging.  This can help you figure out why Dovecot isn't finding your mails. Defaults to #f.

 -- dovecot-configuration parameter: boolean verbose-ssl?
     Show protocol level SSL errors. Defaults to #f.

 -- dovecot-configuration parameter: string log-timestamp
     Prefix for each line written to log file.  % codes are in strftime(3) format. Defaults to "\"%b %d %H:%M:%S \"".

 -- dovecot-configuration parameter: space-separated-string-list login-log-format-elements
     List of elements we want to log.  The elements which have a non-empty variable value are joined together to form a comma-separated string.

 -- dovecot-configuration parameter: string login-log-format
     Login log format.  %s contains login-log-format-elements string, %$ contains the data we want to log. Defaults to "%$: %s".

 -- dovecot-configuration parameter: string mail-log-prefix
     Log prefix for mail processes.  See doc/wiki/Variables.txt for list of possible variables you can use. Defaults to "\"%s(%u)<%{pid}><%{session}>: \"".

 -- dovecot-configuration parameter: string deliver-log-format
     Format to use for logging mail deliveries.  You can use variables:

     %$
          Delivery status message (e.g. saved to INBOX)

     %m
          Message-ID

     %s
          Subject

     %f
          From address

     %p
          Physical size

     %w
          Virtual size.

     Defaults to "msgid=%m: %$".

 -- dovecot-configuration parameter: string mail-location
     Location for users' mailboxes.  The default is empty, which means that Dovecot tries to find the mailboxes automatically.  This won't work if the user doesn't yet have any mail, so you should explicitly tell Dovecot the full location.

     If you're using mbox, giving a path to the INBOX file (e.g. /var/mail/%u) isn't enough.  You'll also need to tell Dovecot where the other mailboxes are kept.  This is called the root mail directory, and it must be the first path given in the mail-location setting.

     There are a few special variables you can use, e.g.:

     %u
          username

     %n
          user part in user@domain, same as %u if there's no domain

     %d
          domain part in user@domain, empty if there's no domain

     %h
          home director

     See doc/wiki/Variables.txt for full list.  Some examples:

     maildir:~/Maildir

     mbox:~/mail:INBOX=/var/mail/%u

     mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%

     Defaults to "".

 -- dovecot-configuration parameter: string mail-uid
     System user and group used to access mails.  If you use multiple, userdb can override these by returning uid or gid fields.  You can use either numbers or names.  <doc/wiki/UserIds.txt>. Defaults to "".

 -- dovecot-configuration parameter: string mail-gid

     Defaults to "".

 -- dovecot-configuration parameter: string mail-privileged-group
     Group to enable temporarily for privileged operations.  Currently this is used only with INBOX when either its initial creation or dotlocking fails.  Typically this is set to "mail" to give access to /var/mail. Defaults to "".

 -- dovecot-configuration parameter: string mail-access-groups
     Grant access to these supplementary groups for mail processes. Typically these are used to set up access to shared mailboxes.  Note that it may be dangerous to set these if users can create symlinks (e.g. if mail group is set here, ln -s /var/mail ~/mail/var could allow a user to delete others' mailboxes, or ln -s /secret/shared/box ~/mail/mybox would allow reading it).  Defaults to "".

 -- dovecot-configuration parameter: string mail-attribute-dict
     The location of a dictionary used to store IMAP METADATA as defined by RFC 5464 (https://tools.ietf.org/html/rfc5464).

     The IMAP METADATA commands are available only if the ``imap'' protocol configuration's imap-metadata? field is #t.

     Defaults to "".

 -- dovecot-configuration parameter: boolean mail-full-filesystem-access?
     Allow full file system access to clients.  There's no access checks other than what the operating system does for the active UID/GID.  It works with both maildir and mboxes, allowing you to prefix mailboxes names with e.g. /path/ or ~user/. Defaults to #f.

 -- dovecot-configuration parameter: boolean mmap-disable?
     Don't use mmap() at all.  This is required if you store indexes to shared file systems (NFS or clustered file system). Defaults to #f.

 -- dovecot-configuration parameter: boolean dotlock-use-excl?
     Rely on O_EXCL to work when creating dotlock files.  NFS supports O_EXCL since version 3, so this should be safe to use nowadays by default. Defaults to #t.

 -- dovecot-configuration parameter: string mail-fsync
     When to use fsync() or fdatasync() calls:

     optimized
          Whenever necessary to avoid losing important data

     always
          Useful with e.g. NFS when write()s are delayed

     never
          Never use it (best performance, but crashes can lose data).

     Defaults to "optimized".

 -- dovecot-configuration parameter: boolean mail-nfs-storage?
     Mail storage exists in NFS.  Set this to yes to make Dovecot flush NFS caches whenever needed.  If you're using only a single mail server this isn't needed. Defaults to #f.

 -- dovecot-configuration parameter: boolean mail-nfs-index?
     Mail index files also exist in NFS.  Setting this to yes requires mmap-disable? #t and fsync-disable? #f. Defaults to #f.

 -- dovecot-configuration parameter: string lock-method
     Locking method for index files.  Alternatives are fcntl, flock and dotlock.  Dotlocking uses some tricks which may create more disk I/O than other locking methods.  NFS users: flock doesn't work, remember to change mmap-disable. Defaults to "fcntl".

 -- dovecot-configuration parameter: file-name mail-temp-dir
     Directory in which LDA/LMTP temporarily stores incoming mails >128 kB. Defaults to "/tmp".

 -- dovecot-configuration parameter: non-negative-integer first-valid-uid
     Valid UID range for users.  This is mostly to make sure that users can't log in as daemons or other system users.  Note that denying root logins is hardcoded to dovecot binary and can't be done even if first-valid-uid is set to 0. Defaults to 500.

 -- dovecot-configuration parameter: non-negative-integer last-valid-uid

     Defaults to 0.

 -- dovecot-configuration parameter: non-negative-integer first-valid-gid
     Valid GID range for users.  Users having non-valid GID as primary group ID aren't allowed to log in.  If user belongs to supplementary groups with non-valid GIDs, those groups are not set. Defaults to 1.

 -- dovecot-configuration parameter: non-negative-integer last-valid-gid

     Defaults to 0.

 -- dovecot-configuration parameter: non-negative-integer mail-max-keyword-length
     Maximum allowed length for mail keyword name.  It's only forced when trying to create new keywords. Defaults to 50.

 -- dovecot-configuration parameter: colon-separated-file-name-list valid-chroot-dirs
     List of directories under which chrooting is allowed for mail processes (i.e. /var/mail will allow chrooting to /var/mail/foo/bar too).  This setting doesn't affect login-chroot mail-chroot or auth chroot settings.  If this setting is empty, /./ in home dirs are ignored.  WARNING: Never add directories here which local users can modify, that may lead to root exploit.  Usually this should be done only if you don't allow shell access for users. <doc/wiki/Chrooting.txt>. Defaults to '().

 -- dovecot-configuration parameter: string mail-chroot
     Default chroot directory for mail processes.  This can be overridden for specific users in user database by giving /./ in user's home directory (e.g. /home/./user chroots into /home).  Note that usually there is no real need to do chrooting, Dovecot doesn't allow users to access files outside their mail directory anyway.  If your home directories are prefixed with the chroot directory, append /. to mail-chroot.  <doc/wiki/Chrooting.txt>. Defaults to "".

 -- dovecot-configuration parameter: file-name auth-socket-path
     UNIX socket path to master authentication server to find users. This is used by imap (for shared users) and lda. Defaults to "/var/run/dovecot/auth-userdb".

 -- dovecot-configuration parameter: file-name mail-plugin-dir
     Directory where to look up mail plugins. Defaults to "/usr/lib/dovecot".

 -- dovecot-configuration parameter: space-separated-string-list mail-plugins
     List of plugins to load for all services.  Plugins specific to IMAP, LDA, etc. are added to this list in their own .conf files. Defaults to '().

 -- dovecot-configuration parameter: non-negative-integer mail-cache-min-mail-count
     The minimum number of mails in a mailbox before updates are done to cache file.  This allows optimizing Dovecot's behavior to do less disk writes at the cost of more disk reads. Defaults to 0.

 -- dovecot-configuration parameter: string mailbox-idle-check-interval
     When IDLE command is running, mailbox is checked once in a while to see if there are any new mails or other changes.  This setting defines the minimum time to wait between those checks.  Dovecot can also use dnotify, inotify and kqueue to find out immediately when changes occur. Defaults to "30 secs".

 -- dovecot-configuration parameter: boolean mail-save-crlf?
     Save mails with CR+LF instead of plain LF.  This makes sending those mails take less CPU, especially with sendfile() syscall with Linux and FreeBSD.  But it also creates a bit more disk I/O which may just make it slower.  Also note that if other software reads the mboxes/maildirs, they may handle the extra CRs wrong and cause problems. Defaults to #f.

 -- dovecot-configuration parameter: boolean maildir-stat-dirs?
     By default LIST command returns all entries in maildir beginning with a dot.  Enabling this option makes Dovecot return only entries which are directories.  This is done by stat()ing each entry, so it causes more disk I/O. (For systems setting struct dirent->d_type this check is free and it's done always regardless of this setting). Defaults to #f.

 -- dovecot-configuration parameter: boolean maildir-copy-with-hardlinks?
     When copying a message, do it with hard links whenever possible. This makes the performance much better, and it's unlikely to have any side effects. Defaults to #t.

 -- dovecot-configuration parameter: boolean maildir-very-dirty-syncs?
     Assume Dovecot is the only MUA accessing Maildir: Scan cur/ directory only when its mtime changes unexpectedly or when we can't find the mail otherwise. Defaults to #f.

 -- dovecot-configuration parameter: space-separated-string-list mbox-read-locks
     Which locking methods to use for locking mbox.  There are four available:

     dotlock
          Create <mailbox>.lock file.  This is the oldest and most NFS-safe solution.  If you want to use /var/mail/ like directory, the users will need write access to that directory.

     dotlock-try
          Same as dotlock, but if it fails because of permissions or because there isn't enough disk space, just skip it.

     fcntl
          Use this if possible.  Works with NFS too if lockd is used.

     flock
          May not exist in all systems.  Doesn't work with NFS.

     lockf
          May not exist in all systems.  Doesn't work with NFS.

     You can use multiple locking methods; if you do the order they're declared in is important to avoid deadlocks if other MTAs/MUAs are using multiple locking methods as well.  Some operating systems don't allow using some of them simultaneously.

 -- dovecot-configuration parameter: space-separated-string-list mbox-write-locks

 -- dovecot-configuration parameter: string mbox-lock-timeout
     Maximum time to wait for lock (all of them) before aborting. Defaults to "5 mins".

 -- dovecot-configuration parameter: string mbox-dotlock-change-timeout
     If dotlock exists but the mailbox isn't modified in any way, override the lock file after this much time. Defaults to "2 mins".

 -- dovecot-configuration parameter: boolean mbox-dirty-syncs?
     When mbox changes unexpectedly we have to fully read it to find out what changed.  If the mbox is large this can take a long time.  Since the change is usually just a newly appended mail, it'd be faster to simply read the new mails.  If this setting is enabled, Dovecot does this but still safely fallbacks to re-reading the whole mbox file whenever something in mbox isn't how it's expected to be.  The only real downside to this setting is that if some other MUA changes message flags, Dovecot doesn't notice it immediately.  Note that a full sync is done with SELECT, EXAMINE, EXPUNGE and CHECK commands. Defaults to #t.

 -- dovecot-configuration parameter: boolean mbox-very-dirty-syncs?
     Like mbox-dirty-syncs, but don't do full syncs even with SELECT, EXAMINE, EXPUNGE or CHECK commands.  If this is set, mbox-dirty-syncs is ignored. Defaults to #f.

 -- dovecot-configuration parameter: boolean mbox-lazy-writes?
     Delay writing mbox headers until doing a full write sync (EXPUNGE and CHECK commands and when closing the mailbox).  This is especially useful for POP3 where clients often delete all mails.  The downside is that our changes aren't immediately visible to other MUAs. Defaults to #t.

 -- dovecot-configuration parameter: non-negative-integer mbox-min-index-size
     If mbox size is smaller than this (e.g. 100k), don't write index files.  If an index file already exists it's still read, just not updated. Defaults to 0.

 -- dovecot-configuration parameter: non-negative-integer mdbox-rotate-size
     Maximum dbox file size until it's rotated. Defaults to 10000000.

 -- dovecot-configuration parameter: string mdbox-rotate-interval
     Maximum dbox file age until it's rotated.  Typically in days.  Day begins from midnight, so 1d = today, 2d = yesterday, etc.  0 = check disabled. Defaults to "1d".

 -- dovecot-configuration parameter: boolean mdbox-preallocate-space?
     When creating new mdbox files, immediately preallocate their size to mdbox-rotate-size.  This setting currently works only in Linux with some file systems (ext4, xfs). Defaults to #f.

 -- dovecot-configuration parameter: string mail-attachment-dir
     sdbox and mdbox support saving mail attachments to external files, which also allows single instance storage for them.  Other backends don't support this for now.

     WARNING: This feature hasn't been tested much yet.  Use at your own risk.

     Directory root where to store mail attachments.  Disabled, if empty. Defaults to "".

 -- dovecot-configuration parameter: non-negative-integer mail-attachment-min-size
     Attachments smaller than this aren't saved externally.  It's also possible to write a plugin to disable saving specific attachments externally. Defaults to 128000.

 -- dovecot-configuration parameter: string mail-attachment-fs
     File system backend to use for saving attachments:

     posix
          No SiS done by Dovecot (but this might help FS's own deduplication)

     sis posix
          SiS with immediate byte-by-byte comparison during saving

     sis-queue posix
          SiS with delayed comparison and deduplication.

     Defaults to "sis posix".

 -- dovecot-configuration parameter: string mail-attachment-hash
     Hash format to use in attachment filenames.  You can add any text and variables: %{md4}, %{md5}, %{sha1}, %{sha256}, %{sha512}, %{size}.  Variables can be truncated, e.g. %{sha256:80} returns only first 80 bits. Defaults to "%{sha1}".

 -- dovecot-configuration parameter: non-negative-integer default-process-limit

     Defaults to 100.

 -- dovecot-configuration parameter: non-negative-integer default-client-limit

     Defaults to 1000.

 -- dovecot-configuration parameter: non-negative-integer default-vsz-limit
     Default VSZ (virtual memory size) limit for service processes. This is mainly intended to catch and kill processes that leak memory before they eat up everything. Defaults to 256000000.

 -- dovecot-configuration parameter: string default-login-user
     Login user is internally used by login processes.  This is the most untrusted user in Dovecot system.  It shouldn't have access to anything at all. Defaults to "dovenull".

 -- dovecot-configuration parameter: string default-internal-user
     Internal user is used by unprivileged processes.  It should be separate from login user, so that login processes can't disturb other processes. Defaults to "dovecot".

 -- dovecot-configuration parameter: string ssl?
     SSL/TLS support: yes, no, required.  <doc/wiki/SSL.txt>. Defaults to "required".

 -- dovecot-configuration parameter: string ssl-cert
     PEM encoded X.509 SSL/TLS certificate (public key). Defaults to "</etc/dovecot/default.pem".

 -- dovecot-configuration parameter: string ssl-key
     PEM encoded SSL/TLS private key.  The key is opened before dropping root privileges, so keep the key file unreadable by anyone but root. Defaults to "</etc/dovecot/private/default.pem".

 -- dovecot-configuration parameter: string ssl-key-password
     If key file is password protected, give the password here. Alternatively give it when starting dovecot with -p parameter.  Since this file is often world-readable, you may want to place this setting instead to a different. Defaults to "".

 -- dovecot-configuration parameter: string ssl-ca
     PEM encoded trusted certificate authority.  Set this only if you intend to use ssl-verify-client-cert? #t.  The file should contain the CA certificate(s) followed by the matching CRL(s).  (e.g. ssl-ca </etc/ssl/certs/ca.pem). Defaults to "".

 -- dovecot-configuration parameter: boolean ssl-require-crl?
     Require that CRL check succeeds for client certificates. Defaults to #t.

 -- dovecot-configuration parameter: boolean ssl-verify-client-cert?
     Request client to send a certificate.  If you also want to require it, set auth-ssl-require-client-cert? #t in auth section. Defaults to #f.

 -- dovecot-configuration parameter: string ssl-cert-username-field
     Which field from certificate to use for username.  commonName and x500UniqueIdentifier are the usual choices.  You'll also need to set auth-ssl-username-from-cert? #t. Defaults to "commonName".

 -- dovecot-configuration parameter: string ssl-min-protocol
     Minimum SSL protocol version to accept. Defaults to "TLSv1".

 -- dovecot-configuration parameter: string ssl-cipher-list
     SSL ciphers to use. Defaults to "ALL:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW@STRENGTH".

 -- dovecot-configuration parameter: string ssl-crypto-device
     SSL crypto device to use, for valid values run "openssl engine". Defaults to "".

 -- dovecot-configuration parameter: string postmaster-address
     Address to use when sending rejection mails. %d expands to recipient domain. Defaults to "postmaster@%d".

 -- dovecot-configuration parameter: string hostname
     Hostname to use in various parts of sent mails (e.g. in Message-Id) and in LMTP replies.  Default is the system's real hostname@domain. Defaults to "".

 -- dovecot-configuration parameter: boolean quota-full-tempfail?
     If user is over quota, return with temporary failure instead of bouncing the mail. Defaults to #f.

 -- dovecot-configuration parameter: file-name sendmail-path
     Binary to use for sending mails. Defaults to "/usr/sbin/sendmail".

 -- dovecot-configuration parameter: string submission-host
     If non-empty, send mails via this SMTP host[:port] instead of sendmail. Defaults to "".

 -- dovecot-configuration parameter: string rejection-subject
     Subject: header to use for rejection mails.  You can use the same variables as for rejection-reason below. Defaults to "Rejected: %s".

 -- dovecot-configuration parameter: string rejection-reason
     Human readable error message for rejection mails.  You can use variables:

     %n
          CRLF

     %r
          reason

     %s
          original subject

     %t
          recipient

     Defaults to "Your message to <%t> was automatically rejected:%n%r".

 -- dovecot-configuration parameter: string recipient-delimiter
     Delimiter character between local-part and detail in email address. Defaults to "+".

 -- dovecot-configuration parameter: string lda-original-recipient-header
     Header where the original recipient address (SMTP's RCPT TO: address) is taken from if not available elsewhere.  With dovecot-lda -a parameter overrides this.  A commonly used header for this is X-Original-To. Defaults to "".

 -- dovecot-configuration parameter: boolean lda-mailbox-autocreate?
     Should saving a mail to a nonexistent mailbox automatically create it?. Defaults to #f.

 -- dovecot-configuration parameter: boolean lda-mailbox-autosubscribe?
     Should automatically created mailboxes be also automatically subscribed?. Defaults to #f.

 -- dovecot-configuration parameter: non-negative-integer imap-max-line-length
     Maximum IMAP command line length.  Some clients generate very long command lines with huge mailboxes, so you may need to raise this if you get "Too long argument" or "IMAP command line too large" errors often. Defaults to 64000.

 -- dovecot-configuration parameter: string imap-logout-format
     IMAP logout format string:

     %i
          total number of bytes read from client

     %o
          total number of bytes sent to client.

     See doc/wiki/Variables.txt for a list of all the variables you can use. Defaults to "in=%i out=%o deleted=%{deleted} expunged=%{expunged} trashed=%{trashed} hdr_count=%{fetch_hdr_count} hdr_bytes=%{fetch_hdr_bytes} body_count=%{fetch_body_count} body_bytes=%{fetch_body_bytes}".

 -- dovecot-configuration parameter: string imap-capability
     Override the IMAP CAPABILITY response.  If the value begins with '+', add the given capabilities on top of the defaults (e.g. +XFOO XBAR). Defaults to "".

 -- dovecot-configuration parameter: string imap-idle-notify-interval
     How long to wait between "OK Still here" notifications when client is IDLEing. Defaults to "2 mins".

 -- dovecot-configuration parameter: string imap-id-send
     ID field names and values to send to clients.  Using * as the value makes Dovecot use the default value.  The following fields have default values currently: name, version, os, os-version, support-url, support-email. Defaults to "".

 -- dovecot-configuration parameter: string imap-id-log
     ID fields sent by client to log.  * means everything. Defaults to "".

 -- dovecot-configuration parameter: space-separated-string-list imap-client-workarounds
     Workarounds for various client bugs:

     delay-newmail
          Send EXISTS/RECENT new mail notifications only when replying to NOOP and CHECK commands.  Some clients ignore them otherwise, for example OSX Mail (<v2.1).  Outlook Express breaks more badly though, without this it may show user "Message no longer in server" errors.  Note that OE6 still breaks even with this workaround if synchronization is set to "Headers Only".

     tb-extra-mailbox-sep
          Thunderbird gets somehow confused with LAYOUT=fs (mbox and dbox) and adds extra / suffixes to mailbox names.  This option causes Dovecot to ignore the extra / instead of treating it as invalid mailbox name.

     tb-lsub-flags
          Show \Noselect flags for LSUB replies with LAYOUT=fs (e.g. mbox). This makes Thunderbird realize they aren't selectable and show them greyed out, instead of only later giving "not selectable" popup error.

     Defaults to '().

 -- dovecot-configuration parameter: string imap-urlauth-host
     Host allowed in URLAUTH URLs sent by client.  "*" allows all. Defaults to "".

Whew!  Lots of configuration options.  The nice thing about it though is that Guix has a complete interface to Dovecot's configuration language.  This allows not only a nice way to declare configurations, but also offers reflective capabilities as well: users can write code to inspect and transform configurations from within Scheme.

However, it could be that you just want to get a dovecot.conf up and running.  In that case, you can pass an opaque-dovecot-configuration as the #:config parameter to dovecot-service.  As its name indicates, an opaque configuration does not have easy reflective capabilities.

Available opaque-dovecot-configuration fields are:

 -- opaque-dovecot-configuration parameter: package dovecot
     The dovecot package.

 -- opaque-dovecot-configuration parameter: string string
     The contents of the dovecot.conf, as a string.

For example, if your dovecot.conf is just the empty string, you could instantiate a dovecot service like this:

     (dovecot-service #:config
                      (opaque-dovecot-configuration
                       (string "")))

OpenSMTPD Service
.................

 -- Variable: opensmtpd-service-type
     This is the type of the OpenSMTPD (https://www.opensmtpd.org) service, whose value should be an opensmtpd-configuration object as in this example:

          (service opensmtpd-service-type
                   (opensmtpd-configuration
                     (config-file (local-file "./my-smtpd.conf"))))

 -- Data Type: opensmtpd-configuration
     Data type representing the configuration of opensmtpd.

     package (default: OPENSMTPD)
          Package object of the OpenSMTPD SMTP server.

     shepherd-requirement (default: '())
          This option can be used to provide a list of symbols naming Shepherd services that this service will depend on, such as 'networking if you want to configure OpenSMTPD to listen on non-loopback interfaces.

     config-file (default: %default-opensmtpd-config-file)
          File-like object of the OpenSMTPD configuration file to use.  By default it listens on the loopback network interface, and allows for mail from users and daemons on the local machine, as well as permitting email to remote servers.  Run man smtpd.conf for more information.

     setgid-commands? (default: #t)
          Make the following commands setgid to smtpq so they can be executed: smtpctl, sendmail, send-mail, makemap, mailq, and newaliases. See Setuid Programs, for more information on setgid programs.

Exim Service
............

 -- Variable: exim-service-type
     This is the type of the Exim (https://exim.org) mail transfer agent (MTA), whose value should be an exim-configuration object as in this example:

          (service exim-service-type
                   (exim-configuration
                     (config-file (local-file "./my-exim.conf"))))

In order to use an exim-service-type service you must also have a mail-aliases-service-type service present in your operating-system (even if it has no aliases).

 -- Data Type: exim-configuration
     Data type representing the configuration of exim.

     package (default: EXIM)
          Package object of the Exim server.

     config-file (default: #f)
          File-like object of the Exim configuration file to use.  If its value is #f then use the default configuration file from the package provided in package.  The resulting configuration file is loaded after setting the exim_user and exim_group configuration variables.

Getmail service
...............

 -- Variable: getmail-service-type
     This is the type of the Getmail (http://pyropus.ca/software/getmail/) mail retriever, whose value should be a getmail-configuration.

Available getmail-configuration fields are:

 -- getmail-configuration parameter: symbol name
     A symbol to identify the getmail service.

     Defaults to "unset".

 -- getmail-configuration parameter: package package
     The getmail package to use.

 -- getmail-configuration parameter: string user
     The user to run getmail as.

     Defaults to "getmail".

 -- getmail-configuration parameter: string group
     The group to run getmail as.

     Defaults to "getmail".

 -- getmail-configuration parameter: string directory
     The getmail directory to use.

     Defaults to "/var/lib/getmail/default".

 -- getmail-configuration parameter: getmail-configuration-file rcfile
     The getmail configuration file to use.

     Available getmail-configuration-file fields are:

      -- getmail-configuration-file parameter: getmail-retriever-configuration retriever
          What mail account to retrieve mail from, and how to access that account.

          Available getmail-retriever-configuration fields are:

           -- getmail-retriever-configuration parameter: string type
               The type of mail retriever to use.  Valid values include passwd and static.

               Defaults to "SimpleIMAPSSLRetriever".

           -- getmail-retriever-configuration parameter: string server
               Username to login to the mail server with.

               Defaults to unset.

           -- getmail-retriever-configuration parameter: string username
               Username to login to the mail server with.

               Defaults to unset.

           -- getmail-retriever-configuration parameter: non-negative-integer port
               Port number to connect to.

               Defaults to #f.

           -- getmail-retriever-configuration parameter: string password
               Override fields from passwd.

               Defaults to "".

           -- getmail-retriever-configuration parameter: list password-command
               Override fields from passwd.

               Defaults to '().

           -- getmail-retriever-configuration parameter: string keyfile
               PEM-formatted key file to use for the TLS negotiation.

               Defaults to "".

           -- getmail-retriever-configuration parameter: string certfile
               PEM-formatted certificate file to use for the TLS negotiation.

               Defaults to "".

           -- getmail-retriever-configuration parameter: string ca-certs
               CA certificates to use.

               Defaults to "".

           -- getmail-retriever-configuration parameter: parameter-alist extra-parameters
               Extra retriever parameters.

               Defaults to '().

      -- getmail-configuration-file parameter: getmail-destination-configuration destination
          What to do with retrieved messages.

          Available getmail-destination-configuration fields are:

           -- getmail-destination-configuration parameter: string type
               The type of mail destination.  Valid values include Maildir, Mboxrd and MDA_external.

               Defaults to unset.

           -- getmail-destination-configuration parameter: string-or-filelike path
               The path option for the mail destination.  The behaviour depends on the chosen type.

               Defaults to "".

           -- getmail-destination-configuration parameter: parameter-alist extra-parameters
               Extra destination parameters

               Defaults to '().

      -- getmail-configuration-file parameter: getmail-options-configuration options
          Configure getmail.

          Available getmail-options-configuration fields are:

           -- getmail-options-configuration parameter: non-negative-integer verbose
               If set to 0, getmail will only print warnings and errors.  A value of 1 means that messages will be printed about retrieving and deleting messages.  If set to 2, getmail will print messages about each of its actions.

               Defaults to 1.

           -- getmail-options-configuration parameter: boolean read-all
               If true, getmail will retrieve all available messages.  Otherwise it will only retrieve messages it hasn't seen previously.

               Defaults to #t.

           -- getmail-options-configuration parameter: boolean delete
               If set to true, messages will be deleted from the server after retrieving and successfully delivering them.  Otherwise, messages will be left on the server.

               Defaults to #f.

           -- getmail-options-configuration parameter: non-negative-integer delete-after
               Getmail will delete messages this number of days after seeing them, if they have been delivered.  This means messages will be left on the server this number of days after delivering them.  A value of 0 disabled this feature.

               Defaults to 0.

           -- getmail-options-configuration parameter: non-negative-integer delete-bigger-than
               Delete messages larger than this of bytes after retrieving them, even if the delete and delete-after options are disabled.  A value of 0 disables this feature.

               Defaults to 0.

           -- getmail-options-configuration parameter: non-negative-integer max-bytes-per-session
               Retrieve messages totalling up to this number of bytes before closing the session with the server.  A value of 0 disables this feature.

               Defaults to 0.

           -- getmail-options-configuration parameter: non-negative-integer max-message-size
               Don't retrieve messages larger than this number of bytes.  A value of 0 disables this feature.

               Defaults to 0.

           -- getmail-options-configuration parameter: boolean delivered-to
               If true, getmail will add a Delivered-To header to messages.

               Defaults to #t.

           -- getmail-options-configuration parameter: boolean received
               If set, getmail adds a Received header to the messages.

               Defaults to #t.

           -- getmail-options-configuration parameter: string message-log
               Getmail will record a log of its actions to the named file.  A value of "" disables this feature.

               Defaults to "".

           -- getmail-options-configuration parameter: boolean message-log-syslog
               If true, getmail will record a log of its actions using the system logger.

               Defaults to #f.

           -- getmail-options-configuration parameter: boolean message-log-verbose
               If true, getmail will log information about messages not retrieved and the reason for not retrieving them, as well as starting and ending information lines.

               Defaults to #f.

           -- getmail-options-configuration parameter: parameter-alist extra-parameters
               Extra options to include.

               Defaults to '().

 -- getmail-configuration parameter: list idle
     A list of mailboxes that getmail should wait on the server for new mail notifications.  This depends on the server supporting the IDLE extension.

     Defaults to '().

 -- getmail-configuration parameter: list environment-variables
     Environment variables to set for getmail.

     Defaults to '().

Mail Aliases Service
....................

 -- Variable: mail-aliases-service-type
     This is the type of the service which provides /etc/aliases, specifying how to deliver mail to users on this system.

          (service mail-aliases-service-type
                   '(("postmaster" "bob")
                     ("bob" "bob@example.com" "bob@example2.com")))

The configuration for a mail-aliases-service-type service is an association list denoting how to deliver mail that comes to this system.  Each entry is of the form (alias addresses ...), with alias specifying the local alias and addresses specifying where to deliver this user's mail.

The aliases aren't required to exist as users on the local system.  In the above example, there doesn't need to be a postmaster entry in the operating-system's user-accounts in order to deliver the postmaster mail to bob (which subsequently would deliver mail to bob@example.com and bob@example2.com).

GNU Mailutils IMAP4 Daemon
..........................

 -- Variable: imap4d-service-type
     This is the type of the GNU Mailutils IMAP4 Daemon (see imap4d (GNU Mailutils Manual)), whose value should be an imap4d-configuration object as in this example:

          (service imap4d-service-type
                   (imap4d-configuration
                     (config-file (local-file "imap4d.conf"))))

 -- Data Type: imap4d-configuration
     Data type representing the configuration of imap4d.

     package (default: mailutils)
          The package that provides imap4d.

     config-file (default: %default-imap4d-config-file)
          File-like object of the configuration file to use, by default it will listen on TCP port 143 of localhost.  See Conf-imap4d (GNU Mailutils Manual), for details.

Radicale Service
................

 -- Variable: radicale-service-type
     This is the type of the Radicale (https://radicale.org) CalDAV/CardDAV server whose value should be a radicale-configuration.

 -- Data Type: radicale-configuration
     Data type representing the configuration of radicale.

     package (default: radicale)
          The package that provides radicale.

     config-file (default: %default-radicale-config-file)
          File-like object of the configuration file to use, by default it will listen on TCP port 5232 of localhost and use the htpasswd file at /var/lib/radicale/users with no (plain) encryption.

Rspamd Service
..............

 -- Variable: rspamd-service-type
     This is the type of the Rspamd (https://rspamd.com/) filtering system whose value should be a rspamd-configuration.

 -- Data Type: rspamd-configuration
     Available rspamd-configuration fields are:

     package (default: rspamd) (type: file-like)
          The package that provides rspamd.

     config-file (default: %default-rspamd-config-file) (type: file-like)
          File-like object of the configuration file to use.  By default all workers are enabled except fuzzy and they are binded to their usual ports, e.g localhost:11334, localhost:11333 and so on

     local.d-files (default: ()) (type: directory-tree)
          Configuration files in local.d, provided as a list of two element lists where the first element is the filename and the second one is a file-like object.  Settings in these files will be merged with the defaults.

     override.d-files (default: ()) (type: directory-tree)
          Configuration files in override.d, provided as a list of two element lists where the first element is the filename and the second one is a file-like object.  Settings in these files will override the defaults.

     user (default: %default-rspamd-account) (type: user-account)
          The user to run rspamd as.

     group (default: %default-rspamd-group) (type: user-group)
          The group to run rspamd as.

     debug? (default: #f) (type: boolean)
          Force debug output.

     insecure? (default: #f) (type: boolean)
          Ignore running workers as privileged users.

     skip-template? (default: #f) (type: boolean)
          Do not apply Jinja templates.

     shepherd-requirements (default: (loopback)) (type: list-of-symbols)
          This is a list of symbols naming Shepherd services that this service will depend on.

Messaging Services
------------------

The (gnu services messaging) module provides Guix service definitions for messaging services.  Currently it provides the following services:

Prosody Service
...............

 -- Variable: prosody-service-type
     This is the type for the Prosody XMPP communication server (https://prosody.im).  Its value must be a prosody-configuration record as in this example:

          (service prosody-service-type
                   (prosody-configuration
                    (modules-enabled (cons* "groups" "mam" %default-modules-enabled))
                    (int-components
                     (list
                      (int-component-configuration
                       (hostname "conference.example.net")
                       (plugin "muc")
                       (mod-muc (mod-muc-configuration)))))
                    (virtualhosts
                     (list
                      (virtualhost-configuration
                       (domain "example.net"))))))

     See below for details about prosody-configuration.

By default, Prosody does not need much configuration.  Only one virtualhosts field is needed: it specifies the domain you wish Prosody to serve.

You can perform various sanity checks on the generated configuration with the prosodyctl check command.

Prosodyctl will also help you to import certificates from the letsencrypt directory so that the prosody user can access them.  See https://prosody.im/doc/letsencrypt.

     prosodyctl --root cert import /etc/certs

The available configuration parameters follow.  Each parameter definition is preceded by its type; for example, string-list foo indicates that the foo parameter should be specified as a list of strings.  Types starting with maybe- denote parameters that won't show up in prosody.cfg.lua when their value is left unspecified.

There is also a way to specify the configuration as a string, if you have an old prosody.cfg.lua file that you want to port over from some other system; see the end for more details.

The file-object type designates either a file-like object (see file-like objects) or a file name.

Available prosody-configuration fields are:

 -- prosody-configuration parameter: package prosody
     The Prosody package.

 -- prosody-configuration parameter: file-name data-path
     Location of the Prosody data storage directory.  See https://prosody.im/doc/configure. Defaults to "/var/lib/prosody".

 -- prosody-configuration parameter: file-object-list plugin-paths
     Additional plugin directories.  They are searched in all the specified paths in order.  See https://prosody.im/doc/plugins_directory. Defaults to '().

 -- prosody-configuration parameter: file-name certificates
     Every virtual host and component needs a certificate so that clients and servers can securely verify its identity.  Prosody will automatically load certificates/keys from the directory specified here. Defaults to "/etc/prosody/certs".

 -- prosody-configuration parameter: string-list admins
     This is a list of accounts that are admins for the server.  Note that you must create the accounts separately.  See https://prosody.im/doc/admins and https://prosody.im/doc/creating_accounts. Example: (admins '("user1@example.com" "user2@example.net")) Defaults to '().

 -- prosody-configuration parameter: boolean use-libevent?
     Enable use of libevent for better performance under high load.  See https://prosody.im/doc/libevent. Defaults to #f.

 -- prosody-configuration parameter: module-list modules-enabled
     This is the list of modules Prosody will load on startup.  It looks for mod_modulename.lua in the plugins folder, so make sure that exists too. Documentation on modules can be found at: https://prosody.im/doc/modules. Defaults to '("roster" "saslauth" "tls" "dialback" "disco" "carbons" "private" "blocklist" "vcard" "version" "uptime" "time" "ping" "pep" "register" "admin_adhoc").

 -- prosody-configuration parameter: string-list modules-disabled
     "offline", "c2s" and "s2s" are auto-loaded, but should you want to disable them then add them to this list. Defaults to '().

 -- prosody-configuration parameter: file-object groups-file
     Path to a text file where the shared groups are defined.  If this path is empty then mod_groups does nothing.  See https://prosody.im/doc/modules/mod_groups. Defaults to "/var/lib/prosody/sharedgroups.txt".

 -- prosody-configuration parameter: boolean allow-registration?
     Disable account creation by default, for security.  See https://prosody.im/doc/creating_accounts. Defaults to #f.

 -- prosody-configuration parameter: maybe-ssl-configuration ssl
     These are the SSL/TLS-related settings.  Most of them are disabled so to use Prosody's defaults.  If you do not completely understand these options, do not add them to your config, it is easy to lower the security of your server using them.  See https://prosody.im/doc/advanced_ssl_config.

     Available ssl-configuration fields are:

      -- ssl-configuration parameter: maybe-string protocol
          This determines what handshake to use.

      -- ssl-configuration parameter: maybe-file-name key
          Path to your private key file.

      -- ssl-configuration parameter: maybe-file-name certificate
          Path to your certificate file.

      -- ssl-configuration parameter: file-object capath
          Path to directory containing root certificates that you wish Prosody to trust when verifying the certificates of remote servers. Defaults to "/etc/ssl/certs".

      -- ssl-configuration parameter: maybe-file-object cafile
          Path to a file containing root certificates that you wish Prosody to trust. Similar to capath but with all certificates concatenated together.

      -- ssl-configuration parameter: maybe-string-list verify
          A list of verification options (these mostly map to OpenSSL's set_verify() flags).

      -- ssl-configuration parameter: maybe-string-list options
          A list of general options relating to SSL/TLS.  These map to OpenSSL's set_options().  For a full list of options available in LuaSec, see the LuaSec source.

      -- ssl-configuration parameter: maybe-non-negative-integer depth
          How long a chain of certificate authorities to check when looking for a trusted root certificate.

      -- ssl-configuration parameter: maybe-string ciphers
          An OpenSSL cipher string.  This selects what ciphers Prosody will offer to clients, and in what order.

      -- ssl-configuration parameter: maybe-file-name dhparam
          A path to a file containing parameters for Diffie-Hellman key exchange.  You can create such a file with: openssl dhparam -out /etc/prosody/certs/dh-2048.pem 2048

      -- ssl-configuration parameter: maybe-string curve
          Curve for Elliptic curve Diffie-Hellman.  Prosody's default is "secp384r1".

      -- ssl-configuration parameter: maybe-string-list verifyext
          A list of ``extra'' verification options.

      -- ssl-configuration parameter: maybe-string password
          Password for encrypted private keys.

 -- prosody-configuration parameter: boolean c2s-require-encryption?
     Whether to force all client-to-server connections to be encrypted or not. See https://prosody.im/doc/modules/mod_tls. Defaults to #f.

 -- prosody-configuration parameter: string-list disable-sasl-mechanisms
     Set of mechanisms that will never be offered.  See https://prosody.im/doc/modules/mod_saslauth. Defaults to '("DIGEST-MD5").

 -- prosody-configuration parameter: boolean s2s-require-encryption?
     Whether to force all server-to-server connections to be encrypted or not. See https://prosody.im/doc/modules/mod_tls. Defaults to #f.

 -- prosody-configuration parameter: boolean s2s-secure-auth?
     Whether to require encryption and certificate authentication.  This provides ideal security, but requires servers you communicate with to support encryption AND present valid, trusted certificates.  See https://prosody.im/doc/s2s#security. Defaults to #f.

 -- prosody-configuration parameter: string-list s2s-insecure-domains
     Many servers don't support encryption or have invalid or self-signed certificates.  You can list domains here that will not be required to authenticate using certificates.  They will be authenticated using DNS.  See https://prosody.im/doc/s2s#security. Defaults to '().

 -- prosody-configuration parameter: string-list s2s-secure-domains
     Even if you leave s2s-secure-auth? disabled, you can still require valid certificates for some domains by specifying a list here.  See https://prosody.im/doc/s2s#security. Defaults to '().

 -- prosody-configuration parameter: string authentication
     Select the authentication backend to use.  The default provider stores passwords in plaintext and uses Prosody's configured data storage to store the authentication data.  If you do not trust your server please see https://prosody.im/doc/modules/mod_auth_internal_hashed for information about using the hashed backend.  See also https://prosody.im/doc/authentication Defaults to "internal_plain".

 -- prosody-configuration parameter: maybe-string log
     Set logging options.  Advanced logging configuration is not yet supported by the Prosody service.  See https://prosody.im/doc/logging. Defaults to "*syslog".

 -- prosody-configuration parameter: file-name pidfile
     File to write pid in.  See https://prosody.im/doc/modules/mod_posix. Defaults to "/var/run/prosody/prosody.pid".

 -- prosody-configuration parameter: maybe-non-negative-integer http-max-content-size
     Maximum allowed size of the HTTP body (in bytes).

 -- prosody-configuration parameter: maybe-string http-external-url
     Some modules expose their own URL in various ways.  This URL is built from the protocol, host and port used.  If Prosody sits behind a proxy, the public URL will be http-external-url instead.  See https://prosody.im/doc/http#external_url.

 -- prosody-configuration parameter: virtualhost-configuration-list virtualhosts
     A host in Prosody is a domain on which user accounts can be created.  For example if you want your users to have addresses like "john.smith@example.com" then you need to add a host "example.com".  All options in this list will apply only to this host.

          The name virtual host is used in configuration to avoid confusion with the actual physical host that Prosody is installed on.  A single Prosody instance can serve many domains, each one defined as a VirtualHost entry in Prosody's configuration.  Conversely a server that hosts a single domain would have just one VirtualHost entry.

          See https://prosody.im/doc/configure#virtual_host_settings.

     Available virtualhost-configuration fields are:

     all these prosody-configuration fields: admins, use-libevent?, modules-enabled, modules-disabled, groups-file, allow-registration?, ssl, c2s-require-encryption?, disable-sasl-mechanisms, s2s-require-encryption?, s2s-secure-auth?, s2s-insecure-domains, s2s-secure-domains, authentication, log, http-max-content-size, http-external-url, raw-content, plus:
      -- virtualhost-configuration parameter: string domain
          Domain you wish Prosody to serve.

 -- prosody-configuration parameter: int-component-configuration-list int-components
     Components are extra services on a server which are available to clients, usually on a subdomain of the main server (such as "mycomponent.example.com").  Example components might be chatroom servers, user directories, or gateways to other protocols.

     Internal components are implemented with Prosody-specific plugins.  To add an internal component, you simply fill the hostname field, and the plugin you wish to use for the component.

     See https://prosody.im/doc/components. Defaults to '().

     Available int-component-configuration fields are:

     all these prosody-configuration fields: admins, use-libevent?, modules-enabled, modules-disabled, groups-file, allow-registration?, ssl, c2s-require-encryption?, disable-sasl-mechanisms, s2s-require-encryption?, s2s-secure-auth?, s2s-insecure-domains, s2s-secure-domains, authentication, log, http-max-content-size, http-external-url, raw-content, plus:
      -- int-component-configuration parameter: string hostname
          Hostname of the component.

      -- int-component-configuration parameter: string plugin
          Plugin you wish to use for the component.

      -- int-component-configuration parameter: maybe-mod-muc-configuration mod-muc
          Multi-user chat (MUC) is Prosody's module for allowing you to create hosted chatrooms/conferences for XMPP users.

          General information on setting up and using multi-user chatrooms can be found in the ``Chatrooms'' documentation (https://prosody.im/doc/chatrooms), which you should read if you are new to XMPP chatrooms.

          See also https://prosody.im/doc/modules/mod_muc.

          Available mod-muc-configuration fields are:

           -- mod-muc-configuration parameter: string name
               The name to return in service discovery responses. Defaults to "Prosody Chatrooms".

           -- mod-muc-configuration parameter: string-or-boolean restrict-room-creation
               If #t, this will only allow admins to create new chatrooms. Otherwise anyone can create a room.  The value "local" restricts room creation to users on the service's parent domain.  E.g. user@example.com can create rooms on rooms.example.com.  The value "admin" restricts to service administrators only. Defaults to #f.

           -- mod-muc-configuration parameter: non-negative-integer max-history-messages
               Maximum number of history messages that will be sent to the member that has just joined the room. Defaults to 20.

 -- prosody-configuration parameter: ext-component-configuration-list ext-components
     External components use XEP-0114, which most standalone components support.  To add an external component, you simply fill the hostname field.  See https://prosody.im/doc/components. Defaults to '().

     Available ext-component-configuration fields are:

     all these prosody-configuration fields: admins, use-libevent?, modules-enabled, modules-disabled, groups-file, allow-registration?, ssl, c2s-require-encryption?, disable-sasl-mechanisms, s2s-require-encryption?, s2s-secure-auth?, s2s-insecure-domains, s2s-secure-domains, authentication, log, http-max-content-size, http-external-url, raw-content, plus:
      -- ext-component-configuration parameter: string component-secret
          Password which the component will use to log in.

      -- ext-component-configuration parameter: string hostname
          Hostname of the component.

 -- prosody-configuration parameter: non-negative-integer-list component-ports
     Port(s) Prosody listens on for component connections. Defaults to '(5347).

 -- prosody-configuration parameter: string component-interface
     Interface Prosody listens on for component connections. Defaults to "127.0.0.1".

 -- prosody-configuration parameter: maybe-raw-content raw-content
     Raw content that will be added to the configuration file.

It could be that you just want to get a prosody.cfg.lua up and running.  In that case, you can pass an opaque-prosody-configuration record as the value of prosody-service-type.  As its name indicates, an opaque configuration does not have easy reflective capabilities. Available opaque-prosody-configuration fields are:

 -- opaque-prosody-configuration parameter: package prosody
     The prosody package.

 -- opaque-prosody-configuration parameter: string prosody.cfg.lua
     The contents of the prosody.cfg.lua to use.

For example, if your prosody.cfg.lua is just the empty string, you could instantiate a prosody service like this:

     (service prosody-service-type
              (opaque-prosody-configuration
               (prosody.cfg.lua "")))

BitlBee Service
...............

BitlBee (https://bitlbee.org) is a gateway that provides an IRC interface to a variety of messaging protocols such as XMPP.

 -- Variable: bitlbee-service-type
     This is the service type for the BitlBee (https://bitlbee.org) IRC gateway daemon.  Its value is a bitlbee-configuration (see below).

     To have BitlBee listen on port 6667 on localhost, add this line to your services:

          (service bitlbee-service-type)

 -- Data Type: bitlbee-configuration
     This is the configuration for BitlBee, with the following fields:

     interface (default: "127.0.0.1")
     port (default: 6667)
          Listen on the network interface corresponding to the IP address specified in INTERFACE, on PORT.

          When INTERFACE is 127.0.0.1, only local clients can connect; when it is 0.0.0.0, connections can come from any networking interface.

     bitlbee (default: bitlbee)
          The BitlBee package to use.

     plugins (default: '())
          List of plugin packages to use---e.g., bitlbee-discord.

     extra-settings (default: "")
          Configuration snippet added as-is to the BitlBee configuration file.

Quassel Service
...............

Quassel (https://quassel-irc.org/) is a distributed IRC client, meaning that one or more clients can attach to and detach from the central core.

 -- Variable: quassel-service-type
     This is the service type for the Quassel (https://quassel-irc.org/) IRC backend daemon.  Its value is a quassel-configuration (see below).

 -- Data Type: quassel-configuration
     This is the configuration for Quassel, with the following fields:

     quassel (default: quassel)
          The Quassel package to use.

     interface (default: "::,0.0.0.0")

     port (default: 4242)
          Listen on the network interface(s) corresponding to the IPv4 or IPv6 interfaces specified in the comma delimited INTERFACE, on PORT.

     loglevel (default: "Info")
          The level of logging desired.  Accepted values are Debug, Info, Warning and Error.

Telephony Services
------------------

The (gnu services telephony) module contains Guix service definitions for telephony services.  Currently it provides the following services:

Jami
....

 -- Variable: jami-service-type
     The service type for running Jami as a service.  It takes a jami-configuration object as a value, documented below.  This section describes how to configure a Jami server that can be used to host video (or audio) conferences, among other uses.  The following example demonstrates how to specify Jami account archives (backups) to be provisioned automatically:

          (service jami-service-type
                   (jami-configuration
                    (accounts
                     (list (jami-account
                            (archive "/etc/jami/unencrypted-account-1.gz"))
                           (jami-account
                            (archive "/etc/jami/unencrypted-account-2.gz"))))))

     When the accounts field is specified, the Jami account files of the service found under /var/lib/jami are recreated every time the service starts.

     Jami accounts and their corresponding backup archives can be generated using the jami or jami-gnome Jami clients.  The accounts should not be password-protected, but it is wise to ensure their files are only readable by root.

     The next example shows how to declare that only some contacts should be allowed to communicate with a given account:

          (service jami-service-type
                   (jami-configuration
                    (accounts
                     (list (jami-account
                            (archive "/etc/jami/unencrypted-account-1.gz")
                            (peer-discovery? #t)
                            (rendezvous-point? #t)
                            (allowed-contacts
                             '("1dbcb0f5f37324228235564b79f2b9737e9a008f"
                               "2dbcb0f5f37324228235564b79f2b9737e9a008f")))))))

     In this mode, only the declared allowed-contacts can initiate communication with the Jami account.  This can be used, for example, with rendezvous point accounts to create a private video conferencing space.

     To put the system administrator in full control of the conferences hosted on their system, the Jami service supports the following actions:

          # herd doc jami list-actions
          (list-accounts
           list-account-details
           list-banned-contacts
           list-contacts
           list-moderators
           add-moderator
           ban-contact
           enable-account
           disable-account)

     The above actions aim to provide the most valuable actions for moderation purposes, not to cover the whole Jami API.  Users wanting to interact with the Jami daemon from Guile may be interested in experimenting with the (gnu build jami-service) module, which powers the above Shepherd actions.

     The add-moderator and ban-contact actions accept a contact fingerprint (40 characters long hash) as first argument and an account fingerprint or username as second argument:

          # herd add-moderator jami 1dbcb0f5f37324228235564b79f2b9737e9a008f \
            f3345f2775ddfe07a4b0d95daea111d15fbc1199

          # herd list-moderators jami
          Moderators for account f3345f2775ddfe07a4b0d95daea111d15fbc1199:
            - 1dbcb0f5f37324228235564b79f2b9737e9a008f

     In the case of ban-contact, the second username argument is optional; when omitted, the account is banned from all Jami accounts:

          # herd ban-contact jami 1dbcb0f5f37324228235564b79f2b9737e9a008f

          # herd list-banned-contacts jami
          Banned contacts for account f3345f2775ddfe07a4b0d95daea111d15fbc1199:
            - 1dbcb0f5f37324228235564b79f2b9737e9a008f

     Banned contacts are also stripped from their moderation privileges.

     The disable-account action allows to completely disconnect an account from the network, making it unreachable, while enable-account does the inverse.  They accept a single account username or fingerprint as first argument:

          # herd disable-account jami f3345f2775ddfe07a4b0d95daea111d15fbc1199

          # herd list-accounts jami
          The following Jami accounts are available:
            - f3345f2775ddfe07a4b0d95daea111d15fbc1199 (dummy) [disabled]

     The list-account-details action prints the detailed parameters of each accounts in the Recutils format, which means the recsel command can be used to select accounts of interest (see Selection Expressions (GNU recutils manual)).  Note that period characters (.) found in the account parameter keys are mapped to underscores (_) in the output, to meet the requirements of the Recutils format.  The following example shows how to print the account fingerprints for all accounts operating in the rendezvous point mode:

          # herd list-account-details jami | \
            recsel -p Account.username -e 'Account.rendezVous ~ "true"'
          Account_username: f3345f2775ddfe07a4b0d95daea111d15fbc1199

     The remaining actions should be self-explanatory.

     The complete set of available configuration options is detailed below.

 -- Data Type: jami-configuration
     Available jami-configuration fields are:

     libjami (default: libjami) (type: package)
          The Jami daemon package to use.

     dbus (default: dbus-for-jami) (type: package)
          The D-Bus package to use to start the required D-Bus session.

     nss-certs (default: nss-certs) (type: package)
          The nss-certs package to use to provide TLS certificates.

     enable-logging? (default: #t) (type: boolean)
          Whether to enable logging to syslog.

     debug? (default: #f) (type: boolean)
          Whether to enable debug level messages.

     auto-answer? (default: #f) (type: boolean)
          Whether to force automatic answer to incoming calls.

     accounts (type: maybe-jami-account-list)
          A list of Jami accounts to be (re-)provisioned every time the Jami daemon service starts.  When providing this field, the account directories under /var/lib/jami/ are recreated every time the service starts, ensuring a consistent state.

 -- Data Type: jami-account
     Available jami-account fields are:

     archive (type: string-or-computed-file)
          The account archive (backup) file name of the account.  This is used to provision the account when the service starts.  The account archive should not be encrypted.  It is highly recommended to make it readable only to the root user (i.e., not in the store), to guard against leaking the secret key material of the Jami account it contains.

     allowed-contacts (type: maybe-account-fingerprint-list)
          The list of allowed contacts for the account, entered as their 40 characters long fingerprint.  Messages or calls from accounts not in that list will be rejected.  When left specified, the configuration of the account archive is used as-is with respect to contacts and public inbound calls/messaging allowance, which typically defaults to allow any contact to communicate with the account.

     moderators (type: maybe-account-fingerprint-list)
          The list of contacts that should have moderation privileges (to ban, mute, etc.  other users) in rendezvous conferences, entered as their 40 characters long fingerprint.  When left unspecified, the configuration of the account archive is used as-is with respect to moderation, which typically defaults to allow anyone to moderate.

     rendezvous-point? (type: maybe-boolean)
          Whether the account should operate in the rendezvous mode.  In this mode, all the incoming audio/video calls are mixed into a conference. When left unspecified, the value from the account archive prevails.

     peer-discovery? (type: maybe-boolean)
          Whether peer discovery should be enabled.  Peer discovery is used to discover other OpenDHT nodes on the local network, which can be useful to maintain communication between devices on such network even when the connection to the Internet has been lost.  When left unspecified, the value from the account archive prevails.

     bootstrap-hostnames (type: maybe-list-of-strings)
          A list of hostnames or IPs pointing to OpenDHT nodes, that should be used to initially join the OpenDHT network.  When left unspecified, the value from the account archive prevails.

     name-server-uri (type: maybe-string)
          The URI of the name server to use, that can be used to retrieve the account fingerprint for a registered username.

Mumble server
.............

This section describes how to set up and run a Mumble (https://mumble.info) server (formerly known as Murmur).

 -- Variable: mumble-server-service-type

     This is the service to run a Mumble server.  It takes a mumble-server-configuration object as its value, defined below.

 -- Data Type: mumble-server-configuration
     The service type for the Mumble server.  An example configuration can look like this:

          (service mumble-server-service-type
                   (mumble-server-configuration
                    (welcome-text
                      "Welcome to this Mumble server running on Guix!")
                    (cert-required? #t) ;disallow text password logins
                    (ssl-cert "/etc/certs/mumble.example.com/fullchain.pem")
                    (ssl-key "/etc/certs/mumble.example.com/privkey.pem")))

     After reconfiguring your system, you can manually set the mumble-server SuperUser password with the command that is printed during the activation phase.

     It is recommended to register a normal Mumble user account and grant it admin or moderator rights. You can use the mumble client to login as new normal user, register yourself, and log out. For the next step login with the name SuperUser use the SuperUser password that you set previously, and grant your newly registered mumble user administrator or moderator rights and create some channels.

     Available mumble-server-configuration fields are:

     package (default: mumble)
          Package that contains bin/mumble-server.

     user (default: "mumble-server")
          User who will run the Mumble-Server server.

     group (default: "mumble-server")
          Group of the user who will run the mumble-server server.

     port (default: 64738)
          Port on which the server will listen.

     welcome-text (default: "")
          Welcome text sent to clients when they connect.

     server-password (default: "")
          Password the clients have to enter in order to connect.

     max-users (default: 100)
          Maximum of users that can be connected to the server at once.

     max-user-bandwidth (default: #f)
          Maximum voice traffic a user can send per second.

     database-file (default: "/var/lib/mumble-server/db.sqlite")
          File name of the sqlite database. The service's user will become the owner of the directory.

     log-file (default: "/var/log/mumble-server/mumble-server.log")
          File name of the log file. The service's user will become the owner of the directory.

     autoban-attempts (default: 10)
          Maximum number of logins a user can make in autoban-timeframe without getting auto banned for autoban-time.

     autoban-timeframe (default: 120)
          Timeframe for autoban in seconds.

     autoban-time (default: 300)
          Amount of time in seconds for which a client gets banned when violating the autoban limits.

     opus-threshold (default: 100)
          Percentage of clients that need to support opus before switching over to opus audio codec.

     channel-nesting-limit (default: 10)
          How deep channels can be nested at maximum.

     channelname-regex (default: #f)
          A string in form of a Qt regular expression that channel names must conform to.

     username-regex (default: #f)
          A string in form of a Qt regular expression that user names must conform to.

     text-message-length (default: 5000)
          Maximum size in bytes that a user can send in one text chat message.

     image-message-length (default: (* 128 1024))
          Maximum size in bytes that a user can send in one image message.

     cert-required? (default: #f)
          If it is set to #t clients that use weak password authentication will not be accepted.  Users must have completed the certificate wizard to join.

     remember-channel? (default: #f)
          Should mumble-server remember the last channel each user was in when they disconnected and put them into the remembered channel when they rejoin.

     allow-html? (default: #f)
          Should html be allowed in text messages, user comments, and channel descriptions.

     allow-ping? (default: #f)
          Setting to true exposes the current user count, the maximum user count, and the server's maximum bandwidth per client to unauthenticated users.  In the Mumble client, this information is shown in the Connect dialog.

          Disabling this setting will prevent public listing of the server.

     bonjour? (default: #f)
          Should the server advertise itself in the local network through the bonjour protocol.

     send-version? (default: #f)
          Should the mumble-server server version be exposed in ping requests.

     log-days (default: 31)
          Mumble also stores logs in the database, which are accessible via RPC. The default is 31 days of months, but you can set this setting to 0 to keep logs forever, or -1 to disable logging to the database.

     obfuscate-ips? (default: #t)
          Should logged ips be obfuscated to protect the privacy of users.

     ssl-cert (default: #f)
          File name of the SSL/TLS certificate used for encrypted connections.

               (ssl-cert "/etc/certs/example.com/fullchain.pem")

     ssl-key (default: #f)
          Filepath to the ssl private key used for encrypted connections.

               (ssl-key "/etc/certs/example.com/privkey.pem")

     ssl-dh-params (default: #f)
          File name of a PEM-encoded file with Diffie-Hellman parameters for the SSL/TLS encryption.  Alternatively you set it to "@ffdhe2048", "@ffdhe3072", "@ffdhe4096", "@ffdhe6144" or "@ffdhe8192" to use bundled parameters from RFC 7919.

     ssl-ciphers (default: #f)
          The ssl-ciphers option chooses the cipher suites to make available for use in SSL/TLS.

          This option is specified using OpenSSL cipher list notation (https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT).

          It is recommended that you try your cipher string using 'openssl ciphers <string>' before setting it here, to get a feel for which cipher suites you will get. After setting this option, it is recommend that you inspect your Mumble server log to ensure that Mumble is using the cipher suites that you expected it to.

               Changing this option may impact the backwards compatibility of your Mumble-Server server, and can remove the ability for older Mumble clients to be able to connect to it.

     public-registration (default: #f)
          Must be a <mumble-server-public-registration-configuration> record or #f.

          You can optionally register your server in the public server list that the mumble client shows on startup. You cannot register your server if you have set a server-password, or set allow-ping to #f.

          It might take a few hours until it shows up in the public list.

     file (default: #f)
          Optional alternative override for this configuration.

 -- Data Type: mumble-server-public-registration-configuration
     Configuration for public registration of a mumble-server service.

     name
          This is a display name for your server.  Not to be confused with the hostname.

     password
          A password to identify your registration. Subsequent updates will need the same password.  Don't lose your password.

     url
          This should be a http:// or https:// link to your web site.

     hostname (default: #f)
          By default your server will be listed by its IP address. If it is set your server will be linked by this host name instead.

     Due to historical reasons, all of the above mumble-server- procedures are also exported with the murmur- prefix. It is recommended that you switch to using mumble-server- going forward.

File-Sharing Services
---------------------

The (gnu services file-sharing) module provides services that assist with transferring files over peer-to-peer file-sharing networks.

Transmission Daemon Service
...........................

Transmission (https://transmissionbt.com/) is a flexible BitTorrent client that offers a variety of graphical and command-line interfaces.  A transmission-daemon-service-type service provides Transmission's headless variant, transmission-daemon, as a system service, allowing users to share files via BitTorrent even when they are not logged in.

 -- Variable: transmission-daemon-service-type
     The service type for the Transmission Daemon BitTorrent client. Its value must be a transmission-daemon-configuration object as in this example:

          (service transmission-daemon-service-type
                   (transmission-daemon-configuration
                    ;; Restrict access to the RPC ("control") interface
                    (rpc-authentication-required? #t)
                    (rpc-username "transmission")
                    (rpc-password
                     (transmission-password-hash
                      "transmission" ; desired password
                      "uKd1uMs9"))   ; arbitrary salt value

                    ;; Accept requests from this and other hosts on the
                    ;; local network
                    (rpc-whitelist-enabled? #t)
                    (rpc-whitelist '("::1" "127.0.0.1" "192.168.0.*"))

                    ;; Limit bandwidth use during work hours
                    (alt-speed-down (* 1024 2)) ;   2 MB/s
                    (alt-speed-up 512)          ; 512 kB/s

                    (alt-speed-time-enabled? #t)
                    (alt-speed-time-day 'weekdays)
                    (alt-speed-time-begin
                     (+ (* 60 8) 30))           ; 8:30 am
                    (alt-speed-time-end
                     (+ (* 60 (+ 12 5)) 30))))  ; 5:30 pm

Once the service is started, users can interact with the daemon through its Web interface (at http://localhost:9091/) or by using the transmission-remote command-line tool, available in the transmission package.  (Emacs users may want to also consider the emacs-transmission package.)  Both communicate with the daemon through its remote procedure call (RPC) interface, which by default is available to all users on the system; you may wish to change this by assigning values to the rpc-authentication-required?, rpc-username and rpc-password settings, as shown in the example above and documented further below.

The value for rpc-password must be a password hash of the type generated and used by Transmission clients.  This can be copied verbatim from an existing settings.json file, if another Transmission client is already being used.  Otherwise, the transmission-password-hash and transmission-random-salt procedures provided by this module can be used to obtain a suitable hash value.

 -- Procedure: transmission-password-hash password salt
     Returns a string containing the result of hashing PASSWORD together with SALT, in the format recognized by Transmission clients for their rpc-password configuration setting.

     SALT must be an eight-character string.  The transmission-random-salt procedure can be used to generate a suitable salt value at random.

 -- Procedure: transmission-random-salt
     Returns a string containing a random, eight-character salt value of the type generated and used by Transmission clients, suitable for passing to the transmission-password-hash procedure.

These procedures are accessible from within a Guile REPL started with the guix repl command (see Invoking guix repl).  This is useful for obtaining a random salt value to provide as the second parameter to `transmission-password-hash`, as in this example session:

     $ guix repl
     scheme@(guix-user)> ,use (gnu services file-sharing)
     scheme@(guix-user)> (transmission-random-salt)
     $1 = "uKd1uMs9"

Alternatively, a complete password hash can generated in a single step:

     scheme@(guix-user)> (transmission-password-hash "transmission"
     (transmission-random-salt))
     $2 = "{c8bbc6d1740cd8dc819a6e25563b67812c1c19c9VtFPfdsX"

The resulting string can be used as-is for the value of rpc-password, allowing the password to be kept hidden even in the operating-system configuration.

Torrent files downloaded by the daemon are directly accessible only to users in the ``transmission'' user group, who receive read-only access to the directory specified by the download-dir configuration setting (and also the directory specified by incomplete-dir, if incomplete-dir-enabled? is #t).  Downloaded files can be moved to another directory or deleted altogether using transmission-remote with its --move and --remove-and-delete options.

If the watch-dir-enabled? setting is set to #t, users in the ``transmission'' group are able also to place .torrent files in the directory specified by watch-dir to have the corresponding torrents added by the daemon.  (The trash-original-torrent-files? setting controls whether the daemon deletes these files after processing them.)

Some of the daemon's configuration settings can be changed temporarily by transmission-remote and similar tools. To undo these changes, use the service's reload action to have the daemon reload its settings from disk:

     # herd reload transmission-daemon

The full set of available configuration settings is defined by the transmission-daemon-configuration data type.

 -- Data Type: transmission-daemon-configuration
     The data type representing configuration settings for Transmission Daemon.  These correspond directly to the settings recognized by Transmission clients in their settings.json file.

Available transmission-daemon-configuration fields are:

 -- transmission-daemon-configuration parameter: package transmission
     The Transmission package to use.

 -- transmission-daemon-configuration parameter: non-negative-integer stop-wait-period
     The period, in seconds, to wait when stopping the service for transmission-daemon to exit before killing its process.  This allows the daemon time to complete its housekeeping and send a final update to trackers as it shuts down.  On slow hosts, or hosts with a slow network connection, this value may need to be increased.

     Defaults to 10.

 -- transmission-daemon-configuration parameter: string download-dir
     The directory to which torrent files are downloaded.

     Defaults to "/var/lib/transmission-daemon/downloads".

 -- transmission-daemon-configuration parameter: boolean incomplete-dir-enabled?
     If #t, files will be held in incomplete-dir while their torrent is being downloaded, then moved to download-dir once the torrent is complete.  Otherwise, files for all torrents (including those still being downloaded) will be placed in download-dir.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: maybe-string incomplete-dir
     The directory in which files from incompletely downloaded torrents will be held when incomplete-dir-enabled? is #t.

     Defaults to disabled.

 -- transmission-daemon-configuration parameter: umask umask
     The file mode creation mask used for downloaded files.  (See the umask man page for more information.)

     Defaults to 18.

 -- transmission-daemon-configuration parameter: boolean rename-partial-files?
     When #t, ``.part'' is appended to the name of partially downloaded files.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: preallocation-mode preallocation
     The mode by which space should be preallocated for downloaded files, one of none, fast (or sparse) and full. Specifying full will minimize disk fragmentation at a cost to file-creation speed.

     Defaults to fast.

 -- transmission-daemon-configuration parameter: boolean watch-dir-enabled?
     If #t, the directory specified by watch-dir will be watched for new .torrent files and the torrents they describe added automatically (and the original files removed, if trash-original-torrent-files? is #t).

     Defaults to #f.

 -- transmission-daemon-configuration parameter: maybe-string watch-dir
     The directory to be watched for .torrent files indicating new torrents to be added, when watch-dir-enabled is #t.

     Defaults to disabled.

 -- transmission-daemon-configuration parameter: boolean trash-original-torrent-files?
     When #t, .torrent files will be deleted from the watch directory once their torrent has been added (see watch-directory-enabled?).

     Defaults to #f.

 -- transmission-daemon-configuration parameter: boolean speed-limit-down-enabled?
     When #t, the daemon's download speed will be limited to the rate specified by speed-limit-down.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: non-negative-integer speed-limit-down
     The default global-maximum download speed, in kilobytes per second.

     Defaults to 100.

 -- transmission-daemon-configuration parameter: boolean speed-limit-up-enabled?
     When #t, the daemon's upload speed will be limited to the rate specified by speed-limit-up.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: non-negative-integer speed-limit-up
     The default global-maximum upload speed, in kilobytes per second.

     Defaults to 100.

 -- transmission-daemon-configuration parameter: boolean alt-speed-enabled?
     When #t, the alternate speed limits alt-speed-down and alt-speed-up are used (in place of speed-limit-down and speed-limit-up, if they are enabled) to constrain the daemon's bandwidth usage.  This can be scheduled to occur automatically at certain times during the week; see alt-speed-time-enabled?.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: non-negative-integer alt-speed-down
     The alternate global-maximum download speed, in kilobytes per second.

     Defaults to 50.

 -- transmission-daemon-configuration parameter: non-negative-integer alt-speed-up
     The alternate global-maximum upload speed, in kilobytes per second.

     Defaults to 50.

 -- transmission-daemon-configuration parameter: boolean alt-speed-time-enabled?
     When #t, the alternate speed limits alt-speed-down and alt-speed-up will be enabled automatically during the periods specified by alt-speed-time-day, alt-speed-time-begin and alt-time-speed-end.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: day-list alt-speed-time-day
     The days of the week on which the alternate-speed schedule should be used, specified either as a list of days (sunday, monday, and so on) or using one of the symbols weekdays, weekends or all.

     Defaults to all.

 -- transmission-daemon-configuration parameter: non-negative-integer alt-speed-time-begin
     The time of day at which to enable the alternate speed limits, expressed as a number of minutes since midnight.

     Defaults to 540.

 -- transmission-daemon-configuration parameter: non-negative-integer alt-speed-time-end
     The time of day at which to disable the alternate speed limits, expressed as a number of minutes since midnight.

     Defaults to 1020.

 -- transmission-daemon-configuration parameter: string bind-address-ipv4
     The IP address at which to listen for peer connections, or ``0.0.0.0'' to listen at all available IP addresses.

     Defaults to "0.0.0.0".

 -- transmission-daemon-configuration parameter: string bind-address-ipv6
     The IPv6 address at which to listen for peer connections, or ``::'' to listen at all available IPv6 addresses.

     Defaults to "::".

 -- transmission-daemon-configuration parameter: boolean peer-port-random-on-start?
     If #t, when the daemon starts it will select a port at random on which to listen for peer connections, from the range specified (inclusively) by peer-port-random-low and peer-port-random-high.  Otherwise, it listens on the port specified by peer-port.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: port-number peer-port-random-low
     The lowest selectable port number when peer-port-random-on-start? is #t.

     Defaults to 49152.

 -- transmission-daemon-configuration parameter: port-number peer-port-random-high
     The highest selectable port number when peer-port-random-on-start is #t.

     Defaults to 65535.

 -- transmission-daemon-configuration parameter: port-number peer-port
     The port on which to listen for peer connections when peer-port-random-on-start? is #f.

     Defaults to 51413.

 -- transmission-daemon-configuration parameter: boolean port-forwarding-enabled?
     If #t, the daemon will attempt to configure port-forwarding on an upstream gateway automatically using UPnP and NAT-PMP.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: encryption-mode encryption
     The encryption preference for peer connections, one of prefer-unencrypted-connections, prefer-encrypted-connections or require-encrypted-connections.

     Defaults to prefer-encrypted-connections.

 -- transmission-daemon-configuration parameter: maybe-string peer-congestion-algorithm
     The TCP congestion-control algorithm to use for peer connections, specified using a string recognized by the operating system in calls to setsockopt.  When left unspecified, the operating-system default is used.

     Note that on GNU/Linux systems, the kernel must be configured to allow processes to use a congestion-control algorithm not in the default set; otherwise, it will deny these requests with ``Operation not permitted''. To see which algorithms are available on your system and which are currently permitted for use, look at the contents of the files tcp_available_congestion_control and tcp_allowed_congestion_control in the /proc/sys/net/ipv4 directory.

     As an example, to have Transmission Daemon use the TCP Low Priority congestion-control algorithm (http://www-ece.rice.edu/networks/TCP-LP/), you'll need to modify your kernel configuration to build in support for the algorithm, then update your operating-system configuration to allow its use by adding a sysctl-service-type service (or updating the existing one's configuration) with lines like the following:

          (service sysctl-service-type
                   (sysctl-configuration
                    (settings
                     ("net.ipv4.tcp_allowed_congestion_control" .
                      "reno cubic lp"))))

     The Transmission Daemon configuration can then be updated with

          (peer-congestion-algorithm "lp")

     and the system reconfigured to have the changes take effect.

     Defaults to disabled.

 -- transmission-daemon-configuration parameter: tcp-type-of-service peer-socket-tos
     The type of service to request in outgoing TCP packets, one of default, low-cost, throughput, low-delay and reliability.

     Defaults to default.

 -- transmission-daemon-configuration parameter: non-negative-integer peer-limit-global
     The global limit on the number of connected peers.

     Defaults to 200.

 -- transmission-daemon-configuration parameter: non-negative-integer peer-limit-per-torrent
     The per-torrent limit on the number of connected peers.

     Defaults to 50.

 -- transmission-daemon-configuration parameter: non-negative-integer upload-slots-per-torrent
     The maximum number of peers to which the daemon will upload data simultaneously for each torrent.

     Defaults to 14.

 -- transmission-daemon-configuration parameter: non-negative-integer peer-id-ttl-hours
     The maximum lifespan, in hours, of the peer ID associated with each public torrent before it is regenerated.

     Defaults to 6.

 -- transmission-daemon-configuration parameter: boolean blocklist-enabled?
     When #t, the daemon will ignore peers mentioned in the blocklist it has most recently downloaded from blocklist-url.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: maybe-string blocklist-url
     The URL of a peer blocklist (in P2P-plaintext or eMule .dat format) to be periodically downloaded and applied when blocklist-enabled? is #t.

     Defaults to disabled.

 -- transmission-daemon-configuration parameter: boolean download-queue-enabled?
     If #t, the daemon will be limited to downloading at most download-queue-size non-stalled torrents simultaneously.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: non-negative-integer download-queue-size
     The size of the daemon's download queue, which limits the number of non-stalled torrents it will download at any one time when download-queue-enabled? is #t.

     Defaults to 5.

 -- transmission-daemon-configuration parameter: boolean seed-queue-enabled?
     If #t, the daemon will be limited to seeding at most seed-queue-size non-stalled torrents simultaneously.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: non-negative-integer seed-queue-size
     The size of the daemon's seed queue, which limits the number of non-stalled torrents it will seed at any one time when seed-queue-enabled? is #t.

     Defaults to 10.

 -- transmission-daemon-configuration parameter: boolean queue-stalled-enabled?
     When #t, the daemon will consider torrents for which it has not shared data in the past queue-stalled-minutes minutes to be stalled and not count them against its download-queue-size and seed-queue-size limits.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: non-negative-integer queue-stalled-minutes
     The maximum period, in minutes, a torrent may be idle before it is considered to be stalled, when queue-stalled-enabled? is #t.

     Defaults to 30.

 -- transmission-daemon-configuration parameter: boolean ratio-limit-enabled?
     When #t, a torrent being seeded will automatically be paused once it reaches the ratio specified by ratio-limit.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: non-negative-rational ratio-limit
     The ratio at which a torrent being seeded will be paused, when ratio-limit-enabled? is #t.

     Defaults to 2.0.

 -- transmission-daemon-configuration parameter: boolean idle-seeding-limit-enabled?
     When #t, a torrent being seeded will automatically be paused once it has been idle for idle-seeding-limit minutes.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: non-negative-integer idle-seeding-limit
     The maximum period, in minutes, a torrent being seeded may be idle before it is paused, when idle-seeding-limit-enabled? is #t.

     Defaults to 30.

 -- transmission-daemon-configuration parameter: boolean dht-enabled?
     Enable the distributed hash table (DHT) protocol (http://bittorrent.org/beps/bep_0005.html), which supports the use of trackerless torrents.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: boolean lpd-enabled?
     Enable local peer discovery (https://en.wikipedia.org/wiki/Local_Peer_Discovery) (LPD), which allows the discovery of peers on the local network and may reduce the amount of data sent over the public Internet.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: boolean pex-enabled?
     Enable peer exchange (https://en.wikipedia.org/wiki/Peer_exchange) (PEX), which reduces the daemon's reliance on external trackers and may improve its performance.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: boolean utp-enabled?
     Enable the micro transport protocol (http://bittorrent.org/beps/bep_0029.html) (uTP), which aims to reduce the impact of BitTorrent traffic on other users of the local network while maintaining full utilization of the available bandwidth.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: boolean rpc-enabled?
     If #t, enable the remote procedure call (RPC) interface, which allows remote control of the daemon via its Web interface, the transmission-remote command-line client, and similar tools.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: string rpc-bind-address
     The IP address at which to listen for RPC connections, or ``0.0.0.0'' to listen at all available IP addresses.

     Defaults to "0.0.0.0".

 -- transmission-daemon-configuration parameter: port-number rpc-port
     The port on which to listen for RPC connections.

     Defaults to 9091.

 -- transmission-daemon-configuration parameter: string rpc-url
     The path prefix to use in the RPC-endpoint URL.

     Defaults to "/transmission/".

 -- transmission-daemon-configuration parameter: boolean rpc-authentication-required?
     When #t, clients must authenticate (see rpc-username and rpc-password) when using the RPC interface.  Note this has the side effect of disabling host-name whitelisting (see rpc-host-whitelist-enabled?.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: maybe-string rpc-username
     The username required by clients to access the RPC interface when rpc-authentication-required? is #t.

     Defaults to disabled.

 -- transmission-daemon-configuration parameter: maybe-transmission-password-hash rpc-password
     The password required by clients to access the RPC interface when rpc-authentication-required? is #t.  This must be specified using a password hash in the format recognized by Transmission clients, either copied from an existing settings.json file or generated using the transmission-password-hash procedure.

     Defaults to disabled.

 -- transmission-daemon-configuration parameter: boolean rpc-whitelist-enabled?
     When #t, RPC requests will be accepted only when they originate from an address specified in rpc-whitelist.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: string-list rpc-whitelist
     The list of IP and IPv6 addresses from which RPC requests will be accepted when rpc-whitelist-enabled? is #t.  Wildcards may be specified using *.

     Defaults to '("127.0.0.1" "::1").

 -- transmission-daemon-configuration parameter: boolean rpc-host-whitelist-enabled?
     When #t, RPC requests will be accepted only when they are addressed to a host named in rpc-host-whitelist.  Note that requests to ``localhost'' or ``localhost.'', or to a numeric address, are always accepted regardless of these settings.

     Note also this functionality is disabled when rpc-authentication-required? is #t.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: string-list rpc-host-whitelist
     The list of host names recognized by the RPC server when rpc-host-whitelist-enabled? is #t.

     Defaults to '().

 -- transmission-daemon-configuration parameter: message-level message-level
     The minimum severity level of messages to be logged (to /var/log/transmission.log) by the daemon, one of none (no logging), error, info and debug.

     Defaults to info.

 -- transmission-daemon-configuration parameter: boolean start-added-torrents?
     When #t, torrents are started as soon as they are added; otherwise, they are added in ``paused'' state.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: boolean script-torrent-done-enabled?
     When #t, the script specified by script-torrent-done-filename will be invoked each time a torrent completes.

     Defaults to #f.

 -- transmission-daemon-configuration parameter: maybe-file-object script-torrent-done-filename
     A file name or file-like object specifying a script to run each time a torrent completes, when script-torrent-done-enabled? is #t.

     Defaults to disabled.

 -- transmission-daemon-configuration parameter: boolean scrape-paused-torrents-enabled?
     When #t, the daemon will scrape trackers for a torrent even when the torrent is paused.

     Defaults to #t.

 -- transmission-daemon-configuration parameter: non-negative-integer cache-size-mb
     The amount of memory, in megabytes, to allocate for the daemon's in-memory cache.  A larger value may increase performance by reducing the frequency of disk I/O.

     Defaults to 4.

 -- transmission-daemon-configuration parameter: boolean prefetch-enabled?
     When #t, the daemon will try to improve I/O performance by hinting to the operating system which data is likely to be read next from disk to satisfy requests from peers.

     Defaults to #t.

Monitoring Services
-------------------

Tailon Service
..............

Tailon (https://tailon.readthedocs.io/) is a web application for viewing and searching log files.

The following example will configure the service with default values. By default, Tailon can be accessed on port 8080 (http://localhost:8080).

     (service tailon-service-type)

The following example customises more of the Tailon configuration, adding sed to the list of allowed commands.

     (service tailon-service-type
              (tailon-configuration
                (config-file
                  (tailon-configuration-file
                    (allowed-commands '("tail" "grep" "awk" "sed"))))))

 -- Data Type: tailon-configuration
     Data type representing the configuration of Tailon. This type has the following parameters:

     config-file (default: (tailon-configuration-file))
          The configuration file to use for Tailon.  This can be set to a tailon-configuration-file record value, or any gexp (see G-Expressions).

          For example, to instead use a local file, the local-file function can be used:

               (service tailon-service-type
                        (tailon-configuration
                          (config-file (local-file "./my-tailon.conf"))))

     package (default: tailon)
          The tailon package to use.

 -- Data Type: tailon-configuration-file
     Data type representing the configuration options for Tailon. This type has the following parameters:

     files (default: (list "/var/log"))
          List of files to display.  The list can include strings for a single file or directory, or a list, where the first item is the name of a subsection, and the remaining items are the files or directories in that subsection.

     bind (default: "localhost:8080")
          Address and port to which Tailon should bind on.

     relative-root (default: #f)
          URL path to use for Tailon, set to #f to not use a path.

     allow-transfers? (default: #t)
          Allow downloading the log files in the web interface.

     follow-names? (default: #t)
          Allow tailing of not-yet existent files.

     tail-lines (default: 200)
          Number of lines to read initially from each file.

     allowed-commands (default: (list "tail" "grep" "awk"))
          Commands to allow running.  By default, sed is disabled.

     debug? (default: #f)
          Set debug? to #t to show debug messages.

     wrap-lines (default: #t)
          Initial line wrapping state in the web interface.  Set to #t to initially wrap lines (the default), or to #f to initially not wrap lines.

     http-auth (default: #f)
          HTTP authentication type to use.   Set to #f to disable authentication (the default).  Supported values are "digest" or "basic".

     users (default: #f)
          If HTTP authentication is enabled (see http-auth), access will be restricted to the credentials provided here.  To configure users, use a list of pairs, where the first element of the pair is the username, and the 2nd element of the pair is the password.

               (tailon-configuration-file
                 (http-auth "basic")
                 (users     '(("user1" . "password1")
                              ("user2" . "password2"))))

Darkstat Service
................

Darkstat is a packet sniffer that captures network traffic, calculates statistics about usage, and serves reports over HTTP.

 -- Variable: darkstat-service-type
     This is the service type for the darkstat (https://unix4lyfe.org/darkstat/) service,  its value must be a darkstat-configuration record as in this example:

          (service darkstat-service-type
                   (darkstat-configuration
                     (interface "eno1")))

 -- Data Type: darkstat-configuration
     Data type representing the configuration of darkstat.

     package (default: darkstat)
          The darkstat package to use.

     interface
          Capture traffic on the specified network interface.

     port (default: "667")
          Bind the web interface to the specified port.

     bind-address (default: "127.0.0.1")
          Bind the web interface to the specified address.

     base (default: "/")
          Specify the path of the base URL.  This can be useful if darkstat is accessed via a reverse proxy.

Prometheus Node Exporter Service
................................

The Prometheus ``node exporter'' makes hardware and operating system statistics provided by the Linux kernel available for the Prometheus monitoring system. This service should be deployed on all physical nodes and virtual machines, where monitoring these statistics is desirable.

 -- Variable: prometheus-node-exporter-service-type
     This is the service type for the prometheus-node-exporter (https://github.com/prometheus/node_exporter/) service, its value must be a prometheus-node-exporter-configuration.

          (service prometheus-node-exporter-service-type)

 -- Data Type: prometheus-node-exporter-configuration
     Data type representing the configuration of node_exporter.

     package (default: go-github-com-prometheus-node-exporter)
          The prometheus-node-exporter package to use.

     web-listen-address (default: ":9100")
          Bind the web interface to the specified address.

     textfile-directory (default: "/var/lib/prometheus/node-exporter")
          This directory can be used to export metrics specific to this machine. Files containing metrics in the text format, with the filename ending in .prom should be placed in this directory.

     extra-options (default: '())
          Extra options to pass to the Prometheus node exporter.

vnStat Network Traffic Monitor
..............................

vnStat is a network traffic monitor that uses interface statistics provided by the kernel rather than traffic sniffing.  This makes it a light resource monitor, regardless of network traffic rate.

 -- Variable: vnstat-service-type
     This is the service type for the vnStat (https://humdi.net/vnstat/) daemon and accepts a vnstat-configuration value.

     The following example will configure the service with default values:

          (service vnstat-service-type)

 -- Data Type: vnstat-configuration
     Available vnstat-configuration fields are:

     package (default: vnstat) (type: file-like)
          The vnstat package.

     database-directory (default: "/var/lib/vnstat") (type: string)
          Specifies the directory where the database is to be stored.  A full path must be given and a leading '/' isn't required.

     5-minute-hours (default: 48) (type: maybe-integer)
          Data retention duration for the 5 minute resolution entries.  The configuration defines for how many past hours entries will be stored. Set to -1 for unlimited entries or to 0 to disable the data collection of this resolution.

     64bit-interface-counters (default: -2) (type: maybe-integer)
          Select interface counter handling.  Set to 1 for defining that all interfaces use 64-bit counters on the kernel side and 0 for defining 32-bit counter.  Set to -1 for using the old style logic used in earlier versions where counter values within 32-bits are assumed to be 32-bit and anything larger is assumed to be a 64-bit counter.  This may produce false results if a 64-bit counter is reset within the 32-bits.  Set to -2 for using automatic detection based on available kernel datastructures.

     always-add-new-interfaces? (default: #t) (type: maybe-boolean)
          Enable or disable automatic creation of new database entries for interfaces not currently in the database even if the database file already exists when the daemon is started.  New database entries will also get created for new interfaces seen while the daemon is running. Pseudo interfaces lo, lo0 and sit0 are always excluded from getting added.

     bandwidth-detection? (default: #t) (type: maybe-boolean)
          Try to automatically detect MAX-BANDWIDTH value for each monitored interface.  Mostly only ethernet interfaces support this feature. MAX-BANDWIDTH will be used as fallback value if detection fails. Any interface specific MAX-BW configuration will disable the detection for the specified interface.  In Linux, the detection is disabled for tun interfaces due to the Linux kernel always reporting 10 Mbit regardless of the used real interface.

     bandwidth-detection-interval (default: 5) (type: maybe-integer)
          How often in minutes interface specific detection of MAX-BANDWIDTH is done for detecting possible changes when BANDWIDTH-DETECTION is enabled.  Can be disabled by setting to 0.  Value range: 0..30

     boot-variation (default: 15) (type: maybe-integer)
          Time in seconds how much the boot time reported by system kernel can variate between updates.  Value range: 0..300

     check-disk-space? (default: #t) (type: maybe-boolean)
          Enable or disable the availability check of at least some free disk space before a database write.

     create-directories? (default: #t) (type: maybe-boolean)
          Enable or disable the creation of directories when a configured path doesn't exist.  This includes DATABASE-DIRECTORY.

     daemon-group (type: maybe-user-group)
          Specify the group to which the daemon process should switch during startup.  Set to %unset-value to disable group switching.

     daemon-user (type: maybe-user-account)
          Specify the user to which the daemon process should switch during startup.  Set to %unset-value to disable user switching.

     daily-days (default: 62) (type: maybe-integer)
          Data retention duration for the one day resolution entries.  The configuration defines for how many past days entries will be stored.  Set to -1 for unlimited entries or to 0 to disable the data collection of this resolution.

     database-synchronous (default: -1) (type: maybe-integer)
          Change the setting of the SQLite "synchronous" flag which controls how much care is taken to ensure disk writes have fully completed when writing data to the database before continuing other actions.  Higher values take extra steps to ensure data safety at the cost of slower performance.  A value of 0 will result in all handling being left to the filesystem itself.  Set to -1 to select the default value according to database mode controlled by DATABASE-WRITE-AHEAD-LOGGING setting.  See SQLite documentation for more details regarding values from 1 to 3.  Value range: -1..3

     database-write-ahead-logging? (default: #f) (type: maybe-boolean)
          Enable or disable SQLite Write-Ahead Logging mode for the database.  See SQLite documentation for more details and note that support for read-only operations isn't available in older SQLite versions.

     hourly-days (default: 4) (type: maybe-integer)
          Data retention duration for the one hour resolution entries.  The configuration defines for how many past days entries will be stored.  Set to -1 for unlimited entries or to 0 to disable the data collection of this resolution.

     log-file (type: maybe-string)
          Specify log file path and name to be used if USE-LOGGING is set to 1.

     max-bandwidth (type: maybe-integer)
          Maximum bandwidth for all interfaces.  If the interface specific traffic exceeds the given value then the data is assumed to be invalid and rejected.  Set to 0 in order to disable the feature.  Value range: 0..50000

     max-bw (type: maybe-alist)
          Same as MAX-BANDWIDTH but can be used for setting individual limits for selected interfaces.  This is an association list of interfaces as strings to integer values.  For example,

               (max-bw `(("eth0" .  15000)
                         ("ppp0" .  10000)))

          BANDWIDTH-DETECTION is disabled on an interface specific level for each MAX-BW configuration.  Value range: 0..50000

     monthly-months (default: 25) (type: maybe-integer)
          Data retention duration for the one month resolution entries.  The configuration defines for how many past months entries will be stored. Set to -1 for unlimited entries or to 0 to disable the data collection of this resolution.

     month-rotate (default: 1) (type: maybe-integer)
          Day of month that months are expected to change.  Usually set to 1 but can be set to alternative values for example for tracking monthly billed traffic where the billing period doesn't start on the first day.  For example, if set to 7, days of February up to and including the 6th will count for January.  Changing this option will not cause existing data to be recalculated.  Value range: 1..28

     month-rotate-affects-years? (default: #f) (type: maybe-boolean)
          Enable or disable MONTH-ROTATE also affecting yearly data. Applicable only when MONTH-ROTATE has a value greater than one.

     offline-save-interval (default: 30) (type: maybe-integer)
          How often in minutes cached interface data is saved to file when all monitored interfaces are offline.  Value range: SAVE-INTERVAL..60

     pid-file (default: "/var/run/vnstatd.pid") (type: maybe-string)
          Specify pid file path and name to be used.

     poll-interval (default: 5) (type: maybe-integer)
          How often in seconds interfaces are checked for status changes.  Value range: 2..60

     rescan-database-on-save? (type: maybe-boolean)
          Automatically discover added interfaces from the database and start monitoring.  The rescan is done every SAVE-INTERVAL or OFFLINE-SAVE-INTERVAL minutes depending on the current activity state.

     save-interval (default: 5) (type: maybe-integer)
          How often in minutes cached interface data is saved to file.  Value range: ( UPDATE-INTERVAL / 60 )..60

     save-on-status-change? (default: #t) (type: maybe-boolean)
          Enable or disable the additional saving to file of cached interface data when the availability of an interface changes, i.e., when an interface goes offline or comes online.

     time-sync-wait (default: 5) (type: maybe-integer)
          How many minutes to wait during daemon startup for system clock to sync if most recent database update appears to be in the future.  This may be needed in systems without a real-time clock (RTC) which require some time after boot to query and set the correct time.  0 = wait disabled.  Value range: 0..60

     top-day-entries (default: 20) (type: maybe-integer)
          Data retention duration for the top day entries.  The configuration defines how many of the past top day entries will be stored.  Set to -1 for unlimited entries or to 0 to disable the data collection of this resolution.

     trafficless-entries? (default: #t) (type: maybe-boolean)
          Create database entries even when there is no traffic during the entry's time period.

     update-file-owner? (default: #t) (type: maybe-boolean)
          Enable or disable the update of file ownership during daemon process startup.  During daemon startup, only database, log and pid files will be modified if the user or group change feature ( DAEMON-USER or DAEMON-GROUP ) is enabled and the files don't match the requested user or group.  During manual database creation, this option will cause file ownership to be inherited from the database directory if the directory already exists.  This option only has effect when the process is started as root or via sudo.

     update-interval (default: 20) (type: maybe-integer)
          How often in seconds the interface data is updated.  Value range: POLL-INTERVAL..300

     use-logging (default: 2) (type: maybe-integer)
          Enable or disable logging.  Accepted values are: 0 = disabled, 1 = logfile and 2 = syslog.

     use-utc? (type: maybe-boolean)
          Enable or disable using UTC as timezone in the database for all entries. When enabled, all entries added to the database will use UTC regardless of the configured system timezone.  When disabled, the configured system timezone will be used.  Changing this setting will not result in already existing data to be modified.

     yearly-years (default: -1) (type: maybe-integer)
          Data retention duration for the one year resolution entries.  The configuration defines for how many past years entries will be stored. Set to -1 for unlimited entries or to 0 to disable the data collection of this resolution.

Zabbix server
.............

Zabbix is a high performance monitoring system that can collect data from a variety of sources and provide the results in a web-based interface.  Alerting and reporting is built-in, as well as templates for common operating system metrics such as network utilization, CPU load, and disk space consumption.

This service provides the central Zabbix monitoring service; you also need zabbix-front-end-service-type to configure Zabbix and display results, and optionally zabbix-agent-service-type on machines that should be monitored (other data sources are supported, such as Prometheus Node Exporter).

 -- Variable: zabbix-server-service-type
     This is the service type for the Zabbix server service.  Its value must be a zabbix-server-configuration record, shown below.

 -- Data Type: zabbix-server-configuration
     Available zabbix-server-configuration fields are:

     zabbix-server (default: zabbix-server) (type: file-like)
          The zabbix-server package.

     user (default: "zabbix") (type: string)
          User who will run the Zabbix server.

     group (default: "zabbix") (type: string)
          Group who will run the Zabbix server.

     db-host (default: "127.0.0.1") (type: string)
          Database host name.

     db-name (default: "zabbix") (type: string)
          Database name.

     db-user (default: "zabbix") (type: string)
          Database user.

     db-password (default: "") (type: string)
          Database password.  Please, use include-files with DBPassword=SECRET inside a specified file instead.

     db-port (default: 5432) (type: number)
          Database port.

     log-type (default: "") (type: string)
          Specifies where log messages are written to:

            * system - syslog.

            * file - file specified with log-file parameter.

            * console - standard output.

     log-file (default: "/var/log/zabbix/server.log") (type: string)
          Log file name for log-type file parameter.

     pid-file (default: "/var/run/zabbix/zabbix_server.pid") (type: string)
          Name of PID file.

     ssl-ca-location (default: "/etc/ssl/certs/ca-certificates.crt") (type: string)
          The location of certificate authority (CA) files for SSL server certificate verification.

     ssl-cert-location (default: "/etc/ssl/certs") (type: string)
          Location of SSL client certificates.

     extra-options (default: "") (type: extra-options)
          Extra options will be appended to Zabbix server configuration file.

     include-files (default: '()) (type: include-files)
          You may include individual files or all files in a directory in the configuration file.

Zabbix agent
............

The Zabbix agent gathers information about the running system for the Zabbix monitoring server.  It has a variety of built-in checks, and can be extended with custom user parameters (https://www.zabbix.com/documentation/current/en/manual/config/items/userparameters).

 -- Variable: zabbix-agent-service-type
     This is the service type for the Zabbix agent service.  Its value must be a zabbix-agent-configuration record, shown below.

 -- Data Type: zabbix-agent-configuration
     Available zabbix-agent-configuration fields are:

     zabbix-agent (default: zabbix-agentd) (type: file-like)
          The zabbix-agent package.

     user (default: "zabbix") (type: string)
          User who will run the Zabbix agent.

     group (default: "zabbix") (type: string)
          Group who will run the Zabbix agent.

     hostname (default: "") (type: string)
          Unique, case sensitive hostname which is required for active checks and must match hostname as configured on the server.

     log-type (default: "") (type: string)
          Specifies where log messages are written to:

            * system - syslog.

            * file - file specified with log-file parameter.

            * console - standard output.

     log-file (default: "/var/log/zabbix/agent.log") (type: string)
          Log file name for log-type file parameter.

     pid-file (default: "/var/run/zabbix/zabbix_agent.pid") (type: string)
          Name of PID file.

     server (default: '("127.0.0.1")) (type: list)
          List of IP addresses, optionally in CIDR notation, or hostnames of Zabbix servers and Zabbix proxies.  Incoming connections will be accepted only from the hosts listed here.

     server-active (default: '("127.0.0.1")) (type: list)
          List of IP:port (or hostname:port) pairs of Zabbix servers and Zabbix proxies for active checks.  If port is not specified, default port is used.  If this parameter is not specified, active checks are disabled.

     extra-options (default: "") (type: extra-options)
          Extra options will be appended to Zabbix server configuration file.

     include-files (default: '()) (type: include-files)
          You may include individual files or all files in a directory in the configuration file.

Zabbix front-end
................

The Zabbix front-end provides a web interface to Zabbix.  It does not need to run on the same machine as the Zabbix server.  This service works by extending the PHP-FPM and NGINX services with the configuration necessary for loading the Zabbix user interface.

 -- Variable: zabbix-front-end-service-type
     This is the service type for the Zabbix web frontend.  Its value must be a zabbix-front-end-configuration record, shown below.

 -- Data Type: zabbix-front-end-configuration
     Available zabbix-front-end-configuration fields are:

     zabbix-server (default: zabbix-server) (type: file-like)
          The Zabbix server package to use.

     nginx (default: '()) (type: list)
          List of nginx-server-configuration blocks for the Zabbix front-end.  When empty, a default that listens on port 80 is used.

     db-host (default: "localhost") (type: string)
          Database host name.

     db-port (default: 5432) (type: number)
          Database port.

     db-name (default: "zabbix") (type: string)
          Database name.

     db-user (default: "zabbix") (type: string)
          Database user.

     db-password (default: "") (type: string)
          Database password.  Please, use db-secret-file instead.

     db-secret-file (default: "") (type: string)
          Secret file which will be appended to zabbix.conf.php file.  This file contains credentials for use by Zabbix front-end.  You are expected to create it manually.

     zabbix-host (default: "localhost") (type: string)
          Zabbix server hostname.

     zabbix-port (default: 10051) (type: number)
          Zabbix server port.

Kerberos Services
-----------------

The (gnu services kerberos) module provides services relating to the authentication protocol Kerberos.

Krb5 Service
............

Programs using a Kerberos client library normally expect a configuration file in /etc/krb5.conf. This service generates such a file from a definition provided in the operating system declaration. It does not cause any daemon to be started.

No ``keytab'' files are provided by this service---you must explicitly create them. This service is known to work with the MIT client library, mit-krb5. Other implementations have not been tested.

 -- Variable: krb5-service-type
     A service type for Kerberos 5 clients.

Here is an example of its use:

     (service krb5-service-type
              (krb5-configuration
               (default-realm "EXAMPLE.COM")
               (allow-weak-crypto? #t)
               (realms (list
                        (krb5-realm
                         (name "EXAMPLE.COM")
                         (admin-server "groucho.example.com")
                         (kdc "karl.example.com"))
                        (krb5-realm
                         (name "ARGRX.EDU")
                         (admin-server "kerb-admin.argrx.edu")
                         (kdc "keys.argrx.edu"))))))

This example provides a Kerberos 5 client configuration which:

  * Recognizes two realms, viz: ``EXAMPLE.COM'' and ``ARGRX.EDU'', both of which have distinct administration servers and key distribution centers;

  * Will default to the realm ``EXAMPLE.COM'' if the realm is not explicitly specified by clients;

  * Accepts services which only support encryption types known to be weak.

The krb5-realm and krb5-configuration types have many fields. Only the most commonly used ones are described here. For a full list, and more detailed explanation of each, see the MIT krb5.conf documentation.

 -- Data Type: krb5-realm

     name
          This field is a string identifying the name of the realm. A common convention is to use the fully qualified DNS name of your organization, converted to upper case.

     admin-server
          This field is a string identifying the host where the administration server is running.

     kdc
          This field is a string identifying the key distribution center for the realm.

 -- Data Type: krb5-configuration

     allow-weak-crypto? (default: #f)
          If this flag is #t then services which only offer encryption algorithms known to be weak will be accepted.

     default-realm (default: #f)
          This field should be a string identifying the default Kerberos realm for the client. You should set this field to the name of your Kerberos realm. If this value is #f then a realm must be specified with every Kerberos principal when invoking programs such as kinit.

     realms
          This should be a non-empty list of krb5-realm objects, which clients may access. Normally, one of them will have a name field matching the default-realm field.

PAM krb5 Service
................

The pam-krb5 service allows for login authentication and password management via Kerberos. You will need this service if you want PAM enabled applications to authenticate users using Kerberos.

 -- Variable: pam-krb5-service-type
     A service type for the Kerberos 5 PAM module.

 -- Data Type: pam-krb5-configuration
     Data type representing the configuration of the Kerberos 5 PAM module. This type has the following parameters:

     pam-krb5 (default: pam-krb5)
          The pam-krb5 package to use.

     minimum-uid (default: 1000)
          The smallest user ID for which Kerberos authentications should be attempted. Local accounts with lower values will silently fail to authenticate.

LDAP Services
-------------

Authentication against LDAP with nslcd
......................................

The (gnu services authentication) module provides the nslcd-service-type, which can be used to authenticate against an LDAP server.  In addition to configuring the service itself, you may want to add ldap as a name service to the Name Service Switch. See Name Service Switch for detailed information.

Here is a simple operating system declaration with a default configuration of the nslcd-service-type and a Name Service Switch configuration that consults the ldap name service last:

     (use-service-modules authentication)
     (use-modules (gnu system nss))
     ...
     (operating-system
       ...
       (services
         (cons*
           (service nslcd-service-type)
           (service dhcp-client-service-type)
           %base-services))
       (name-service-switch
        (let ((services (list (name-service (name "db"))
                              (name-service (name "files"))
                              (name-service (name "ldap")))))
          (name-service-switch
           (inherit %mdns-host-lookup-nss)
           (password services)
           (shadow   services)
           (group    services)
           (netgroup services)
           (gshadow  services)))))

Available nslcd-configuration fields are:

 -- nslcd-configuration parameter: package nss-pam-ldapd
     The nss-pam-ldapd package to use.

 -- nslcd-configuration parameter: maybe-number threads
     The number of threads to start that can handle requests and perform LDAP queries.  Each thread opens a separate connection to the LDAP server. The default is to start 5 threads.

     Defaults to disabled.

 -- nslcd-configuration parameter: string uid
     This specifies the user id with which the daemon should be run.

     Defaults to "nslcd".

 -- nslcd-configuration parameter: string gid
     This specifies the group id with which the daemon should be run.

     Defaults to "nslcd".

 -- nslcd-configuration parameter: log-option log
     This option controls the way logging is done via a list containing SCHEME and LEVEL.  The SCHEME argument may either be the symbols none or syslog, or an absolute file name.  The LEVEL argument is optional and specifies the log level.  The log level may be one of the following symbols: crit, error, warning, notice, info or debug.  All messages with the specified log level or higher are logged.

     Defaults to '("/var/log/nslcd" info).

 -- nslcd-configuration parameter: list uri
     The list of LDAP server URIs.  Normally, only the first server will be used with the following servers as fall-back.

     Defaults to '("ldap://localhost:389/").

 -- nslcd-configuration parameter: maybe-string ldap-version
     The version of the LDAP protocol to use.  The default is to use the maximum version supported by the LDAP library.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string binddn
     Specifies the distinguished name with which to bind to the directory server for lookups.  The default is to bind anonymously.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string bindpw
     Specifies the credentials with which to bind.  This option is only applicable when used with binddn.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string rootpwmoddn
     Specifies the distinguished name to use when the root user tries to modify a user's password using the PAM module.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string rootpwmodpw
     Specifies the credentials with which to bind if the root user tries to change a user's password.  This option is only applicable when used with rootpwmoddn

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string sasl-mech
     Specifies the SASL mechanism to be used when performing SASL authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string sasl-realm
     Specifies the SASL realm to be used when performing SASL authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string sasl-authcid
     Specifies the authentication identity to be used when performing SASL authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string sasl-authzid
     Specifies the authorization identity to be used when performing SASL authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-boolean sasl-canonicalize?
     Determines whether the LDAP server host name should be canonicalised.  If this is enabled the LDAP library will do a reverse host name lookup.  By default, it is left up to the LDAP library whether this check is performed or not.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string krb5-ccname
     Set the name for the GSS-API Kerberos credentials cache.

     Defaults to disabled.

 -- nslcd-configuration parameter: string base
     The directory search base.

     Defaults to "dc=example,dc=com".

 -- nslcd-configuration parameter: scope-option scope
     Specifies the search scope (subtree, onelevel, base or children).  The default scope is subtree; base scope is almost never useful for name service lookups; children scope is not supported on all servers.

     Defaults to '(subtree).

 -- nslcd-configuration parameter: maybe-deref-option deref
     Specifies the policy for dereferencing aliases.  The default policy is to never dereference aliases.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-boolean referrals
     Specifies whether automatic referral chasing should be enabled.  The default behaviour is to chase referrals.

     Defaults to disabled.

 -- nslcd-configuration parameter: list-of-map-entries maps
     This option allows for custom attributes to be looked up instead of the default RFC 2307 attributes.  It is a list of maps, each consisting of the name of a map, the RFC 2307 attribute to match and the query expression for the attribute as it is available in the directory.

     Defaults to '().

 -- nslcd-configuration parameter: list-of-filter-entries filters
     A list of filters consisting of the name of a map to which the filter applies and an LDAP search filter expression.

     Defaults to '().

 -- nslcd-configuration parameter: maybe-number bind-timelimit
     Specifies the time limit in seconds to use when connecting to the directory server.  The default value is 10 seconds.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number timelimit
     Specifies the time limit (in seconds) to wait for a response from the LDAP server.  A value of zero, which is the default, is to wait indefinitely for searches to be completed.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number idle-timelimit
     Specifies the period if inactivity (in seconds) after which the con‐ nection to the LDAP server will be closed.  The default is not to time out connections.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number reconnect-sleeptime
     Specifies the number of seconds to sleep when connecting to all LDAP servers fails.  By default one second is waited between the first failure and the first retry.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number reconnect-retrytime
     Specifies the time after which the LDAP server is considered to be permanently unavailable.  Once this time is reached retries will be done only once per this time period.  The default value is 10 seconds.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-ssl-option ssl
     Specifies whether to use SSL/TLS or not (the default is not to).  If 'start-tls is specified then StartTLS is used rather than raw LDAP over SSL.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-tls-reqcert-option tls-reqcert
     Specifies what checks to perform on a server-supplied certificate.  The meaning of the values is described in the ldap.conf(5) manual page.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string tls-cacertdir
     Specifies the directory containing X.509 certificates for peer authen‐ tication.  This parameter is ignored when using GnuTLS.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string tls-cacertfile
     Specifies the path to the X.509 certificate for peer authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string tls-randfile
     Specifies the path to an entropy source.  This parameter is ignored when using GnuTLS.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string tls-ciphers
     Specifies the ciphers to use for TLS as a string.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string tls-cert
     Specifies the path to the file containing the local certificate for client TLS authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string tls-key
     Specifies the path to the file containing the private key for client TLS authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number pagesize
     Set this to a number greater than 0 to request paged results from the LDAP server in accordance with RFC2696.  The default (0) is to not request paged results.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-ignore-users-option nss-initgroups-ignoreusers
     This option prevents group membership lookups through LDAP for the specified users.  Alternatively, the value 'all-local may be used.  With that value nslcd builds a full list of non-LDAP users on startup.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number nss-min-uid
     This option ensures that LDAP users with a numeric user id lower than the specified value are ignored.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number nss-uid-offset
     This option specifies an offset that is added to all LDAP numeric user ids.  This can be used to avoid user id collisions with local users.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-number nss-gid-offset
     This option specifies an offset that is added to all LDAP numeric group ids.  This can be used to avoid user id collisions with local groups.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-boolean nss-nested-groups
     If this option is set, the member attribute of a group may point to another group.  Members of nested groups are also returned in the higher level group and parent groups are returned when finding groups for a specific user.  The default is not to perform extra searches for nested groups.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-boolean nss-getgrent-skipmembers
     If this option is set, the group member list is not retrieved when looking up groups.  Lookups for finding which groups a user belongs to will remain functional so the user will likely still get the correct groups assigned on login.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-boolean nss-disable-enumeration
     If this option is set, functions which cause all user/group entries to be loaded from the directory will not succeed in doing so.  This can dramatically reduce LDAP server load in situations where there are a great number of users and/or groups.  This option is not recommended for most configurations.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string validnames
     This option can be used to specify how user and group names are verified within the system.  This pattern is used to check all user and group names that are requested and returned from LDAP.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-boolean ignorecase
     This specifies whether or not to perform searches using case-insensitive matching.  Enabling this could open up the system to authorization bypass vulnerabilities and introduce nscd cache poisoning vulnerabilities which allow denial of service.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-boolean pam-authc-ppolicy
     This option specifies whether password policy controls are requested and handled from the LDAP server when performing user authentication.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string pam-authc-search
     By default nslcd performs an LDAP search with the user's credentials after BIND (authentication) to ensure that the BIND operation was successful.  The default search is a simple check to see if the user's DN exists.  A search filter can be specified that will be used instead. It should return at least one entry.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string pam-authz-search
     This option allows flexible fine tuning of the authorisation check that should be performed.  The search filter specified is executed and if any entries match, access is granted, otherwise access is denied.

     Defaults to disabled.

 -- nslcd-configuration parameter: maybe-string pam-password-prohibit-message
     If this option is set password modification using pam_ldap will be denied and the specified message will be presented to the user instead. The message can be used to direct the user to an alternative means of changing their password.

     Defaults to disabled.

 -- nslcd-configuration parameter: list pam-services
     List of pam service names for which LDAP authentication should suffice.

     Defaults to '().

LDAP Directory Server
.....................

The (gnu services ldap) module provides the directory-server-service-type, which can be used to create and launch an LDAP server instance.

Here is an example configuration of the directory-server-service-type:

     (use-service-modules ldap)

     ...
     (operating-system
       ...
       (services
         (cons
           (service directory-server-service-type
                    (directory-server-instance-configuration
                     (slapd
                      (slapd-configuration
                       (root-password "{PBKDF2_SHA256}AAAgAG...ABSOLUTELYSECRET")))))
           %base-services)))

The root password should be generated with the pwdhash utility that is provided by the 389-ds-base package.

Note that changes to the directory server configuration will not be applied to existing instances.  You will need to back up and restore server data manually.  Only new directory server instances will be created upon system reconfiguration.

 -- Data Type: directory-server-instance-configuration
     Available directory-server-instance-configuration fields are:

     package (default: 389-ds-base) (type: file-like)
          The 389-ds-base package.

     config-version (default: 2) (type: number)
          Sets the format version of the configuration file.  To use the INF file with dscreate, this parameter must be 2.

     full-machine-name (default: "localhost") (type: string)
          Sets the fully qualified hostname (FQDN) of this system.

     selinux (default: #false) (type: boolean)
          Enables SELinux detection and integration during the installation of this instance.  If set to #true, dscreate auto-detects whether SELinux is enabled.

     strict-host-checking (default: #true) (type: boolean)
          Sets whether the server verifies the forward and reverse record set in the full-machine-name parameter.  When installing this instance with GSSAPI authentication behind a load balancer, set this parameter to #false.

     systemd (default: #false) (type: boolean)
          Enables systemd platform features.  If set to #true, dscreate auto-detects whether systemd is installed.

     slapd (type: slapd-configuration)
          Configuration of slapd.

           -- Data Type: slapd-configuration
               Available slapd-configuration fields are:

               instance-name (default: "localhost") (type: string)
                    Sets the name of the instance.  You can refer to this value in other parameters of this INF file using the {instance_name} variable. Note that this name cannot be changed after the installation!

               user (default: "dirsrv") (type: string)
                    Sets the user name the ns-slapd process will use after the service started.

               group (default: "dirsrv") (type: string)
                    Sets the group name the ns-slapd process will use after the service started.

               port (default: 389) (type: number)
                    Sets the TCP port the instance uses for LDAP connections.

               secure-port (default: 636) (type: number)
                    Sets the TCP port the instance uses for TLS-secured LDAP connections (LDAPS).

               root-dn (default: "cn=Directory Manager") (type: string)
                    Sets the Distinquished Name (DN) of the administrator account for this instance.

               root-password (default: "{invalid}YOU-SHOULD-CHANGE-THIS") (type: string)
                    Sets the password of the account specified in the root-dn parameter.  You can either set this parameter to a plain text password dscreate hashes during the installation or to a "{algorithm}hash" string generated by the pwdhash utility. Note that setting a plain text password can be a security risk if unprivileged users can read this INF file!

               self-sign-cert (default: #true) (type: boolean)
                    Sets whether the setup creates a self-signed certificate and enables TLS encryption during the installation.  This is not suitable for production, but it enables administrators to use TLS right after the installation.  You can replace the self-signed certificate with a certificate issued by a certificate authority.

               self-sign-cert-valid-months (default: 24) (type: number)
                    Set the number of months the issued self-signed certificate will be valid.

               backup-dir (default: "/var/lib/dirsrv/slapd-{instance_name}/bak") (type: string)
                    Set the backup directory of the instance.

               cert-dir (default: "/etc/dirsrv/slapd-{instance_name}") (type: string)
                    Sets the directory of the instance's Network Security Services (NSS) database.

               config-dir (default: "/etc/dirsrv/slapd-{instance_name}") (type: string)
                    Sets the configuration directory of the instance.

               db-dir (default: "/var/lib/dirsrv/slapd-{instance_name}/db") (type: string)
                    Sets the database directory of the instance.

               initconfig-dir (default: "/etc/dirsrv/registry") (type: string)
                    Sets the directory of the operating system's rc configuration directory.

               ldif-dir (default: "/var/lib/dirsrv/slapd-{instance_name}/ldif") (type: string)
                    Sets the LDIF export and import directory of the instance.

               lock-dir (default: "/var/lock/dirsrv/slapd-{instance_name}") (type: string)
                    Sets the lock directory of the instance.

               log-dir (default: "/var/log/dirsrv/slapd-{instance_name}") (type: string)
                    Sets the log directory of the instance.

               run-dir (default: "/run/dirsrv") (type: string)
                    Sets PID directory of the instance.

               schema-dir (default: "/etc/dirsrv/slapd-{instance_name}/schema") (type: string)
                    Sets schema directory of the instance.

               tmp-dir (default: "/tmp") (type: string)
                    Sets the temporary directory of the instance.

     backend-userroot (type: backend-userroot-configuration)
          Configuration of the userroot backend.

           -- Data Type: backend-userroot-configuration
               Available backend-userroot-configuration fields are:

               create-suffix-entry? (default: #false) (type: boolean)
                    Set this parameter to #true to create a generic root node entry for the suffix in the database.

               require-index? (default: #false) (type: boolean)
                    Set this parameter to #true to refuse unindexed searches in this database.

               sample-entries (default: "no") (type: string)
                    Set this parameter to "yes" to add latest version of sample entries to this database.  Or, use "001003006" to use the 1.3.6 version sample entries.  Use this option, for example, to create a database for testing purposes.

               suffix (type: maybe-string)
                    Sets the root suffix stored in this database.  If you do not set the suffix attribute the install process will not create the backend/suffix. You can also create multiple backends/suffixes by duplicating this section.

Web Services
------------

The (gnu services web) module provides the Apache HTTP Server, the nginx web server, and also a fastcgi wrapper daemon.

Apache HTTP Server
..................

 -- Variable: httpd-service-type
     Service type for the Apache HTTP (https://httpd.apache.org/) server (httpd).  The value for this service type is a httpd-configuration record.

     A simple example configuration is given below.

          (service httpd-service-type
                   (httpd-configuration
                     (config
                       (httpd-config-file
                         (server-name "www.example.com")
                         (document-root "/srv/http/www.example.com")))))

     Other services can also extend the httpd-service-type to add to the configuration.

          (simple-service 'www.example.com-server httpd-service-type
                          (list
                            (httpd-virtualhost
                              "*:80"
                              (list (string-join '("ServerName www.example.com"
                                                   "DocumentRoot /srv/http/www.example.com")
                                                 "\n")))))

The details for the httpd-configuration, httpd-module, httpd-config-file and httpd-virtualhost record types are given below.

 -- Data Type: httpd-configuration
     This data type represents the configuration for the httpd service.

     package (default: httpd)
          The httpd package to use.

     pid-file (default: "/var/run/httpd")
          The pid file used by the shepherd-service.

     config (default: (httpd-config-file))
          The configuration file to use with the httpd service.  The default value is a httpd-config-file record, but this can also be a different G-expression that generates a file, for example a plain-file.  A file outside of the store can also be specified through a string.

 -- Data Type: httpd-module
     This data type represents a module for the httpd service.

     name
          The name of the module.

     file
          The file for the module.  This can be relative to the httpd package being used, the absolute location of a file, or a G-expression for a file within the store, for example (file-append mod-wsgi "/modules/mod_wsgi.so").

 -- Variable: %default-httpd-modules
     A default list of httpd-module objects.

 -- Data Type: httpd-config-file
     This data type represents a configuration file for the httpd service.

     modules (default: %default-httpd-modules)
          The modules to load.  Additional modules can be added here, or loaded by additional configuration.

          For example, in order to handle requests for PHP files, you can use Apache’s mod_proxy_fcgi module along with php-fpm-service-type:

               (service httpd-service-type
                        (httpd-configuration
                         (config
                          (httpd-config-file
                           (modules (cons*
                                     (httpd-module
                                      (name "proxy_module")
                                      (file "modules/mod_proxy.so"))
                                     (httpd-module
                                      (name "proxy_fcgi_module")
                                      (file "modules/mod_proxy_fcgi.so"))
                                     %default-httpd-modules))
                           (extra-config (list "\
               <FilesMatch \\.php$>
                   SetHandler \"proxy:unix:/var/run/php-fpm.sock|fcgi://localhost/\"
               </FilesMatch>"))))))
               (service php-fpm-service-type
                        (php-fpm-configuration
                         (socket "/var/run/php-fpm.sock")
                         (socket-group "httpd")))

     server-root (default: httpd)
          The ServerRoot in the configuration file, defaults to the httpd package.  Directives including Include and LoadModule are taken as relative to the server root.

     server-name (default: #f)
          The ServerName in the configuration file, used to specify the request scheme, hostname and port that the server uses to identify itself.

          This doesn't need to be set in the server config, and can be specified in virtual hosts.  The default is #f to not specify a ServerName.

     document-root (default: "/srv/http")
          The DocumentRoot from which files will be served.

     listen (default: '("80"))
          The list of values for the Listen directives in the config file.  The value should be a list of strings, when each string can specify the port number to listen on, and optionally the IP address and protocol to use.

     pid-file (default: "/var/run/httpd")
          The PidFile to use.  This should match the pid-file set in the httpd-configuration so that the Shepherd service is configured correctly.

     error-log (default: "/var/log/httpd/error_log")
          The ErrorLog to which the server will log errors.

     user (default: "httpd")
          The User which the server will answer requests as.

     group (default: "httpd")
          The Group which the server will answer requests as.

     extra-config (default: (list "TypesConfig etc/httpd/mime.types"))
          A flat list of strings and G-expressions which will be added to the end of the configuration file.

          Any values which the service is extended with will be appended to this list.

 -- Data Type: httpd-virtualhost
     This data type represents a virtualhost configuration block for the httpd service.

     These should be added to the extra-config for the httpd-service.

          (simple-service 'www.example.com-server httpd-service-type
                          (list
                            (httpd-virtualhost
                              "*:80"
                              (list (string-join '("ServerName www.example.com"
                                                    "DocumentRoot /srv/http/www.example.com")
                                                 "\n")))))

     addresses-and-ports
          The addresses and ports for the VirtualHost directive.

     contents
          The contents of the VirtualHost directive, this should be a list of strings and G-expressions.

NGINX
.....

 -- Variable: nginx-service-type
     Service type for the NGinx (https://nginx.org/) web server.  The value for this service type is a <nginx-configuration> record.

     A simple example configuration is given below.

          (service nginx-service-type
                   (nginx-configuration
                     (server-blocks
                       (list (nginx-server-configuration
                               (server-name '("www.example.com"))
                               (root "/srv/http/www.example.com"))))))

     In addition to adding server blocks to the service configuration directly, this service can be extended by other services to add server blocks, as in this example:

          (simple-service 'my-extra-server nginx-service-type
                          (list (nginx-server-configuration
                                  (root "/srv/http/extra-website")
                                  (try-files (list "$uri" "$uri/index.html")))))

At startup, nginx has not yet read its configuration file, so it uses a default file to log error messages.  If it fails to load its configuration file, that is where error messages are logged.  After the configuration file is loaded, the default error log file changes as per configuration.  In our case, startup error messages can be found in /var/run/nginx/logs/error.log, and after configuration in /var/log/nginx/error.log.  The second location can be changed with the LOG-DIRECTORY configuration option.

 -- Data Type: nginx-configuration
     This data type represents the configuration for NGinx.  Some configuration can be done through this and the other provided record types, or alternatively, a config file can be provided.

     nginx (default: nginx)
          The nginx package to use.

     shepherd-requirement (default: '())
          This is a list of symbols naming Shepherd services the nginx service will depend on.

          This is useful if you would like nginx to be started after a back-end web server or a logging service such as Anonip has been started.

     log-directory (default: "/var/log/nginx")
          The directory to which NGinx will write log files.

     log-level (default: 'error) (type: symbol)
          Logging level, which can be any of the following values: 'debug, 'info, 'notice, 'warn, 'error, 'crit, 'alert, or 'emerg.

     run-directory (default: "/var/run/nginx")
          The directory in which NGinx will create a pid file, and write temporary files.

     server-blocks (default: '())
          A list of server blocks to create in the generated configuration file, the elements should be of type <nginx-server-configuration>.

          The following example would setup NGinx to serve www.example.com from the /srv/http/www.example.com directory, without using HTTPS.

               (service nginx-service-type
                        (nginx-configuration
                          (server-blocks
                            (list (nginx-server-configuration
                                    (server-name '("www.example.com"))
                                    (root "/srv/http/www.example.com"))))))

     upstream-blocks (default: '())
          A list of upstream blocks to create in the generated configuration file, the elements should be of type <nginx-upstream-configuration>.

          Configuring upstreams through the upstream-blocks can be useful when combined with locations in the <nginx-server-configuration> records.  The following example creates a server configuration with one location configuration, that will proxy requests to a upstream configuration, which will handle requests with two servers.

               (service
                 nginx-service-type
                 (nginx-configuration
                   (server-blocks
                     (list (nginx-server-configuration
                             (server-name '("www.example.com"))
                             (root "/srv/http/www.example.com")
                             (locations
                               (list
                                 (nginx-location-configuration
                                 (uri "/path1")
                                 (body '("proxy_pass http://server-proxy;"))))))))
                   (upstream-blocks
                     (list (nginx-upstream-configuration
                             (name "server-proxy")
                             (servers (list "server1.example.com"
                                            "server2.example.com")))))))

     file (default: #f)
          If a configuration FILE is provided, this will be used, rather than generating a configuration file from the provided log-directory, run-directory, server-blocks and upstream-blocks.  For proper operation, these arguments should match what is in FILE to ensure that the directories are created when the service is activated.

          This can be useful if you have an existing configuration file, or it's not possible to do what is required through the other parts of the nginx-configuration record.

     server-names-hash-bucket-size (default: #f)
          Bucket size for the server names hash tables, defaults to #f to use the size of the processors cache line.

     server-names-hash-bucket-max-size (default: #f)
          Maximum bucket size for the server names hash tables.

     modules (default: '())
          List of nginx dynamic modules to load.  This should be a list of file names of loadable modules, as in this example:

               (modules
                (list
                 (file-append nginx-accept-language-module "\
               /etc/nginx/modules/ngx_http_accept_language_module.so")
                 (file-append nginx-lua-module "\
               /etc/nginx/modules/ngx_http_lua_module.so")))

     lua-package-path (default: '())
          List of nginx lua packages to load.  This should be a list of package names of loadable lua modules, as in this example:

               (lua-package-path (list lua-resty-core
                                       lua-resty-lrucache
                                       lua-resty-signal
                                       lua-tablepool
                                       lua-resty-shell))

     lua-package-cpath (default: '())
          List of nginx lua C packages to load.  This should be a list of package names of loadable lua C modules, as in this example:

               (lua-package-cpath (list lua-resty-signal))

     global-directives (default: '((events . ())))
          Association list of global directives for the top level of the nginx configuration.  Values may themselves be association lists.

               (global-directives
                `((worker_processes . 16)
                  (pcre_jit . on)
                  (events . ((worker_connections . 1024)))))

     extra-content (default: "")
          Extra content for the http block.  Should be string or a string valued G-expression.

 -- Data Type: nginx-server-configuration
     Data type representing the configuration of an nginx server block. This type has the following parameters:

     listen (default: '("80" "443 ssl"))
          Each listen directive sets the address and port for IP, or the path for a UNIX-domain socket on which the server will accept requests. Both address and port, or only address or only port can be specified. An address may also be a hostname, for example:

               '("127.0.0.1:8000" "127.0.0.1" "8000" "*:8000" "localhost:8000")

     server-name (default: (list 'default))
          A list of server names this server represents. 'default represents the default server for connections matching no other server.

     root (default: "/srv/http")
          Root of the website nginx will serve.

     locations (default: '())
          A list of nginx-location-configuration or nginx-named-location-configuration records to use within this server block.

     index (default: (list "index.html"))
          Index files to look for when clients ask for a directory.  If it cannot be found, Nginx will send the list of files in the directory.

     try-files (default: '())
          A list of files whose existence is checked in the specified order. nginx will use the first file it finds to process the request.

     ssl-certificate (default: #f)
          Where to find the certificate for secure connections.  Set it to #f if you don't have a certificate or you don't want to use HTTPS.

     ssl-certificate-key (default: #f)
          Where to find the private key for secure connections.  Set it to #f if you don't have a key or you don't want to use HTTPS.

     server-tokens? (default: #f)
          Whether the server should add its configuration to response.

     raw-content (default: '())
          A list of raw lines added to the server block.

 -- Data Type: nginx-upstream-configuration
     Data type representing the configuration of an nginx upstream block.  This type has the following parameters:

     name
          Name for this group of servers.

     servers
          Specify the addresses of the servers in the group.  The address can be specified as a IP address (e.g. 127.0.0.1), domain name (e.g. backend1.example.com) or a path to a UNIX socket using the prefix unix:.  For addresses using an IP address or domain name, the default port is 80, and a different port can be specified explicitly.

     extra-content
          A string or list of strings to add to the upstream block.

 -- Data Type: nginx-location-configuration
     Data type representing the configuration of an nginx location block.  This type has the following parameters:

     uri
          URI which this location block matches.

     body
          Body of the location block, specified as a list of strings.  This can contain many configuration directives.  For example, to pass requests to a upstream server group defined using an nginx-upstream-configuration block, the following directive would be specified in the body (list "proxy_pass http://upstream-name;").

 -- Data Type: nginx-named-location-configuration
     Data type representing the configuration of an nginx named location block.  Named location blocks are used for request redirection, and not used for regular request processing.  This type has the following parameters:

     name
          Name to identify this location block.

     body
          See nginx-location-configuration body, as the body for named location blocks can be used in a similar way to the nginx-location-configuration body.  One restriction is that the body of a named location block cannot contain location blocks.

Varnish Cache
.............

Varnish is a fast cache server that sits in between web applications and end users.  It proxies requests from clients and caches the accessed URLs such that multiple requests for the same resource only creates one request to the back-end.

 -- Variable: varnish-service-type
     Service type for the Varnish daemon.

 -- Data Type: varnish-configuration
     Data type representing the varnish service configuration. This type has the following parameters:

     package (default: varnish)
          The Varnish package to use.

     name (default: "default")
          A name for this Varnish instance.  Varnish will create a directory in /var/varnish/ with this name and keep temporary files there.  If the name starts with a forward slash, it is interpreted as an absolute directory name.

          Pass the -n argument to other Varnish programs to connect to the named instance, e.g. varnishncsa -n default.

     backend (default: "localhost:8080")
          The backend to use.  This option has no effect if vcl is set.

     vcl (default: #f)
          The VCL (Varnish Configuration Language) program to run.  If this is #f, Varnish will proxy backend using the default configuration.  Otherwise this must be a file-like object with valid VCL syntax.

          For example, to mirror www.gnu.org (https://www.gnu.org) with VCL you can do something along these lines:

               (define %gnu-mirror
                 (plain-file "gnu.vcl"
                             "vcl 4.1;
               backend gnu { .host = \"www.gnu.org\"; }"))

               (operating-system
                 ;; ...
                 (services (cons (service varnish-service-type
                                          (varnish-configuration
                                           (listen '(":80"))
                                           (vcl %gnu-mirror)))
                                 %base-services)))

          The configuration of an already running Varnish instance can be inspected and changed using the varnishadm program.

          Consult the Varnish User Guide (https://varnish-cache.org/docs/) and Varnish Book (https://book.varnish-software.com/4.0/) for comprehensive documentation on Varnish and its configuration language.

     listen (default: '("localhost:80"))
          List of addresses Varnish will listen on.

     storage (default: '("malloc,128m"))
          List of storage backends that will be available in VCL.

     parameters (default: '())
          List of run-time parameters in the form '(("parameter" . "value")).

     extra-options (default: '())
          Additional arguments to pass to the varnishd process.

Patchwork
.........

Patchwork is a patch tracking system.  It can collect patches sent to a mailing list, and display them in a web interface.

 -- Variable: patchwork-service-type
     Service type for Patchwork.

The following example is an example of a minimal service for Patchwork, for the patchwork.example.com domain.

     (service patchwork-service-type
              (patchwork-configuration
               (domain "patchwork.example.com")
               (settings-module
                (patchwork-settings-module
                 (allowed-hosts (list domain))
                 (default-from-email "patchwork@patchwork.example.com")))
               (getmail-retriever-config
                (getmail-retriever-configuration
                 (type "SimpleIMAPSSLRetriever")
                 (server "imap.example.com")
                 (port 993)
                 (username "patchwork")
                 (password-command
                  (list (file-append coreutils "/bin/cat")
                        "/etc/getmail-patchwork-imap-password"))
                 (extra-parameters
                 '((mailboxes . ("Patches"))))))))

There are three records for configuring the Patchwork service.  The <patchwork-configuration> relates to the configuration for Patchwork within the HTTPD service.

The settings-module field within the <patchwork-configuration> record can be populated with the <patchwork-settings-module> record, which describes a settings module that is generated within the Guix store.

For the database-configuration field within the <patchwork-settings-module>, the <patchwork-database-configuration> must be used.

 -- Data Type: patchwork-configuration
     Data type representing the Patchwork service configuration.  This type has the following parameters:

     patchwork (default: patchwork)
          The Patchwork package to use.

     domain
          The domain to use for Patchwork, this is used in the HTTPD service virtual host.

     settings-module
          The settings module to use for Patchwork.  As a Django application, Patchwork is configured with a Python module containing the settings.  This can either be an instance of the <patchwork-settings-module> record, any other record that represents the settings in the store, or a directory outside of the store.

     static-path  (default: "/static/")
          The path under which the HTTPD service should serve the static files.

     getmail-retriever-config
          The getmail-retriever-configuration record value to use with Patchwork.  Getmail will be configured with this value, the messages will be delivered to Patchwork.

 -- Data Type: patchwork-settings-module
     Data type representing a settings module for Patchwork.  Some of these settings relate directly to Patchwork, but others relate to Django, the web framework used by Patchwork, or the Django Rest Framework library.  This type has the following parameters:

     database-configuration (default: (patchwork-database-configuration))
          The database connection settings used for Patchwork.  See the <patchwork-database-configuration> record type for more information.

     secret-key-file (default: "/etc/patchwork/django-secret-key")
          Patchwork, as a Django web application uses a secret key for cryptographically signing values.  This file should contain a unique unpredictable value.

          If this file does not exist, it will be created and populated with a random value by the patchwork-setup shepherd service.

          This setting relates to Django.

     allowed-hosts
          A list of valid hosts for this Patchwork service.  This should at least include the domain specified in the <patchwork-configuration> record.

          This is a Django setting.

     default-from-email
          The email address from which Patchwork should send email by default.

          This is a Patchwork setting.

     static-url (default: #f)
          The URL to use when serving static assets.  It can be part of a URL, or a full URL, but must end in a /.

          If the default value is used, the static-path value from the <patchwork-configuration> record will be used.

          This is a Django setting.

     admins (default: '())
          Email addresses to send the details of errors that occur.  Each value should be a list containing two elements, the name and then the email address.

          This is a Django setting.

     debug? (default: #f)
          Whether to run Patchwork in debug mode.  If set to #t, detailed error messages will be shown.

          This is a Django setting.

     enable-rest-api? (default: #t)
          Whether to enable the Patchwork REST API.

          This is a Patchwork setting.

     enable-xmlrpc? (default: #t)
          Whether to enable the XML RPC API.

          This is a Patchwork setting.

     force-https-links? (default: #t)
          Whether to use HTTPS links on Patchwork pages.

          This is a Patchwork setting.

     extra-settings (default: "")
          Extra code to place at the end of the Patchwork settings module.

 -- Data Type: patchwork-database-configuration
     Data type representing the database configuration for Patchwork.

     engine (default: "django.db.backends.postgresql_psycopg2")
          The database engine to use.

     name (default: "patchwork")
          The name of the database to use.

     user (default: "httpd")
          The user to connect to the database as.

     password (default: "")
          The password to use when connecting to the database.

     host (default: "")
          The host to make the database connection to.

     port (default: "")
          The port on which to connect to the database.

Mumi
....

Mumi (https://git.savannah.gnu.org/cgit/guix/mumi.git/) is a Web interface to the Debbugs bug tracker, by default for the GNU instance (https://bugs.gnu.org).  Mumi is a Web server, but it also fetches and indexes mail retrieved from Debbugs.

 -- Variable: mumi-service-type
     This is the service type for Mumi.

 -- Data Type: mumi-configuration
     Data type representing the Mumi service configuration.  This type has the following fields:

     mumi (default: mumi)
          The Mumi package to use.

     mailer? (default: #true)
          Whether to enable or disable the mailer component.

     mumi-configuration-sender
          The email address used as the sender for comments.

     mumi-configuration-smtp
          A URI to configure the SMTP settings for Mailutils.  This could be something like sendmail:///path/to/bin/msmtp or any other URI supported by Mailutils.  See SMTP Mailboxes (GNU Mailutils).

FastCGI
.......

FastCGI is an interface between the front-end and the back-end of a web service.  It is a somewhat legacy facility; new web services should generally just talk HTTP between the front-end and the back-end. However there are a number of back-end services such as PHP or the optimized HTTP Git repository access that use FastCGI, so we have support for it in Guix.

To use FastCGI, you configure the front-end web server (e.g., nginx) to dispatch some subset of its requests to the fastcgi backend, which listens on a local TCP or UNIX socket.  There is an intermediary fcgiwrap program that sits between the actual backend process and the web server.  The front-end indicates which backend program to run, passing that information to the fcgiwrap process.

 -- Variable: fcgiwrap-service-type
     A service type for the fcgiwrap FastCGI proxy.

 -- Data Type: fcgiwrap-configuration
     Data type representing the configuration of the fcgiwrap service. This type has the following parameters:

     package (default: fcgiwrap)
          The fcgiwrap package to use.

     socket (default: tcp:127.0.0.1:9000)
          The socket on which the fcgiwrap process should listen, as a string.  Valid SOCKET values include unix:/PATH/TO/UNIX/SOCKET, tcp:DOT.TED.QU.AD:PORT and tcp6:[IPV6_ADDR]:port.

     user (default: fcgiwrap)
     group (default: fcgiwrap)
          The user and group names, as strings, under which to run the fcgiwrap process.  The fastcgi service will ensure that if the user asks for the specific user or group names fcgiwrap that the corresponding user and/or group is present on the system.

          It is possible to configure a FastCGI-backed web service to pass HTTP authentication information from the front-end to the back-end, and to allow fcgiwrap to run the back-end process as a corresponding local user.  To enable this capability on the back-end, run fcgiwrap as the root user and group.  Note that this capability also has to be configured on the front-end as well.

PHP-FPM
.......

PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation with some additional features useful for sites of any size.

These features include:

  * Adaptive process spawning

  * Basic statistics (similar to Apache's mod_status)

  * Advanced process management with graceful stop/start

  * Ability to start workers with different uid/gid/chroot/environment and different php.ini (replaces safe_mode)

  * Stdout & stderr logging

  * Emergency restart in case of accidental opcode cache destruction

  * Accelerated upload support

  * Support for a "slowlog"

  * Enhancements to FastCGI, such as fastcgi_finish_request() - a special function to finish request & flush all data while continuing to do something time-consuming (video converting, stats processing, etc.)

... and much more.

 -- Variable: php-fpm-service-type
     A Service type for php-fpm.

 -- Data Type: php-fpm-configuration
     Data Type for php-fpm service configuration.

     php (default: php)
          The php package to use.

     socket (default: (string-append "/var/run/php" (version-major (package-version php)) "-fpm.sock"))
          The address on which to accept FastCGI requests.  Valid syntaxes are:

          "ip.add.re.ss:port"
               Listen on a TCP socket to a specific address on a specific port.

          "port"
               Listen on a TCP socket to all addresses on a specific port.

          "/path/to/unix/socket"
               Listen on a unix socket.

     user (default: php-fpm)
          User who will own the php worker processes.

     group (default: php-fpm)
          Group of the worker processes.

     socket-user (default: php-fpm)
          User who can speak to the php-fpm socket.

     socket-group (default: nginx)
          Group that can speak to the php-fpm socket.

     pid-file (default: (string-append "/var/run/php" (version-major (package-version php)) "-fpm.pid"))
          The process id of the php-fpm process is written to this file once the service has started.

     log-file (default: (string-append "/var/log/php" (version-major (package-version php)) "-fpm.log"))
          Log for the php-fpm master process.

     process-manager (default: (php-fpm-dynamic-process-manager-configuration))
          Detailed settings for the php-fpm process manager. Must be one of:

          <php-fpm-dynamic-process-manager-configuration>

          <php-fpm-static-process-manager-configuration>

          <php-fpm-on-demand-process-manager-configuration>

     display-errors (default #f)
          Determines whether php errors and warning should be sent to clients and displayed in their browsers. This is useful for local php development, but a security risk for public sites, as error messages can reveal passwords and personal data.

     timezone (default #f)
          Specifies php_admin_value[date.timezone] parameter.

     workers-logfile (default (string-append "/var/log/php" (version-major (package-version php)) "-fpm.www.log"))
          This file will log the stderr outputs of php worker processes. Can be set to #f to disable logging.

     file (default #f)
          An optional override of the whole configuration. You can use the mixed-text-file function or an absolute filepath for it.

     php-ini-file (default #f)
          An optional override of the default php settings. It may be any ``file-like'' object (see file-like objects). You can use the mixed-text-file function or an absolute filepath for it.

          For local development it is useful to set a higher timeout and memory limit for spawned php processes.  This be accomplished with the following operating system configuration snippet:

               (define %local-php-ini
                 (plain-file "php.ini"
                             "memory_limit = 2G
               max_execution_time = 1800"))

               (operating-system
                 ;; ...
                 (services (cons (service php-fpm-service-type
                                          (php-fpm-configuration
                                           (php-ini-file %local-php-ini)))
                                 %base-services)))

          Consult the core php.ini directives (https://www.php.net/manual/en/ini.core.php) for comprehensive documentation on the acceptable php.ini directives.

 -- Data type: php-fpm-dynamic-process-manager-configuration
     Data Type for the dynamic php-fpm process manager.  With the dynamic process manager, spare worker processes are kept around based on its configured limits.

     max-children (default: 5)
          Maximum of worker processes.

     start-servers (default: 2)
          How many worker processes should be started on start-up.

     min-spare-servers (default: 1)
          How many spare worker processes should be kept around at minimum.

     max-spare-servers (default: 3)
          How many spare worker processes should be kept around at maximum.

 -- Data type: php-fpm-static-process-manager-configuration
     Data Type for the static php-fpm process manager.  With the static process manager, an unchanging number of worker processes are created.

     max-children (default: 5)
          Maximum of worker processes.

 -- Data type: php-fpm-on-demand-process-manager-configuration
     Data Type for the on-demand php-fpm process manager.  With the on-demand process manager, worker processes are only created as requests arrive.

     max-children (default: 5)
          Maximum of worker processes.

     process-idle-timeout (default: 10)
          The time in seconds after which a process with no requests is killed.

 -- Procedure: nginx-php-location [#:nginx-package nginx]
     [socket (string-append "/var/run/php"
     (version-major (package-version php)) "-fpm.sock")]
     A helper function to quickly add php to an nginx-server-configuration.

A simple services setup for nginx with php can look like this:

     (services (cons* (service dhcp-client-service-type)
                      (service php-fpm-service-type)
                      (service nginx-service-type
                               (nginx-server-configuration
                                (server-name '("example.com"))
                                (root "/srv/http/")
                                (locations
                                 (list (nginx-php-location)))
                                (listen '("80"))
                                (ssl-certificate #f)
                                (ssl-certificate-key #f)))
                      %base-services))

The cat avatar generator is a simple service to demonstrate the use of php-fpm in Nginx.  It is used to generate cat avatar from a seed, for instance the hash of a user's email address.

 -- Procedure: cat-avatar-generator-service
     [#:cache-dir "/var/cache/cat-avatar-generator"]
     [#:package cat-avatar-generator]
     [#:configuration (nginx-server-configuration)]
     Returns an nginx-server-configuration that inherits configuration.  It extends the nginx configuration to add a server block that serves package, a version of cat-avatar-generator.  During execution, cat-avatar-generator will be able to use cache-dir as its cache directory.

A simple setup for cat-avatar-generator can look like this:

     (services (cons* (cat-avatar-generator-service
                       #:configuration
                       (nginx-server-configuration
                         (server-name '("example.com"))))
                      ...
                      %base-services))

Hpcguix-web
...........

The hpcguix-web (https://github.com/UMCUGenetics/hpcguix-web/) program is a customizable web interface to browse Guix packages, initially designed for users of high-performance computing (HPC) clusters.

 -- Variable: hpcguix-web-service-type
     The service type for hpcguix-web.

 -- Data Type: hpcguix-web-configuration
     Data type for the hpcguix-web service configuration.

     specs (default: #f)
          Either #f or a gexp (see G-Expressions) specifying the hpcguix-web service configuration as an hpcguix-web-configuration record.  The main fields of that record type are:

          title-prefix (default: "hpcguix | ")
               The page title prefix.

          guix-command (default: "guix")
               The guix command to use in examples that appear on HTML pages.

          package-filter-proc (default: (const #t))
               A procedure specifying how to filter packages that are displayed.

          package-page-extension-proc (default: (const '()))
               Extension package for hpcguix-web.

          menu (default: '())
               Additional entry in page menu.

          channels (default: %default-channels)
               List of channels from which the package list is built (see Channels).

          package-list-expiration (default: (* 12 3600))
               The expiration time, in seconds, after which the package list is rebuilt from the latest instances of the given channels.

          See the hpcguix-web repository for a complete example (https://github.com/UMCUGenetics/hpcguix-web/blob/master/hpcweb-configuration.scm).

     package (default: hpcguix-web)
          The hpcguix-web package to use.

     address (default: "127.0.0.1")
          The IP address to listen to.

     port (default: 5000)
          The port number to listen to.

A typical hpcguix-web service declaration looks like this:

     (service hpcguix-web-service-type
              (hpcguix-web-configuration
               (specs
                #~(hpcweb-configuration
                   (title-prefix "Guix-HPC - ")
                   (menu '(("/about" "ABOUT")))))))

     The hpcguix-web service periodically updates the package list it publishes by pulling channels from Git.  To that end, it needs to access X.509 certificates so that it can authenticate Git servers when communicating over HTTPS, and it assumes that /etc/ssl/certs contains those certificates.

     Thus, make sure to add nss-certs or another certificate package to the packages field of your configuration.  X.509 Certificates, for more information on X.509 certificates.

gmnisrv
.......

The gmnisrv (https://git.sr.ht/~sircmpwn/gmnisrv) program is a simple Gemini (https://gemini.circumlunar.space/) protocol server.

 -- Variable: gmnisrv-service-type
     This is the type of the gmnisrv service, whose value should be a gmnisrv-configuration object, as in this example:

          (service gmnisrv-service-type
                   (gmnisrv-configuration
                     (config-file (local-file "./my-gmnisrv.ini"))))

 -- Data Type: gmnisrv-configuration
     Data type representing the configuration of gmnisrv.

     package (default: GMNISRV)
          Package object of the gmnisrv server.

     config-file (default: %default-gmnisrv-config-file)
          File-like object of the gmnisrv configuration file to use.  The default configuration listens on port 1965 and serves files from /srv/gemini.  Certificates are stored in /var/lib/gemini/certs.  For more information, run man gmnisrv and man gmnisrv.ini.

Agate
.....

The Agate (gemini://qwertqwefsday.eu/agate.gmi) (GitHub page over HTTPS (https://github.com/mbrubeck/agate)) program is a simple Gemini (https://gemini.circumlunar.space/) protocol server written in Rust.

 -- Variable: agate-service-type
     This is the type of the agate service, whose value should be an agate-service-type object, as in this example:

          (service agate-service-type
          	 (agate-configuration
          	   (content "/srv/gemini")
          	   (cert "/srv/cert.pem")
          	   (key "/srv/key.rsa")))

     The example above represents the minimal tweaking necessary to get Agate up and running.  Specifying the path to the certificate and key is always necessary, as the Gemini protocol requires TLS by default.

     To obtain a certificate and a key, you could, for example, use OpenSSL, running a command similar to the following example:

          openssl req -x509 -newkey rsa:4096 -keyout key.rsa -out cert.pem \
              -days 3650 -nodes -subj "/CN=example.com"

     Of course, you'll have to replace example.com with your own domain name, and then point the Agate configuration towards the path of the generated key and certificate.

 -- Data Type: agate-configuration
     Data type representing the configuration of Agate.

     package (default: agate)
          The package object of the Agate server.

     content (default: "/srv/gemini")
          The directory from which Agate will serve files.

     cert (default: #f)
          The path to the TLS certificate PEM file to be used for encrypted connections.  Must be filled in with a value from the user.

     key (default: #f)
          The path to the PKCS8 private key file to be used for encrypted connections.  Must be filled in with a value from the user.

     addr (default: '("0.0.0.0:1965" "[::]:1965"))
          A list of the addresses to listen on.

     hostname (default: #f)
          The domain name of this Gemini server.  Optional.

     lang (default: #f)
          RFC 4646 language code(s) for text/gemini documents.  Optional.

     silent? (default: #f)
          Set to #t to disable logging output.

     serve-secret? (default: #f)
          Set to #t to serve secret files (files/directories starting with a dot).

     log-ip? (default: #t)
          Whether or not to output IP addresses when logging.

     user (default: "agate")
          Owner of the agate process.

     group (default: "agate")
          Owner's group of the agate process.

     log-file (default: "/var/log/agate.log")
          The file which should store the logging output of Agate.

Certificate Services
--------------------

The (gnu services certbot) module provides a service to automatically obtain a valid TLS certificate from the Let's Encrypt certificate authority.  These certificates can then be used to serve content securely over HTTPS or other TLS-based protocols, with the knowledge that the client will be able to verify the server's authenticity.

Let's Encrypt (https://letsencrypt.org/) provides the certbot tool to automate the certification process.  This tool first securely generates a key on the server.  It then makes a request to the Let's Encrypt certificate authority (CA) to sign the key.  The CA checks that the request originates from the host in question by using a challenge-response protocol, requiring the server to provide its response over HTTP.  If that protocol completes successfully, the CA signs the key, resulting in a certificate.  That certificate is valid for a limited period of time, and therefore to continue to provide TLS services, the server needs to periodically ask the CA to renew its signature.

The certbot service automates this process: the initial key generation, the initial certification request to the Let's Encrypt service, the web server challenge/response integration, writing the certificate to disk, the automated periodic renewals, and the deployment tasks associated with the renewal (e.g. reloading services, copying keys with different permissions).

Certbot is run twice a day, at a random minute within the hour.  It won't do anything until your certificates are due for renewal or revoked, but running it regularly would give your service a chance of staying online in case a Let's Encrypt-initiated revocation happened for some reason.

By using this service, you agree to the ACME Subscriber Agreement, which can be found there: https://acme-v01.api.letsencrypt.org/directory.

 -- Variable: certbot-service-type
     A service type for the certbot Let's Encrypt client.  Its value must be a certbot-configuration record as in this example:

          (service certbot-service-type
                   (certbot-configuration
                    (email "foo@example.net")
                    (certificates
                     (list
                      (certificate-configuration
                       (domains '("example.net" "www.example.net")))
                      (certificate-configuration
                       (domains '("bar.example.net")))))))

     See below for details about certbot-configuration.

 -- Data Type: certbot-configuration
     Data type representing the configuration of the certbot service. This type has the following parameters:

     package (default: certbot)
          The certbot package to use.

     webroot (default: /var/www)
          The directory from which to serve the Let's Encrypt challenge/response files.

     certificates (default: '())
          A list of certificates-configurations for which to generate certificates and request signatures.  Each certificate has a name and several domains.

     email (default: #f)
          Optional email address used for registration and recovery contact. Setting this is encouraged as it allows you to receive important notifications about the account and issued certificates.

     server (default: #f)
          Optional URL of ACME server.  Setting this overrides certbot's default, which is the Let's Encrypt server.

     rsa-key-size (default: 2048)
          Size of the RSA key.

     default-location (default: see below)
          The default nginx-location-configuration.  Because certbot needs to be able to serve challenges and responses, it needs to be able to run a web server.  It does so by extending the nginx web service with an nginx-server-configuration listening on the DOMAINS on port 80, and which has a nginx-location-configuration for the /.well-known/ URI path subspace used by Let's Encrypt.  See Web Services, for more on these nginx configuration data types.

          Requests to other URL paths will be matched by the default-location, which if present is added to all nginx-server-configurations.

          By default, the default-location will issue a redirect from http://DOMAIN/... to https://DOMAIN/..., leaving you to define what to serve on your site via https.

          Pass #f to not issue a default location.

 -- Data Type: certificate-configuration
     Data type representing the configuration of a certificate. This type has the following parameters:

     name (default: see below)
          This name is used by Certbot for housekeeping and in file paths; it doesn't affect the content of the certificate itself.  To see certificate names, run certbot certificates.

          Its default is the first provided domain.

     domains (default: '())
          The first domain provided will be the subject CN of the certificate, and all domains will be Subject Alternative Names on the certificate.

     challenge (default: #f)
          The challenge type that has to be run by certbot.  If #f is specified, default to the HTTP challenge.  If a value is specified, defaults to the manual plugin (see authentication-hook, cleanup-hook and the documentation at https://certbot.eff.org/docs/using.html#hooks), and gives Let's Encrypt permission to log the public IP address of the requesting machine.

     csr (default: #f)
          File name of Certificate Signing Request (CSR) in DER or PEM format. If #f is specified, this argument will not be passed to certbot. If a value is specified, certbot will use it to obtain a certificate, instead of using a self-generated CSR. The domain-name(s) mentioned in domains, must be consistent with the domain-name(s) mentioned in CSR file.

     authentication-hook (default: #f)
          Command to be run in a shell once for each certificate challenge to be answered.  For this command, the shell variable $CERTBOT_DOMAIN will contain the domain being authenticated, $CERTBOT_VALIDATION contains the validation string and $CERTBOT_TOKEN contains the file name of the resource requested when performing an HTTP-01 challenge.

     cleanup-hook (default: #f)
          Command to be run in a shell once for each certificate challenge that have been answered by the auth-hook.  For this command, the shell variables available in the auth-hook script are still available, and additionally $CERTBOT_AUTH_OUTPUT will contain the standard output of the auth-hook script.

     deploy-hook (default: #f)
          Command to be run in a shell once for each successfully issued certificate.  For this command, the shell variable $RENEWED_LINEAGE will point to the config live subdirectory (for example, "/etc/letsencrypt/live/example.com") containing the new certificates and keys; the shell variable $RENEWED_DOMAINS will contain a space-delimited list of renewed certificate domains (for example, "example.com www.example.com".

     start-self-signed? (default: #t)
          Whether to generate an initial self-signed certificate during system activation.  This option is particularly useful to allow nginx to start before certbot has run, because certbot relies on nginx running to perform HTTP challenges.

For each certificate-configuration, the certificate is saved to /etc/certs/NAME/fullchain.pem and the key is saved to /etc/certs/NAME/privkey.pem.

DNS Services
------------

The (gnu services dns) module provides services related to the domain name system (DNS).  It provides a server service for hosting an authoritative DNS server for multiple zones, slave or master. This service uses Knot DNS (https://www.knot-dns.cz/).  And also a caching and forwarding DNS server for the LAN, which uses dnsmasq (http://www.thekelleys.org.uk/dnsmasq/doc.html).

Knot Service
............

An example configuration of an authoritative server for two zones, one master and one slave, is:

     (define-zone-entries example.org.zone
     ;; Name TTL Class Type Data
       ("@"  ""  "IN"  "A"  "127.0.0.1")
       ("@"  ""  "IN"  "NS" "ns")
       ("ns" ""  "IN"  "A"  "127.0.0.1"))

     (define master-zone
       (knot-zone-configuration
         (domain "example.org")
         (zone (zone-file
                 (origin "example.org")
                 (entries example.org.zone)))))

     (define slave-zone
       (knot-zone-configuration
         (domain "plop.org")
         (dnssec-policy "default")
         (master (list "plop-master"))))

     (define plop-master
       (knot-remote-configuration
         (id "plop-master")
         (address (list "208.76.58.171"))))

     (operating-system
       ;; ...
       (services (cons* (service knot-service-type
                          (knot-configuration
                            (remotes (list plop-master))
                            (zones (list master-zone slave-zone))))
                        ;; ...
                        %base-services)))

 -- Variable: knot-service-type
     This is the type for the Knot DNS server.

     Knot DNS is an authoritative DNS server, meaning that it can serve multiple zones, that is to say domain names you would buy from a registrar.  This server is not a resolver, meaning that it can only resolve names for which it is authoritative.  This server can be configured to serve zones as a master server or a slave server as a per-zone basis.  Slave zones will get their data from masters, and will serve it as an authoritative server.  From the point of view of a resolver, there is no difference between master and slave.

     The following data types are used to configure the Knot DNS server:

 -- Data Type: knot-key-configuration
     Data type representing a key. This type has the following parameters:

     id (default: "")
          An identifier for other configuration fields to refer to this key.  IDs must be unique and must not be empty.

     algorithm (default: #f)
          The algorithm to use.  Choose between #f, 'hmac-md5, 'hmac-sha1, 'hmac-sha224, 'hmac-sha256, 'hmac-sha384 and 'hmac-sha512.

     secret (default: "")
          The secret key itself.

 -- Data Type: knot-acl-configuration
     Data type representing an Access Control List (ACL) configuration. This type has the following parameters:

     id (default: "")
          An identifier for other configuration fields to refer to this key.  IDs must be unique and must not be empty.

     address (default: '())
          An ordered list of IP addresses, network subnets, or network ranges represented with strings.  The query must match one of them.  Empty value means that address match is not required.

     key (default: '())
          An ordered list of references to keys represented with strings.  The string must match a key ID defined in a knot-key-configuration.  No key means that a key is not require to match that ACL.

     action (default: '())
          An ordered list of actions that are permitted or forbidden by this ACL.  Possible values are lists of zero or more elements from 'transfer, 'notify and 'update.

     deny? (default: #f)
          When true, the ACL defines restrictions.  Listed actions are forbidden.  When false, listed actions are allowed.

 -- Data Type: zone-entry
     Data type representing a record entry in a zone file. This type has the following parameters:

     name (default: "@")
          The name of the record.  "@" refers to the origin of the zone.  Names are relative to the origin of the zone.  For example, in the example.org zone, "ns.example.org" actually refers to ns.example.org.example.org. Names ending with a dot are absolute, which means that "ns.example.org." refers to ns.example.org.

     ttl (default: "")
          The Time-To-Live (TTL) of this record.  If not set, the default TTL is used.

     class (default: "IN")
          The class of the record.  Knot currently supports only "IN" and partially "CH".

     type (default: "A")
          The type of the record.  Common types include A (IPv4 address), AAAA (IPv6 address), NS (Name Server) and MX (Mail eXchange).  Many other types are defined.

     data (default: "")
          The data contained in the record.  For instance an IP address associated with an A record, or a domain name associated with an NS record.  Remember that domain names are relative to the origin unless they end with a dot.

 -- Data Type: zone-file
     Data type representing the content of a zone file. This type has the following parameters:

     entries (default: '())
          The list of entries.  The SOA record is taken care of, so you don't need to put it in the list of entries.  This list should probably contain an entry for your primary authoritative DNS server.  Other than using a list of entries directly, you can use define-zone-entries to define a object containing the list of entries more easily, that you can later pass to the entries field of the zone-file.

     origin (default: "")
          The name of your zone.  This parameter cannot be empty.

     ns (default: "ns")
          The domain of your primary authoritative DNS server.  The name is relative to the origin, unless it ends with a dot.  It is mandatory that this primary DNS server corresponds to an NS record in the zone and that it is associated to an IP address in the list of entries.

     mail (default: "hostmaster")
          An email address people can contact you at, as the owner of the zone.  This is translated as <mail>@<origin>.

     serial (default: 1)
          The serial number of the zone.  As this is used to keep track of changes by both slaves and resolvers, it is mandatory that it never decreases. Always increment it when you make a change in your zone.

     refresh (default: (* 2 24 3600))
          The frequency at which slaves will do a zone transfer.  This value is a number of seconds.  It can be computed by multiplications or with (string->duration).

     retry (default: (* 15 60))
          The period after which a slave will retry to contact its master when it fails to do so a first time.

     expiry (default: (* 14 24 3600))
          Default TTL of records.  Existing records are considered correct for at most this amount of time.  After this period, resolvers will invalidate their cache and check again that it still exists.

     nx (default: 3600)
          Default TTL of inexistent records.  This delay is usually short because you want your new domains to reach everyone quickly.

 -- Data Type: knot-remote-configuration
     Data type representing a remote configuration. This type has the following parameters:

     id (default: "")
          An identifier for other configuration fields to refer to this remote.  IDs must be unique and must not be empty.

     address (default: '())
          An ordered list of destination IP addresses.  Addresses are tried in sequence. An optional port can be given with the @ separator.  For instance: (list "1.2.3.4" "2.3.4.5@53").  Default port is 53.

     via (default: '())
          An ordered list of source IP addresses.  An empty list will have Knot choose an appropriate source IP.  An optional port can be given with the @ separator. The default is to choose at random.

     key (default: #f)
          A reference to a key, that is a string containing the identifier of a key defined in a knot-key-configuration field.

 -- Data Type: knot-keystore-configuration
     Data type representing a keystore to hold dnssec keys. This type has the following parameters:

     id (default: "")
          The id of the keystore.  It must not be empty.

     backend (default: 'pem)
          The backend to store the keys in.  Can be 'pem or 'pkcs11.

     config (default: "/var/lib/knot/keys/keys")
          The configuration string of the backend.  An example for the PKCS#11 is: "pkcs11:token=knot;pin-value=1234 /gnu/store/.../lib/pkcs11/libsofthsm2.so". For the pem backend, the string represents a path in the file system.

 -- Data Type: knot-policy-configuration
     Data type representing a dnssec policy.  Knot DNS is able to automatically sign your zones.  It can either generate and manage your keys automatically or use keys that you generate.

     Dnssec is usually implemented using two keys: a Key Signing Key (KSK) that is used to sign the second, and a Zone Signing Key (ZSK) that is used to sign the zone.  In order to be trusted, the KSK needs to be present in the parent zone (usually a top-level domain).  If your registrar supports dnssec, you will have to send them your KSK's hash so they can add a DS record in their zone. This is not automated and need to be done each time you change your KSK.

     The policy also defines the lifetime of keys.  Usually, ZSK can be changed easily and use weaker cryptographic functions (they use lower parameters) in order to sign records quickly, so they are changed often.  The KSK however requires manual interaction with the registrar, so they are changed less often and use stronger parameters because they sign only one record.

     This type has the following parameters:

     id (default: "")
          The id of the policy.  It must not be empty.

     keystore (default: "default")
          A reference to a keystore, that is a string containing the identifier of a keystore defined in a knot-keystore-configuration field.  The "default" identifier means the default keystore (a kasp database that was setup by this service).

     manual? (default: #f)
          Whether the key management is manual or automatic.

     single-type-signing? (default: #f)
          When #t, use the Single-Type Signing Scheme.

     algorithm (default: "ecdsap256sha256")
          An algorithm of signing keys and issued signatures.

     ksk-size (default: 256)
          The length of the KSK.  Note that this value is correct for the default algorithm, but would be unsecure for other algorithms.

     zsk-size (default: 256)
          The length of the ZSK.  Note that this value is correct for the default algorithm, but would be unsecure for other algorithms.

     dnskey-ttl (default: 'default)
          The TTL value for DNSKEY records added into zone apex.  The special 'default value means same as the zone SOA TTL.

     zsk-lifetime (default: (* 30 24 3600))
          The period between ZSK publication and the next rollover initiation.

     propagation-delay (default: (* 24 3600))
          An extra delay added for each key rollover step.  This value should be high enough to cover propagation of data from the master server to all slaves.

     rrsig-lifetime (default: (* 14 24 3600))
          A validity period of newly issued signatures.

     rrsig-refresh (default: (* 7 24 3600))
          A period how long before a signature expiration the signature will be refreshed.

     nsec3? (default: #f)
          When #t, NSEC3 will be used instead of NSEC.

     nsec3-iterations (default: 5)
          The number of additional times the hashing is performed.

     nsec3-salt-length (default: 8)
          The length of a salt field in octets, which is appended to the original owner name before hashing.

     nsec3-salt-lifetime (default: (* 30 24 3600))
          The validity period of newly issued salt field.

 -- Data Type: knot-zone-configuration
     Data type representing a zone served by Knot. This type has the following parameters:

     domain (default: "")
          The domain served by this configuration.  It must not be empty.

     file (default: "")
          The file where this zone is saved.  This parameter is ignored by master zones. Empty means default location that depends on the domain name.

     zone (default: (zone-file))
          The content of the zone file.  This parameter is ignored by slave zones.  It must contain a zone-file record.

     master (default: '())
          A list of master remotes.  When empty, this zone is a master.  When set, this zone is a slave.  This is a list of remotes identifiers.

     ddns-master (default: #f)
          The main master.  When empty, it defaults to the first master in the list of masters.

     notify (default: '())
          A list of slave remote identifiers.

     acl (default: '())
          A list of acl identifiers.

     semantic-checks? (default: #f)
          When set, this adds more semantic checks to the zone.

     zonefile-sync (default: 0)
          The delay between a modification in memory and on disk.  0 means immediate synchronization.

     zonefile-load (default: #f)
          The way the zone file contents are applied during zone load.  Possible values are:

            * #f for using the default value from Knot,

            * 'none for not using the zone file at all,

            * 'difference for computing the difference between already available contents and zone contents and applying it to the current zone contents,

            * 'difference-no-serial for the same as 'difference, but ignoring the SOA serial in the zone file, while the server takes care of it automatically.

            * 'whole for loading zone contents from the zone file.

     journal-content (default: #f)
          The way the journal is used to store zone and its changes.  Possible values are 'none to not use it at all, 'changes to store changes and 'all to store contents.  #f does not set this option, so the default value from Knot is used.

     max-journal-usage (default: #f)
          The maximum size for the journal on disk.  #f does not set this option, so the default value from Knot is used.

     max-journal-depth (default: #f)
          The maximum size of the history.  #f does not set this option, so the default value from Knot is used.

     max-zone-size (default: #f)
          The maximum size of the zone file.  This limit is enforced for incoming transfer and updates.  #f does not set this option, so the default value from Knot is used.

     dnssec-policy (default: #f)
          A reference to a knot-policy-configuration record, or the special name "default".  If the value is #f, there is no dnssec signing on this zone.

     serial-policy (default: 'increment)
          A policy between 'increment and 'unixtime.

 -- Data Type: knot-configuration
     Data type representing the Knot configuration. This type has the following parameters:

     knot (default: knot)
          The Knot package.

     run-directory (default: "/var/run/knot")
          The run directory.  This directory will be used for pid file and sockets.

     includes (default: '())
          A list of strings or file-like objects denoting other files that must be included at the top of the configuration file.

          This can be used to manage secrets out-of-band.  For example, secret keys may be stored in an out-of-band file not managed by Guix, and thus not visible in /gnu/store---e.g., you could store secret key configuration in /etc/knot/secrets.conf and add this file to the includes list.

          One can generate a secret tsig key (for nsupdate and zone transfers with the keymgr command from the knot package.  Note that the package is not automatically installed by the service.  The following example shows how to generate a new tsig key:

               keymgr -t mysecret > /etc/knot/secrets.conf
               chmod 600 /etc/knot/secrets.conf

          Also note that the generated key will be named MYSECRET, so it is the name that needs to be used in the KEY field of the knot-acl-configuration record and in other places that need to refer to that key.

          It can also be used to add configuration not supported by this interface.

     listen-v4 (default: "0.0.0.0")
          An ip address on which to listen.

     listen-v6 (default: "::")
          An ip address on which to listen.

     listen-port (default: 53)
          A port on which to listen.

     keys (default: '())
          The list of knot-key-configuration used by this configuration.

     acls (default: '())
          The list of knot-acl-configuration used by this configuration.

     remotes (default: '())
          The list of knot-remote-configuration used by this configuration.

     zones (default: '())
          The list of knot-zone-configuration used by this configuration.

Knot Resolver Service
.....................

 -- Variable: knot-resolver-service-type
     This is the type of the knot resolver service, whose value should be a knot-resolver-configuration object as in this example:

          (service knot-resolver-service-type
                   (knot-resolver-configuration
                     (kresd-config-file (plain-file "kresd.conf" "
          net.listen('192.168.0.1', 5353)
          user('knot-resolver', 'knot-resolver')
          modules = { 'hints > iterate', 'stats', 'predict' }
          cache.size = 100 * MB
          "))))

     For more information, refer its manual (https://knot-resolver.readthedocs.io/en/stable/config-overview.html).

 -- Data Type: knot-resolver-configuration
     Data type representing the configuration of knot-resolver.

     package (default: KNOT-RESOLVER)
          Package object of the knot DNS resolver.

     kresd-config-file (default: %kresd.conf)
          File-like object of the kresd configuration file to use, by default it will listen on 127.0.0.1 and ::1.

     garbage-collection-interval (default: 1000)
          Number of milliseconds for kres-cache-gc to periodically trim the cache.

Dnsmasq Service
...............

 -- Variable: dnsmasq-service-type
     This is the type of the dnsmasq service, whose value should be a dnsmasq-configuration object as in this example:

          (service dnsmasq-service-type
                   (dnsmasq-configuration
                     (no-resolv? #t)
                     (servers '("192.168.1.1"))))

 -- Data Type: dnsmasq-configuration
     Data type representing the configuration of dnsmasq.

     package (default: DNSMASQ)
          Package object of the dnsmasq server.

     no-hosts? (default: #f)
          When true, don't read the hostnames in /etc/hosts.

     port (default: 53)
          The port to listen on.  Setting this to zero completely disables DNS responses, leaving only DHCP and/or TFTP functions.

     local-service? (default: #t)
          Accept DNS queries only from hosts whose address is on a local subnet, ie a subnet for which an interface exists on the server.

     listen-addresses (default: '())
          Listen on the given IP addresses.

     resolv-file (default: "/etc/resolv.conf")
          The file to read the IP address of the upstream nameservers from.

     no-resolv? (default: #f)
          When true, don't read RESOLV-FILE.

     forward-private-reverse-lookup? (default: #t)
          When false, all reverse lookups for private IP ranges are answered with "no such domain" rather than being forwarded upstream.

     query-servers-in-order? (default: #f)
          When true, dnsmasq queries the servers in the same order as they appear in SERVERS.

     servers (default: '())
          Specify IP address of upstream servers directly.

     servers-file (default: #f)
          Specify file containing upstream servers. This file is re-read when dnsmasq receives SIGHUP. Could be either a string or a file-like object.

     addresses (default: '())
          For each entry, specify an IP address to return for any host in the given domains.  Queries in the domains are never forwarded and always replied to with the specified IP address.

          This is useful for redirecting hosts locally, for example:

               (service dnsmasq-service-type
                        (dnsmasq-configuration
                          (addresses
                            '(; Redirect to a local web-server.
                              "/example.org/127.0.0.1"
                              ; Redirect subdomain to a specific IP.
                              "/subdomain.example.org/192.168.1.42"))))

          Note that rules in /etc/hosts take precedence over this.

     cache-size (default: 150)
          Set the size of dnsmasq's cache.  Setting the cache size to zero disables caching.

     negative-cache? (default: #t)
          When false, disable negative caching.

     cpe-id (default: #f)
          If set, add a CPE (Customer-Premises Equipment) identifier to DNS queries which are forwarded upstream.

     tftp-enable? (default: #f)
          Whether to enable the built-in TFTP server.

     tftp-no-fail? (default: #f)
          If true, does not fail dnsmasq if the TFTP server could not start up.

     tftp-single-port? (default: #f)
          Whether to use only one single port for TFTP.

     tftp-secure? (default: #f)
          If true, only files owned by the user running the dnsmasq process are accessible.

          If dnsmasq is being run as root, different rules apply: tftp-secure? has no effect, but only files which have the world-readable bit set are accessible.

     tftp-max (default: #f)
          If set, sets the maximal number of concurrent connections allowed.

     tftp-mtu (default: #f)
          If set, sets the MTU for TFTP packets to that value.

     tftp-no-blocksize? (default: #f)
          If true, stops the TFTP server from negotiating the blocksize with a client.

     tftp-lowercase? (default: #f)
          Whether to convert all filenames in TFTP requests to lowercase.

     tftp-port-range (default: #f)
          If set, fixes the dynamical ports (one per client) to the given range ("<start>,<end>").

     tftp-root (default: /var/empty,lo)
          Look for files to transfer using TFTP relative to the given directory. When this is set, TFTP paths which include .. are rejected, to stop clients getting outside the specified root.  Absolute paths (starting with /) are allowed, but they must be within the TFTP-root.  If the optional interface argument is given, the directory is only used for TFTP requests via that interface.

     tftp-unique-root (default: #f)
          If set, add the IP or hardware address of the TFTP client as a path component on the end of the TFTP-root.  Only valid if a TFTP root is set and the directory exists.  Defaults to adding IP address (in standard dotted-quad format).

          For instance, if --tftp-root is /tftp and client 1.2.3.4 requests file myfile then the effective path will be /tftp/1.2.3.4/myfile if /tftp/1.2.3.4 exists or /tftp/myfile otherwise.  When =mac is specified it will append the MAC address instead, using lowercase zero padded digits separated by dashes, e.g.: 01-02-03-04-aa-bb.  Note that resolving MAC addresses is only possible if the client is in the local network or obtained a DHCP lease from dnsmasq.

VNC Services
------------

The (gnu services vnc) module provides services related to Virtual Network Computing (VNC), which makes it possible to locally use graphical Xorg applications running on a remote machine. Combined with a graphical manager that supports the X Display Manager Control Protocol, such as GDM (see gdm) or LightDM (see lightdm), it is possible to remote an entire desktop for a multi-user environment.

Xvnc
....

Xvnc is a VNC server that spawns its own X window server; which means it can run on headless servers.  The Xvnc implementations provided by the tigervnc-server and turbovnc aim to be fast and efficient.

 -- Variable: xvnc-service-type

     The xvnc-service-type service can be configured via the xvnc-configuration record, documented below.  A second virtual display could be made available on a remote machine via the following configuration:

     (service xvnc-service-type
              (xvnc-configuration (display-number 10)))

As a demonstration, the xclock command could then be started on the remote machine on display number 10, and it could be displayed locally via the vncviewer command:

     # Start xclock on the remote machine.
     ssh -L5910:localhost:5910 YOUR-HOST -- guix shell xclock \
         -- env DISPLAY=:10 xclock
     # Access it via VNC.
     guix shell tigervnc-client -- vncviewer localhost:5910

The following configuration combines XDMCP and Inetd to allow multiple users to concurrently use the remote system and login graphically via the GDM display manager:

     (operating-system
       [...]
       (services (cons*
                  [...]
                  (service xvnc-service-type (xvnc-configuration
                                              (display-number 5)
                                              (localhost? #f)
                                              (xdmcp? #t)
                                              (inetd? #t)))
                  (modify-services %desktop-services
                    (gdm-service-type config => (gdm-configuration
                                                 (inherit config)
                                                 (auto-suspend? #f)
                                                 (xdmcp? #t)))))))

A remote user could then connect to it by using the vncviewer command or a compatible VNC client and start a desktop session of their choosing:

     vncviewer remote-host:5905

     Unless your machine is in a controlled environment, for security reasons, the localhost? configuration of the xvnc-configuration record should be left to its default #t value and exposed via a secure means such as an SSH port forward.  The XDMCP port, UDP 177 should also be blocked from the outside by a firewall, as it is not a secure protocol and can expose login credentials in clear.

 -- Data Type: xvnc-configuration
     Available xvnc-configuration fields are:

     xvnc (default: tigervnc-server) (type: file-like)
          The package that provides the Xvnc binary.

     display-number (default: 0) (type: number)
          The display number used by Xvnc.  You should set this to a number not already used a Xorg server.

     geometry (default: "1024x768") (type: string)
          The size of the desktop to be created.

     depth (default: 24) (type: color-depth)
          The pixel depth in bits of the desktop to be created.  Accepted values are 16, 24 or 32.

     port (type: maybe-port)
          The port on which to listen for connections from viewers.  When left unspecified, it defaults to 5900 plus the display number.

     ipv4? (default: #t) (type: boolean)
          Use IPv4 for incoming and outgoing connections.

     ipv6? (default: #t) (type: boolean)
          Use IPv6 for incoming and outgoing connections.

     password-file (type: maybe-string)
          The password file to use, if any.  Refer to vncpasswd(1) to learn how to generate such a file.

     xdmcp? (default: #f) (type: boolean)
          Query the XDMCP server for a session.  This enables users to log in a desktop session from the login manager screen.  For a multiple users scenario, you'll want to enable the inetd? option as well, so that each connection to the VNC server is handled separately rather than shared.

     inetd? (default: #f) (type: boolean)
          Use an Inetd-style service, which runs the Xvnc server on demand.

     frame-rate (default: 60) (type: number)
          The maximum number of updates per second sent to each client.

     security-types (default: '("None")) (type: security-types)
          The allowed security schemes to use for incoming connections.  The default is "None", which is safe given that Xvnc is configured to authenticate the user via the display manager, and only for local connections.  Accepted values are any of the following: ("None" "VncAuth" "Plain" "TLSNone" "TLSVnc" "TLSPlain" "X509None" "X509Vnc")

     localhost? (default: #t) (type: boolean)
          Only allow connections from the same machine.  It is set to #true by default for security, which means SSH or another secure means should be used to expose the remote port.

     log-level (default: 30) (type: log-level)
          The log level, a number between 0 and 100, 100 meaning most verbose output.  The log messages are output to syslog.

     extra-options (default: '()) (type: strings)
          This can be used to provide extra Xvnc options not exposed via this <xvnc-configuration> record.

VPN Services
------------

The (gnu services vpn) module provides services related to virtual private networks (VPNs).

Bitmask
.......

 -- Variable: bitmask-service-type
     A service type for the Bitmask (https://bitmask.net) VPN client.  It makes the client available in the system and loads its polkit policy.  Please note that the client expects an active polkit-agent, which is either run by your desktop-environment or should be run manually.

OpenVPN
.......

It provides a client service for your machine to connect to a VPN, and a server service for your machine to host a VPN. Both openvpn-client-service-type and openvpn-server-service-type can be run simultaneously.

 -- Variable: openvpn-client-service-type
     Type of the service that runs openvpn, a VPN daemon, as a client.

     The value for this service is a <openvpn-client-configuration> object.

 -- Variable: openvpn-server-service-type
     Type of the service that runs openvpn, a VPN daemon, as a server.

     The value for this service is a <openvpn-server-configuration> object.

 -- Data Type: openvpn-client-configuration
     Available openvpn-client-configuration fields are:

     openvpn (default: openvpn) (type: file-like)
          The OpenVPN package.

     pid-file (default: "/var/run/openvpn/openvpn.pid") (type: string)
          The OpenVPN pid file.

     proto (default: udp) (type: proto)
          The protocol (UDP or TCP) used to open a channel between clients and servers.

     dev (default: tun) (type: dev)
          The device type used to represent the VPN connection.

     ca (default: "/etc/openvpn/ca.crt") (type: maybe-string)
          The certificate authority to check connections against.

     cert (default: "/etc/openvpn/client.crt") (type: maybe-string)
          The certificate of the machine the daemon is running on.  It should be signed by the authority given in ca.

     key (default: "/etc/openvpn/client.key") (type: maybe-string)
          The key of the machine the daemon is running on.  It must be the key whose certificate is cert.

     comp-lzo? (default: #t) (type: boolean)
          Whether to use the lzo compression algorithm.

     persist-key? (default: #t) (type: boolean)
          Don't re-read key files across SIGUSR1 or --ping-restart.

     persist-tun? (default: #t) (type: boolean)
          Don't close and reopen TUN/TAP device or run up/down scripts across SIGUSR1 or --ping-restart restarts.

     fast-io? (default: #f) (type: boolean)
          (Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to poll/epoll/select prior to the write operation.

     verbosity (default: 3) (type: number)
          Verbosity level.

     tls-auth (default: #f) (type: tls-auth-client)
          Add an additional layer of HMAC authentication on top of the TLS control channel to protect against DoS attacks.

     auth-user-pass (type: maybe-string)
          Authenticate with server using username/password.  The option is a file containing username/password on 2 lines.  Do not use a file-like object as it would be added to the store and readable by any user.

     verify-key-usage? (default: #t) (type: key-usage)
          Whether to check the server certificate has server usage extension.

     bind? (default: #f) (type: bind)
          Bind to a specific local port number.

     resolv-retry? (default: #t) (type: resolv-retry)
          Retry resolving server address.

     remote (default: '()) (type: openvpn-remote-list)
          A list of remote servers to connect to.

           -- Data Type: openvpn-remote-configuration
               Available openvpn-remote-configuration fields are:

               name (default: "my-server") (type: string)
                    Server name.

               port (default: 1194) (type: number)
                    Port number the server listens to.

 -- Data Type: openvpn-server-configuration
     Available openvpn-server-configuration fields are:

     openvpn (default: openvpn) (type: file-like)
          The OpenVPN package.

     pid-file (default: "/var/run/openvpn/openvpn.pid") (type: string)
          The OpenVPN pid file.

     proto (default: udp) (type: proto)
          The protocol (UDP or TCP) used to open a channel between clients and servers.

     dev (default: tun) (type: dev)
          The device type used to represent the VPN connection.

     ca (default: "/etc/openvpn/ca.crt") (type: maybe-string)
          The certificate authority to check connections against.

     cert (default: "/etc/openvpn/client.crt") (type: maybe-string)
          The certificate of the machine the daemon is running on.  It should be signed by the authority given in ca.

     key (default: "/etc/openvpn/client.key") (type: maybe-string)
          The key of the machine the daemon is running on.  It must be the key whose certificate is cert.

     comp-lzo? (default: #t) (type: boolean)
          Whether to use the lzo compression algorithm.

     persist-key? (default: #t) (type: boolean)
          Don't re-read key files across SIGUSR1 or --ping-restart.

     persist-tun? (default: #t) (type: boolean)
          Don't close and reopen TUN/TAP device or run up/down scripts across SIGUSR1 or --ping-restart restarts.

     fast-io? (default: #f) (type: boolean)
          (Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to poll/epoll/select prior to the write operation.

     verbosity (default: 3) (type: number)
          Verbosity level.

     tls-auth (default: #f) (type: tls-auth-server)
          Add an additional layer of HMAC authentication on top of the TLS control channel to protect against DoS attacks.

     port (default: 1194) (type: number)
          Specifies the port number on which the server listens.

     server (default: "10.8.0.0 255.255.255.0") (type: ip-mask)
          An ip and mask specifying the subnet inside the virtual network.

     server-ipv6 (default: #f) (type: cidr6)
          A CIDR notation specifying the IPv6 subnet inside the virtual network.

     dh (default: "/etc/openvpn/dh2048.pem") (type: string)
          The Diffie-Hellman parameters file.

     ifconfig-pool-persist (default: "/etc/openvpn/ipp.txt") (type: string)
          The file that records client IPs.

     redirect-gateway? (default: #f) (type: gateway)
          When true, the server will act as a gateway for its clients.

     client-to-client? (default: #f) (type: boolean)
          When true, clients are allowed to talk to each other inside the VPN.

     keepalive (default: (10 120)) (type: keepalive)
          Causes ping-like messages to be sent back and forth over the link so that each side knows when the other side has gone down.  keepalive requires a pair.  The first element is the period of the ping sending, and the second element is the timeout before considering the other side down.

     max-clients (default: 100) (type: number)
          The maximum number of clients.

     status (default: "/var/run/openvpn/status") (type: string)
          The status file.  This file shows a small report on current connection. It is truncated and rewritten every minute.

     client-config-dir (default: '()) (type: openvpn-ccd-list)
          The list of configuration for some clients.

strongSwan
----------

Currently, the strongSwan service only provides legacy-style configuration with ipsec.conf and ipsec.secrets files.

 -- Variable: strongswan-service-type
     A service type for configuring strongSwan for IPsec VPN (Virtual Private Networking).  Its value must be a strongswan-configuration record as in this example:

          (service strongswan-service-type
                   (strongswan-configuration
                    (ipsec-conf "/etc/ipsec.conf")
                    (ipsec-secrets "/etc/ipsec.secrets")))

 -- Data Type: strongswan-configuration
     Data type representing the configuration of the StrongSwan service.

     strongswan
          The strongSwan package to use for this service.

     ipsec-conf (default: #f)
          The file name of your ipsec.conf.  If not #f, then this and ipsec-secrets must both be strings.

     ipsec-secrets (default #f)
          The file name of your ipsec.secrets.  If not #f, then this and ipsec-conf must both be strings.

Wireguard
.........

 -- Variable: wireguard-service-type
     A service type for a Wireguard tunnel interface.  Its value must be a wireguard-configuration record as in this example:

          (service wireguard-service-type
                   (wireguard-configuration
                    (peers
                     (list
                      (wireguard-peer
                       (name "my-peer")
                       (endpoint "my.wireguard.com:51820")
                       (public-key "hzpKg9X1yqu1axN6iJp0mWf6BZGo8m1wteKwtTmDGF4=")
                       (allowed-ips '("10.0.0.2/32")))))))

 -- Data Type: wireguard-configuration
     Data type representing the configuration of the Wireguard service.

     wireguard
          The wireguard package to use for this service.

     interface (default: "wg0")
          The interface name for the VPN.

     addresses (default: '("10.0.0.1/32"))
          The IP addresses to be assigned to the above interface.

     port (default: 51820)
          The port on which to listen for incoming connections.

     dns (default: '()))
          The DNS server(s) to announce to VPN clients via DHCP.

     monitor-ips? (default: #f)
          Whether to monitor the resolved Internet addresses (IPs) of the endpoints of the configured peers, resetting the peer endpoints using an IP address that no longer correspond to their freshly resolved host name.  Set this to #t if one or more endpoints use host names provided by a dynamic DNS service to keep the sessions alive.

     monitor-ips-interval (default: '(next-minute (range 0 60 5)))
          The time interval at which the IP monitoring job should run, provided as an mcron time specification (see Guile Syntax (mcron)).

     private-key (default: "/etc/wireguard/private.key")
          The private key file for the interface.  It is automatically generated if the file does not exist.

     peers (default: '())
          The authorized peers on this interface.  This is a list of WIREGUARD-PEER records.

     pre-up (default: '())
          The script commands to be run before setting up the interface.

     post-up (default: '())
          The script commands to be run after setting up the interface.

     pre-down (default: '())
          The script commands to be run before tearing down the interface.

     post-down (default: '())
          The script commands to be run after tearing down the interface.

     table (default: "auto")
          The routing table to which routes are added, as a string.  There are two special values: "off" that disables the creation of routes altogether, and "auto" (the default) that adds routes to the default table and enables special handling of default routes.

 -- Data Type: wireguard-peer
     Data type representing a Wireguard peer attached to a given interface.

     name
          The peer name.

     endpoint (default: #f)
          The optional endpoint for the peer, such as "demo.wireguard.com:51820".

     public-key
          The peer public-key represented as a base64 string.

     preshared-key (default: #f)
          An optional pre-shared key file for this peer.  The given file will not be autogenerated.

     allowed-ips
          A list of IP addresses from which incoming traffic for this peer is allowed and to which incoming traffic for this peer is directed.

     keep-alive (default: #f)
          An optional time interval in seconds.  A packet will be sent to the server endpoint once per time interval.  This helps receiving incoming connections from this peer when you are behind a NAT or a firewall.

Network File System
-------------------

The (gnu services nfs) module provides the following services, which are most commonly used in relation to mounting or exporting directory trees as network file systems (NFS).

While it is possible to use the individual components that together make up a Network File System service, we recommended to configure an NFS server with the nfs-service-type.

NFS Service
...........

The NFS service takes care of setting up all NFS component services, kernel configuration file systems, and installs configuration files in the locations that NFS expects.

 -- Variable: nfs-service-type
     A service type for a complete NFS server.

 -- Data Type: nfs-configuration
     This data type represents the configuration of the NFS service and all of its subsystems.

     It has the following parameters:

     nfs-utils (default: nfs-utils)
          The nfs-utils package to use.

     nfs-versions (default: '("4.2" "4.1" "4.0"))
          If a list of string values is provided, the rpc.nfsd daemon will be limited to supporting the given versions of the NFS protocol.

     exports (default: '())
          This is a list of directories the NFS server should export.  Each entry is a list consisting of two elements: a directory name and a string containing all options.  This is an example in which the directory /export is served to all NFS clients as a read-only share:

               (nfs-configuration
                (exports
                 '(("/export"
                    "*(ro,insecure,no_subtree_check,crossmnt,fsid=0)"))))

     rpcmountd-port (default: #f)
          The network port that the rpc.mountd daemon should use.

     rpcstatd-port (default: #f)
          The network port that the rpc.statd daemon should use.

     rpcbind (default: rpcbind)
          The rpcbind package to use.

     idmap-domain (default: "localdomain")
          The local NFSv4 domain name.

     nfsd-port (default: 2049)
          The network port that the nfsd daemon should use.

     nfsd-threads (default: 8)
          The number of threads used by the nfsd daemon.

     nfsd-tcp? (default: #t)
          Whether the nfsd daemon should listen on a TCP socket.

     nfsd-udp? (default: #f)
          Whether the nfsd daemon should listen on a UDP socket.

     pipefs-directory (default: "/var/lib/nfs/rpc_pipefs")
          The directory where the pipefs file system is mounted.

     debug (default: '()")
          A list of subsystems for which debugging output should be enabled.  This is a list of symbols.  Any of these symbols are valid: nfsd, nfs, rpc, idmap, statd, or mountd.

If you don't need a complete NFS service or prefer to build it yourself you can use the individual component services that are documented below.

RPC Bind Service
................

The RPC Bind service provides a facility to map program numbers into universal addresses. Many NFS related services use this facility.  Hence it is automatically started when a dependent service starts.

 -- Variable: rpcbind-service-type
     A service type  for the RPC portmapper daemon.

 -- Data Type: rpcbind-configuration
     Data type representing the configuration of the RPC Bind Service. This type has the following parameters:

     rpcbind (default: rpcbind)
          The rpcbind package to use.

     warm-start? (default: #t)
          If this parameter is #t, then the daemon will read a state file on startup thus reloading state information saved by a previous instance.

Pipefs Pseudo File System
.........................

The pipefs file system is used to transfer NFS related data between the kernel and user space programs.

 -- Variable: pipefs-service-type
     A service type for the pipefs pseudo file system.

 -- Data Type: pipefs-configuration
     Data type representing the configuration of the pipefs pseudo file system service. This type has the following parameters:

     mount-point (default: "/var/lib/nfs/rpc_pipefs")
          The directory to which the file system is to be attached.

GSS Daemon Service
..................

The global security system (GSS) daemon provides strong security for RPC based protocols. Before exchanging RPC requests an RPC client must establish a security context.  Typically this is done using the Kerberos command kinit or automatically at login time using PAM services (see Kerberos Services).

 -- Variable: gss-service-type
     A service type for the Global Security System (GSS) daemon.

 -- Data Type: gss-configuration
     Data type representing the configuration of the GSS daemon service. This type has the following parameters:

     nfs-utils (default: nfs-utils)
          The package in which the rpc.gssd command is to be found.

     pipefs-directory (default: "/var/lib/nfs/rpc_pipefs")
          The directory where the pipefs file system is mounted.

IDMAP Daemon Service
....................

The idmap daemon service provides mapping between user IDs and user names. Typically it is required in order to access file systems mounted via NFSv4.

 -- Variable: idmap-service-type
     A service type for the Identity Mapper (IDMAP) daemon.

 -- Data Type: idmap-configuration
     Data type representing the configuration of the IDMAP daemon service. This type has the following parameters:

     nfs-utils (default: nfs-utils)
          The package in which the rpc.idmapd command is to be found.

     pipefs-directory (default: "/var/lib/nfs/rpc_pipefs")
          The directory where the pipefs file system is mounted.

     domain (default: #f)
          The local NFSv4 domain name. This must be a string or #f. If it is #f then the daemon will use the host's fully qualified domain name.

     verbosity (default: 0)
          The verbosity level of the daemon.

Samba Services
--------------

The (gnu services samba) module provides service definitions for Samba as well as additional helper services.  Currently it provides the following services.

Samba
.....

Samba (https://www.samba.org) provides network shares for folders and printers using the SMB/CIFS protocol commonly used on Windows.  It can also act as an Active Directory Domain Controller (AD DC) for other hosts in an heterougenious network with different types of Computer systems.

 -- Variable: samba-service-type

     The service type to enable the samba services samba, nmbd, smbd and winbindd.  By default this service type does not run any of the Samba daemons; they must be enabled individually.

     Below is a basic example that configures a simple, anonymous (unauthenticated) Samba file share exposing the /public directory.

          The /public directory and its contents must be world readable/writable, so you'll want to run chmod -R 777 /public on it.

          Such a Samba configuration should only be used in controlled environments, and you should not share any private files using it, as anyone connecting to your network would be able to access them.

          (service samba-service-type (samba-configuration
                                       (enable-smbd? #t)
                                       (config-file (plain-file "smb.conf" "\
          [global]
          map to guest = Bad User
          logging = syslog@1

          [public]
          browsable = yes
          path = /public
          read only = no
          guest ok = yes
          guest only = yes\n"))))

 -- Data Type: samba-service-configuration
     Configuration record for the Samba suite.

     package (default: samba)
          The samba package to use.

     config-file (default: #f)
          The config file to use.  To learn about its syntax, run man smb.conf.

     enable-samba? (default: #f)
          Enable the samba daemon.

     enable-smbd? (default: #f)
          Enable the smbd daemon.

     enable-nmbd? (default: #f)
          Enable the nmbd daemon.

     enable-winbindd? (default: #f)
          Enable the winbindd daemon.

Web Service Discovery Daemon
............................

The WSDD (Web Service Discovery daemon) implements the Web Services Dynamic Discovery (http://docs.oasis-open.org/ws-dd/discovery/1.1/os/wsdd-discovery-1.1-spec-os.html) protocol that enables host discovery over Multicast DNS, similar to what Avahi does.  It is a drop-in replacement for SMB hosts that have had SMBv1 disabled for security reasons.

 -- Variable: wsdd-service-type
     Service type for the WSD host daemon.  The value for this service type is a wsdd-configuration record.  The details for the wsdd-configuration record type are given below.

 -- Data Type: wsdd-configuration
     This data type represents the configuration for the wsdd service.

     package (default: wsdd)
          The wsdd package to use.

     ipv4only? (default: #f)
          Only listen to IPv4 addresses.

     ipv6only (default: #f)
          Only listen to IPv6 addresses.  Please note: Activating both options is not possible, since there would be no IP versions to listen to.

     chroot (default: #f)
          Chroot into a separate directory to prevent access to other directories. This is to increase security in case there is a vulnerability in wsdd.

     hop-limit (default: 1)
          Limit to the level of hops for multicast packets.  The default is 1 which should prevent packets from leaving the local network.

     interface (default: '())
          Limit to the given list of interfaces to listen to.  By default wsdd will listen to all interfaces.  Except the loopback interface is never used.

     uuid-device (default: #f)
          The WSD protocol requires a device to have a UUID.  Set this to manually assign the service a UUID.

     domain (default: #f)
          Notify this host is a member of an Active Directory.

     host-name (default: #f)
          Manually set the hostname rather than letting wsdd inherit this host's hostname.  Only the host name part of a possible FQDN will be used in the default case.

     preserve-case? (default: #f)
          By default wsdd will convert the hostname in workgroup to all uppercase.  The opposite is true for hostnames in domains.  Setting this parameter will preserve case.

     workgroup (default: "WORKGROUP")
          Change the name of the workgroup.  By default wsdd reports this host being member of a workgroup.

Continuous Integration
----------------------

Cuirass (https://guix.gnu.org/cuirass/) is a continuous integration tool for Guix.  It can be used both for development and for providing substitutes to others (see Substitutes).

The (gnu services cuirass) module provides the following service.

 -- Procedure: cuirass-service-type
     The type of the Cuirass service.  Its value must be a cuirass-configuration object, as described below.

To add build jobs, you have to set the specifications field of the configuration.  For instance, the following example will build all the packages provided by the my-channel channel.

     (define %cuirass-specs
       #~(list (specification
                (name "my-channel")
                (build '(channels my-channel))
                (channels
                 (cons (channel
                        (name 'my-channel)
                        (url "https://my-channel.git"))
                       %default-channels)))))

     (service cuirass-service-type
              (cuirass-configuration
               (specifications %cuirass-specs)))

To build the linux-libre package defined by the default Guix channel, one can use the following configuration.

     (define %cuirass-specs
       #~(list (specification
                (name "my-linux")
                (build '(packages "linux-libre")))))

     (service cuirass-service-type
              (cuirass-configuration
               (specifications %cuirass-specs)))

The other configuration possibilities, as well as the specification record itself are described in the Cuirass manual (see Specifications (Cuirass)).

While information related to build jobs is located directly in the specifications, global settings for the cuirass process are accessible in other cuirass-configuration fields.

 -- Data Type: cuirass-configuration
     Data type representing the configuration of Cuirass.

     cuirass (default: cuirass)
          The Cuirass package to use.

     log-file (default: "/var/log/cuirass.log")
          Location of the log file.

     web-log-file (default: "/var/log/cuirass-web.log")
          Location of the log file used by the web interface.

     cache-directory (default: "/var/cache/cuirass")
          Location of the repository cache.

     user (default: "cuirass")
          Owner of the cuirass process.

     group (default: "cuirass")
          Owner's group of the cuirass process.

     interval (default: 60)
          Number of seconds between the poll of the repositories followed by the Cuirass jobs.

     parameters (default: #f)
          Read parameters from the given PARAMETERS file.  The supported parameters are described here (see Parameters (Cuirass)).

     remote-server (default: #f)
          A cuirass-remote-server-configuration record to use the build remote mechanism or #f to use the default build mechanism.

     database (default: "dbname=cuirass host=/var/run/postgresql")
          Use DATABASE as the database containing the jobs and the past build results. Since Cuirass uses PostgreSQL as a database engine, DATABASE must be a string such as "dbname=cuirass host=localhost".

     port (default: 8081)
          Port number used by the HTTP server.

     host (default: "localhost")
          Listen on the network interface for HOST.  The default is to accept connections from localhost.

     specifications (default: #~'())
          A gexp (see G-Expressions) that evaluates to a list of specifications records.  The specification record is described in the Cuirass manual (see Specifications (Cuirass)).

     use-substitutes? (default: #f)
          This allows using substitutes to avoid building every dependencies of a job from source.

     one-shot? (default: #f)
          Only evaluate specifications and build derivations once.

     fallback? (default: #f)
          When substituting a pre-built binary fails, fall back to building packages locally.

     extra-options (default: '())
          Extra options to pass when running the Cuirass processes.

Cuirass remote building
.......................

Cuirass supports two mechanisms to build derivations.

  * Using the local Guix daemon. This is the default build mechanism.  Once the build jobs are evaluated, they are sent to the local Guix daemon.  Cuirass then listens to the Guix daemon output to detect the various build events.

  * Using the remote build mechanism. The build jobs are not submitted to the local Guix daemon.  Instead, a remote server dispatches build requests to the connect remote workers, according to the build priorities.

To enable this build mode a cuirass-remote-server-configuration record must be passed as remote-server argument of the cuirass-configuration record.  The cuirass-remote-server-configuration record is described below.

This build mode scales way better than the default build mode.  This is the build mode that is used on the GNU Guix build farm at https://ci.guix.gnu.org.  It should be preferred when using Cuirass to build large amount of packages.

 -- Data Type: cuirass-remote-server-configuration
     Data type representing the configuration of the Cuirass remote-server.

     backend-port (default: 5555)
          The TCP port for communicating with remote-worker processes using ZMQ.  It defaults to 5555.

     log-port (default: 5556)
          The TCP port of the log server.  It defaults to 5556.

     publish-port (default: 5557)
          The TCP port of the publish server.  It defaults to 5557.

     log-file (default: "/var/log/cuirass-remote-server.log")
          Location of the log file.

     cache (default: "/var/cache/cuirass/remote")
          Use CACHE directory to cache build log files.

     log-expiry (default: 6 months)
          The duration in seconds after which build logs collected by cuirass remote-worker may be deleted.

     trigger-url (default: #f)
          Once a substitute is successfully fetched, trigger substitute baking at TRIGGER-URL.

     publish? (default: #t)
          If set to false, do not start a publish server and ignore the publish-port argument.  This can be useful if there is already a standalone publish server standing next to the remote server.

     public-key

     private-key
          Use the specific FILEs as the public/private key pair used to sign the store items being published.

At least one remote worker must also be started on any machine of the local network to actually perform the builds and report their status.

 -- Data Type: cuirass-remote-worker-configuration
     Data type representing the configuration of the Cuirass remote-worker.

     cuirass (default: cuirass)
          The Cuirass package to use.

     workers (default: 1)
          Start WORKERS parallel workers.

     server (default: #f)
          Do not use Avahi discovery and connect to the given server IP address instead.

     systems (default: (list (%current-system)))
          Only request builds for the given SYSTEMS.

     log-file (default: "/var/log/cuirass-remote-worker.log")
          Location of the log file.

     publish-port (default: 5558)
          The TCP port of the publish server.  It defaults to 5558.

     substitute-urls (default: %default-substitute-urls)
          The list of URLs where to look for substitutes by default.

     public-key

     private-key
          Use the specific FILEs as the public/private key pair used to sign the store items being published.

Laminar
.......

Laminar (https://laminar.ohwg.net/) is a lightweight and modular Continuous Integration service.  It doesn't have a configuration web UI instead uses version-controllable configuration files and scripts.

Laminar encourages the use of existing tools such as bash and cron instead of reinventing them.

 -- Variable: laminar-service-type
     The type of the Laminar service.  Its value must be a laminar-configuration object, as described below.

     All configuration values have defaults, a minimal configuration to get Laminar running is shown below. By default, the web interface is available on port 8080.

          (service laminar-service-type)

 -- Data Type: laminar-configuration
     Data type representing the configuration of Laminar.

     laminar (default: laminar)
          The Laminar package to use.

     home-directory (default: "/var/lib/laminar")
          The directory for job configurations and run directories.

     supplementary-groups (default: ())
          Supplementary groups for the Laminar user account.

     bind-http (default: "*:8080")
          The interface/port or unix socket on which laminard should listen for incoming connections to the web frontend.

     bind-rpc (default: "unix-abstract:laminar")
          The interface/port or unix socket on which laminard should listen for incoming commands such as build triggers.

     title (default: "Laminar")
          The page title to show in the web frontend.

     keep-rundirs (default: 0)
          Set to an integer defining how many rundirs to keep per job.  The lowest-numbered ones will be deleted.  The default is 0, meaning all run dirs will be immediately deleted.

     archive-url (default: #f)
          The web frontend served by laminard will use this URL to form links to artefacts archived jobs.

     base-url (default: #f)
          Base URL to use for links to laminar itself.

Power Management Services
-------------------------

TLP daemon
..........

The (gnu services pm) module provides a Guix service definition for the Linux power management tool TLP.

TLP enables various powersaving modes in userspace and kernel. Contrary to upower-service, it is not a passive, monitoring tool, as it will apply custom settings each time a new power source is detected.  More information can be found at TLP home page (https://linrunner.de/en/tlp/tlp.html).

 -- Variable: tlp-service-type
     The service type for the TLP tool.  The default settings are optimised for battery life on most systems, but you can tweak them to your heart's content by adding a valid tlp-configuration:

          (service tlp-service-type
                   (tlp-configuration
                    (cpu-scaling-governor-on-ac (list "performance"))
                    (sched-powersave-on-bat? #t)))

Each parameter definition is preceded by its type; for example, boolean foo indicates that the foo parameter should be specified as a boolean.  Types starting with maybe- denote parameters that won't show up in TLP config file when their value is left unset, or is explicitly set to the %unset-value value.

Available tlp-configuration fields are:

 -- tlp-configuration parameter: package tlp
     The TLP package.

 -- tlp-configuration parameter: boolean tlp-enable?
     Set to true if you wish to enable TLP.

     Defaults to #t.

 -- tlp-configuration parameter: string tlp-default-mode
     Default mode when no power supply can be detected.  Alternatives are AC and BAT.

     Defaults to "AC".

 -- tlp-configuration parameter: non-negative-integer disk-idle-secs-on-ac
     Number of seconds Linux kernel has to wait after the disk goes idle, before syncing on AC.

     Defaults to 0.

 -- tlp-configuration parameter: non-negative-integer disk-idle-secs-on-bat
     Same as disk-idle-ac but on BAT mode.

     Defaults to 2.

 -- tlp-configuration parameter: non-negative-integer max-lost-work-secs-on-ac
     Dirty pages flushing periodicity, expressed in seconds.

     Defaults to 15.

 -- tlp-configuration parameter: non-negative-integer max-lost-work-secs-on-bat
     Same as max-lost-work-secs-on-ac but on BAT mode.

     Defaults to 60.

 -- tlp-configuration parameter: maybe-space-separated-string-list cpu-scaling-governor-on-ac
     CPU frequency scaling governor on AC mode.  With intel_pstate driver, alternatives are powersave and performance.  With acpi-cpufreq driver, alternatives are ondemand, powersave, performance and conservative.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-space-separated-string-list cpu-scaling-governor-on-bat
     Same as cpu-scaling-governor-on-ac but on BAT mode.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-scaling-min-freq-on-ac
     Set the min available frequency for the scaling governor on AC.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-scaling-max-freq-on-ac
     Set the max available frequency for the scaling governor on AC.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-scaling-min-freq-on-bat
     Set the min available frequency for the scaling governor on BAT.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-scaling-max-freq-on-bat
     Set the max available frequency for the scaling governor on BAT.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-min-perf-on-ac
     Limit the min P-state to control the power dissipation of the CPU, in AC mode.  Values are stated as a percentage of the available performance.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-max-perf-on-ac
     Limit the max P-state to control the power dissipation of the CPU, in AC mode.  Values are stated as a percentage of the available performance.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-min-perf-on-bat
     Same as cpu-min-perf-on-ac on BAT mode.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer cpu-max-perf-on-bat
     Same as cpu-max-perf-on-ac on BAT mode.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-boolean cpu-boost-on-ac?
     Enable CPU turbo boost feature on AC mode.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-boolean cpu-boost-on-bat?
     Same as cpu-boost-on-ac? on BAT mode.

     Defaults to disabled.

 -- tlp-configuration parameter: boolean sched-powersave-on-ac?
     Allow Linux kernel to minimize the number of CPU cores/hyper-threads used under light load conditions.

     Defaults to #f.

 -- tlp-configuration parameter: boolean sched-powersave-on-bat?
     Same as sched-powersave-on-ac? but on BAT mode.

     Defaults to #t.

 -- tlp-configuration parameter: boolean nmi-watchdog?
     Enable Linux kernel NMI watchdog.

     Defaults to #f.

 -- tlp-configuration parameter: maybe-string phc-controls
     For Linux kernels with PHC patch applied, change CPU voltages.  An example value would be "F:V F:V F:V F:V".

     Defaults to disabled.

 -- tlp-configuration parameter: string energy-perf-policy-on-ac
     Set CPU performance versus energy saving policy on AC.  Alternatives are performance, normal, powersave.

     Defaults to "performance".

 -- tlp-configuration parameter: string energy-perf-policy-on-bat
     Same as energy-perf-policy-ac but on BAT mode.

     Defaults to "powersave".

 -- tlp-configuration parameter: space-separated-string-list disks-devices
     Hard disk devices.

 -- tlp-configuration parameter: space-separated-string-list disk-apm-level-on-ac
     Hard disk advanced power management level.

 -- tlp-configuration parameter: space-separated-string-list disk-apm-level-on-bat
     Same as disk-apm-bat but on BAT mode.

 -- tlp-configuration parameter: maybe-space-separated-string-list disk-spindown-timeout-on-ac
     Hard disk spin down timeout.  One value has to be specified for each declared hard disk.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-space-separated-string-list disk-spindown-timeout-on-bat
     Same as disk-spindown-timeout-on-ac but on BAT mode.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-space-separated-string-list disk-iosched
     Select IO scheduler for disk devices.  One value has to be specified for each declared hard disk.  Example alternatives are cfq, deadline and noop.

     Defaults to disabled.

 -- tlp-configuration parameter: string sata-linkpwr-on-ac
     SATA aggressive link power management (ALPM) level.  Alternatives are min_power, medium_power, max_performance.

     Defaults to "max_performance".

 -- tlp-configuration parameter: string sata-linkpwr-on-bat
     Same as sata-linkpwr-ac but on BAT mode.

     Defaults to "min_power".

 -- tlp-configuration parameter: maybe-string sata-linkpwr-blacklist
     Exclude specified SATA host devices for link power management.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-on-off-boolean ahci-runtime-pm-on-ac?
     Enable Runtime Power Management for AHCI controller and disks on AC mode.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-on-off-boolean ahci-runtime-pm-on-bat?
     Same as ahci-runtime-pm-on-ac on BAT mode.

     Defaults to disabled.

 -- tlp-configuration parameter: non-negative-integer ahci-runtime-pm-timeout
     Seconds of inactivity before disk is suspended.

     Defaults to 15.

 -- tlp-configuration parameter: string pcie-aspm-on-ac
     PCI Express Active State Power Management level.  Alternatives are default, performance, powersave.

     Defaults to "performance".

 -- tlp-configuration parameter: string pcie-aspm-on-bat
     Same as pcie-aspm-ac but on BAT mode.

     Defaults to "powersave".

 -- tlp-configuration parameter: maybe-non-negative-integer start-charge-thresh-bat0
     Percentage when battery 0 should begin charging.  Only supported on some laptops.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer stop-charge-thresh-bat0
     Percentage when battery 0 should stop charging.  Only supported on some laptops.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer start-charge-thresh-bat1
     Percentage when battery 1 should begin charging.  Only supported on some laptops.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-non-negative-integer stop-charge-thresh-bat1
     Percentage when battery 1 should stop charging.  Only supported on some laptops.

     Defaults to disabled.

 -- tlp-configuration parameter: string radeon-power-profile-on-ac
     Radeon graphics clock speed level.  Alternatives are low, mid, high, auto, default.

     Defaults to "high".

 -- tlp-configuration parameter: string radeon-power-profile-on-bat
     Same as radeon-power-ac but on BAT mode.

     Defaults to "low".

 -- tlp-configuration parameter: string radeon-dpm-state-on-ac
     Radeon dynamic power management method (DPM).  Alternatives are battery, performance.

     Defaults to "performance".

 -- tlp-configuration parameter: string radeon-dpm-state-on-bat
     Same as radeon-dpm-state-ac but on BAT mode.

     Defaults to "battery".

 -- tlp-configuration parameter: string radeon-dpm-perf-level-on-ac
     Radeon DPM performance level.  Alternatives are auto, low, high.

     Defaults to "auto".

 -- tlp-configuration parameter: string radeon-dpm-perf-level-on-bat
     Same as radeon-dpm-perf-ac but on BAT mode.

     Defaults to "auto".

 -- tlp-configuration parameter: on-off-boolean wifi-pwr-on-ac?
     Wifi power saving mode.

     Defaults to #f.

 -- tlp-configuration parameter: on-off-boolean wifi-pwr-on-bat?
     Same as wifi-power-ac? but on BAT mode.

     Defaults to #t.

 -- tlp-configuration parameter: y-n-boolean wol-disable?
     Disable wake on LAN.

     Defaults to #t.

 -- tlp-configuration parameter: non-negative-integer sound-power-save-on-ac
     Timeout duration in seconds before activating audio power saving on Intel HDA and AC97 devices.  A value of 0 disables power saving.

     Defaults to 0.

 -- tlp-configuration parameter: non-negative-integer sound-power-save-on-bat
     Same as sound-powersave-ac but on BAT mode.

     Defaults to 1.

 -- tlp-configuration parameter: y-n-boolean sound-power-save-controller?
     Disable controller in powersaving mode on Intel HDA devices.

     Defaults to #t.

 -- tlp-configuration parameter: boolean bay-poweroff-on-bat?
     Enable optical drive in UltraBay/MediaBay on BAT mode.  Drive can be powered on again by releasing (and reinserting) the eject lever or by pressing the disc eject button on newer models.

     Defaults to #f.

 -- tlp-configuration parameter: string bay-device
     Name of the optical drive device to power off.

     Defaults to "sr0".

 -- tlp-configuration parameter: string runtime-pm-on-ac
     Runtime Power Management for PCI(e) bus devices.  Alternatives are on and auto.

     Defaults to "on".

 -- tlp-configuration parameter: string runtime-pm-on-bat
     Same as runtime-pm-ac but on BAT mode.

     Defaults to "auto".

 -- tlp-configuration parameter: boolean runtime-pm-all?
     Runtime Power Management for all PCI(e) bus devices, except blacklisted ones.

     Defaults to #t.

 -- tlp-configuration parameter: maybe-space-separated-string-list runtime-pm-blacklist
     Exclude specified PCI(e) device addresses from Runtime Power Management.

     Defaults to disabled.

 -- tlp-configuration parameter: space-separated-string-list runtime-pm-driver-blacklist
     Exclude PCI(e) devices assigned to the specified drivers from Runtime Power Management.

 -- tlp-configuration parameter: boolean usb-autosuspend?
     Enable USB autosuspend feature.

     Defaults to #t.

 -- tlp-configuration parameter: maybe-string usb-blacklist
     Exclude specified devices from USB autosuspend.

     Defaults to disabled.

 -- tlp-configuration parameter: boolean usb-blacklist-wwan?
     Exclude WWAN devices from USB autosuspend.

     Defaults to #t.

 -- tlp-configuration parameter: maybe-string usb-whitelist
     Include specified devices into USB autosuspend, even if they are already excluded by the driver or via usb-blacklist-wwan?.

     Defaults to disabled.

 -- tlp-configuration parameter: maybe-boolean usb-autosuspend-disable-on-shutdown?
     Enable USB autosuspend before shutdown.

     Defaults to disabled.

 -- tlp-configuration parameter: boolean restore-device-state-on-startup?
     Restore radio device state (bluetooth, wifi, wwan) from previous shutdown on system startup.

     Defaults to #f.

Thermald daemon
...............

The (gnu services pm) module provides an interface to thermald, a CPU frequency scaling service which helps prevent overheating.

 -- Variable: thermald-service-type
     This is the service type for thermald (https://01.org/linux-thermal-daemon/), the Linux Thermal Daemon, which is responsible for controlling the thermal state of processors and preventing overheating.

 -- Data Type: thermald-configuration
     Data type representing the configuration of thermald-service-type.

     adaptive? (default: #f)
          Use DPTF (Dynamic Power and Thermal Framework) adaptive tables when present.

     ignore-cpuid-check? (default: #f)
          Ignore cpuid check for supported CPU models.

     thermald (default: THERMALD)
          Package object of thermald.

Audio Services
--------------

The (gnu services audio) module provides a service to start MPD (the Music Player Daemon).

Music Player Daemon
...................

The Music Player Daemon (MPD) is a service that can play music while being controlled from the local machine or over the network by a variety of clients.

The following example shows the simplest configuration to locally expose, via PulseAudio, a music collection kept at /srv/music, with mpd running as the default mpd user.  This user will spawn its own PulseAudio daemon, which may compete for the sound card access with that of your own user.  In this configuration, you may have to stop the playback of your user audio applications to hear MPD's output and vice-versa.

     (service mpd-service-type
              (mpd-configuration
               (music-directory "/srv/music")))

     The music directory must be readable to the MPD user, by default, mpd.  Permission problems will be reported via Permission denied errors in the MPD logs, which appear in /var/log/messages by default.

Most MPD clients will trigger a database update upon connecting, but you can also use the update action do to so:

     herd update mpd

All the MPD configuration fields are documented below, and a more complex example follows.

 -- Variable: mpd-service-type
     The service type for mpd

 -- Data Type: mpd-configuration
     Available mpd-configuration fields are:

     package (default: mpd) (type: file-like)
          The MPD package.

     user (type: user-account)
          The user to run mpd as.

     group (type: user-group)
          The group to run mpd as.

          The default %mpd-group is a system group with name ``mpd''.

     shepherd-requirement (default: '()) (type: list-of-symbols)
          A list of symbols naming Shepherd services that this service will depend on.

     environment-variables (default: '("PULSE_CLIENTCONFIG=/etc/pulse/client.conf" "PULSE_CONFIG=/etc/pulse/daemon.conf")) (type: list-of-strings)
          A list of strings specifying environment variables.

     log-file (type: maybe-string)
          The location of the log file.  Unless specified, logs are sent to the local syslog daemon.  Alternatively, a log file name can be specified, for example /var/log/mpd.log.

     log-level (type: maybe-string)
          Supress any messages below this threshold.  The available values, in decreasing order of verbosity, are: verbose, info, notice, warning and error.

     music-directory (type: maybe-string)
          The directory to scan for music files.

     music-dir (type: maybe-string)
          The directory to scan for music files.

     playlist-directory (type: maybe-string)
          The directory to store playlists.

     playlist-dir (type: maybe-string)
          The directory to store playlists.

     db-file (type: maybe-string)
          The location of the music database.  When left unspecified, ~/.cache/db is used.

     state-file (type: maybe-string)
          The location of the file that stores current MPD's state.

     sticker-file (type: maybe-string)
          The location of the sticker database.

     default-port (default: 6600) (type: maybe-port)
          The default port to run mpd on.

     endpoints (type: maybe-list-of-strings)
          The addresses that mpd will bind to.  A port different from DEFAULT-PORT may be specified, e.g.  localhost:6602 and IPv6 addresses must be enclosed in square brackets when a different port is used.  To use a Unix domain socket, an absolute path or a path starting with ~ can be specified here.

     address (type: maybe-string)
          The address that mpd will bind to.  To use a Unix domain socket, an absolute path can be specified here.

     database (type: maybe-mpd-plugin)
          MPD database plugin configuration.

     partitions (default: '()) (type: list-of-mpd-partition)
          List of MPD "partitions".

     neighbors (default: '()) (type: list-of-mpd-plugin)
          List of MPD neighbor plugin configurations.

     inputs (default: '()) (type: list-of-mpd-plugin)
          List of MPD input plugin configurations.

     archive-plugins (default: '()) (type: list-of-mpd-plugin)
          List of MPD archive plugin configurations.

     auto-update? (type: maybe-boolean)
          Whether to automatically update the music database when files are changed in the MUSIC-DIRECTORY.

     input-cache-size (type: maybe-string)
          MPD input cache size.

     decoders (default: '()) (type: list-of-mpd-plugin)
          List of MPD decoder plugin configurations.

     resampler (type: maybe-mpd-plugin)
          MPD resampler plugin configuration.

     filters (default: '()) (type: list-of-mpd-plugin)
          List of MPD filter plugin configurations.

     outputs (type: list-of-mpd-plugin-or-output)
          The audio outputs that MPD can use.  By default this is a single output using pulseaudio.

     playlist-plugins (default: '()) (type: list-of-mpd-plugin)
          List of MPD playlist plugin configurations.

     extra-options (default: '()) (type: alist)
          An association list of option symbols/strings to string values to be appended to the configuration.

 -- Data Type: mpd-plugin
     Data type representing a mpd plugin.

     plugin (type: maybe-string)
          Plugin name.

     name (type: maybe-string)
          Name.

     enabled? (type: maybe-boolean)
          Whether the plugin is enabled/disabled.

     extra-options (default: '()) (type: alist)
          An association list of option symbols/strings to string values to be appended to the plugin configuration.  See MPD plugin reference (https://mpd.readthedocs.io/en/latest/plugins.html) for available options.

 -- Data Type: mpd-partition
     Data type representing a mpd partition.

     name (type: string)
          Partition name.

     extra-options (default: '()) (type: alist)
          An association list of option symbols/strings to string values to be appended to the partition configuration.  See Configuring Partitions (https://mpd.readthedocs.io/en/latest/user.html#configuring-partitions) for available options.

 -- Data Type: mpd-output
     Available mpd-output fields are:

     name (default: "MPD") (type: string)
          The name of the audio output.

     type (default: "pulse") (type: string)
          The type of audio output.

     enabled? (default: #t) (type: boolean)
          Specifies whether this audio output is enabled when MPD is started.  By default, all audio outputs are enabled.  This is just the default setting when there is no state file; with a state file, the previous state is restored.

     format (type: maybe-string)
          Force a specific audio format on output.  See Global Audio Format (https://mpd.readthedocs.io/en/latest/user.html#audio-output-format) for a more detailed description.

     tags? (default: #t) (type: boolean)
          If set to #f, then MPD will not send tags to this output.  This is only useful for output plugins that can receive tags, for example the httpd output plugin.

     always-on? (default: #f) (type: boolean)
          If set to #t, then MPD attempts to keep this audio output always open.  This may be useful for streaming servers, when you don’t want to disconnect all listeners even when playback is accidentally stopped.

     mixer-type (type: maybe-string)
          This field accepts a string that specifies which mixer should be used for this audio output: the hardware mixer, the software mixer, the null mixer (allows setting the volume, but with no effect; this can be used as a trick to implement an external mixer External Mixer) or no mixer (none).  When left unspecified, a hardware mixer is used for devices that support it.

     replay-gain-handler (type: maybe-string)
          This field accepts a string that specifies how Replay Gain (https://mpd.readthedocs.io/en/latest/user.html#replay-gain) is to be applied.  software uses an internal software volume control, mixer uses the configured (hardware) mixer control and none disables replay gain on this audio output.

     extra-options (default: '()) (type: alist)
          An association list of option symbols/strings to string values to be appended to the audio output configuration.

The following example shows a configuration of mpd that configures some of its plugins and provides a HTTP audio streaming output.

     (service mpd-service-type
              (mpd-configuration
                (outputs
                  (list (mpd-output
                          (name "streaming")
                          (type "httpd")
                          (mixer-type 'null)
                          (extra-options
                           `((encoder . "vorbis")
                             (port    . "8080"))))))
                (decoders
                  (list (mpd-plugin
                          (plugin "mikmod")
                          (enabled? #f))
                        (mpd-plugin
                          (plugin "openmpt")
                          (enabled? #t)
                          (extra-options `((repeat-count . -1)
                                           (interpolation-filter . 1))))))
                (resampler (mpd-plugin
                             (plugin "libsamplerate")
                             (extra-options `((type . 0)))))))

myMPD
.....

myMPD (https://jcorporation.github.io/myMPD/) is a web server frontend for MPD that provides a mobile friendly web client for MPD.

The following example shows a myMPD instance listening on port 80, with album cover caching disabled.

     (service mympd-service-type
              (mympd-configuration
               (port 80)
               (covercache-ttl 0)))

 -- Variable: mympd-service-type
     The service type for mympd.

 -- Data Type: mympd-configuration
     Available mympd-configuration fields are:

     package (default: mympd) (type: file-like)
          The package object of the myMPD server.

     shepherd-requirement (default: '()) (type: list-of-symbols)
          This is a list of symbols naming Shepherd services that this service will depend on.

     user (default: %mympd-user) (type: user-account)
          Owner of the mympd process.

          The default %mympd-user is a system user with the name ``mympd'', who is a part of the group GROUP (see below).

     group (default: %mympd-group) (type: user-group)
          Owner group of the mympd process.

          The default %mympd-group is a system group with name ``mympd''.

     work-directory (default: "/var/lib/mympd") (type: string)
          Where myMPD will store its data.

     cache-directory (default: "/var/cache/mympd") (type: string)
          Where myMPD will store its cache.

     acl (type: maybe-mympd-ip-acl)
          ACL to access the myMPD webserver.

     covercache-ttl (default: 31) (type: maybe-integer)
          How long to keep cached covers, 0 disables cover caching.

     http? (default: #t) (type: boolean)
          HTTP support.

     host (default: "[::]") (type: string)
          Host name to listen on.

     port (default: 80) (type: maybe-port)
          HTTP port to listen on.

     log-level (default: 5) (type: integer)
          How much detail to include in logs, possible values: 0 to 7.

     log-to (type: maybe-string)
          Where to send logs.  Unless specified, the service logs to the local syslog service under the daemon facility.  Alternatively, a log file name can be specified, for example /var/log/mympd.log.

     lualibs (default: "all") (type: maybe-string)
          See https://jcorporation.github.io/myMPD/scripting/#lua-standard-libraries.

     uri (type: maybe-string)
          Override URI to myMPD.  See https://github.com/jcorporation/myMPD/issues/950.

     script-acl (default: (mympd-ip-acl (allow '("127.0.0.1")))) (type: maybe-mympd-ip-acl)
          ACL to access the myMPD script backend.

     ssl? (default: #f) (type: boolean)
          SSL/TLS support.

     ssl-port (default: 443) (type: maybe-port)
          Port to listen for HTTPS.

     ssl-cert (type: maybe-string)
          Path to PEM encoded X.509 SSL/TLS certificate (public key).

     ssl-key (type: maybe-string)
          Path to PEM encoded SSL/TLS private key.

     pin-hash (type: maybe-string)
          SHA-256 hashed pin used by myMPD to control settings access by prompting a pin from the user.

     save-caches? (type: maybe-boolean)
          Whether to preserve caches between service restarts.

 -- Data Type: mympd-ip-acl
     Available mympd-ip-acl fields are:

     allow (default: '()) (type: list-of-strings)
          Allowed IP addresses.

     deny (default: '()) (type: list-of-strings)
          Disallowed IP addresses.

Virtualization Services
-----------------------

The (gnu services virtualization) module provides services for the libvirt and virtlog daemons, as well as other virtualization-related services.

Libvirt daemon
..............

libvirtd is the server side daemon component of the libvirt virtualization management system.  This daemon runs on host servers and performs required management tasks for virtualized guests.  To connect to the libvirt daemon as an unprivileged user, it must be added to the libvirt group, as shown in the example below.

 -- Variable: libvirt-service-type
     This is the type of the libvirt daemon (https://libvirt.org). Its value must be a libvirt-configuration.

          (users (cons (user-account
                        (name "user")
                        (group "users")
                        (supplementary-groups '("libvirt"
                                                "audio" "video" "wheel")))
                       %base-user-accounts))
          (service libvirt-service-type
                   (libvirt-configuration
                    (tls-port "16555")))

Available libvirt-configuration fields are:

 -- libvirt-configuration parameter: package libvirt
     Libvirt package.

 -- libvirt-configuration parameter: boolean listen-tls?
     Flag listening for secure TLS connections on the public TCP/IP port. You must set listen for this to have any effect.

     It is necessary to setup a CA and issue server certificates before using this capability.

     Defaults to #t.

 -- libvirt-configuration parameter: boolean listen-tcp?
     Listen for unencrypted TCP connections on the public TCP/IP port.  You must set listen for this to have any effect.

     Using the TCP socket requires SASL authentication by default.  Only SASL mechanisms which support data encryption are allowed.  This is DIGEST_MD5 and GSSAPI (Kerberos5).

     Defaults to #f.

 -- libvirt-configuration parameter: string tls-port
     Port for accepting secure TLS connections.   This can be a port number, or service name.

     Defaults to "16514".

 -- libvirt-configuration parameter: string tcp-port
     Port for accepting insecure TCP connections.  This can be a port number, or service name.

     Defaults to "16509".

 -- libvirt-configuration parameter: string listen-addr
     IP address or hostname used for client connections.

     Defaults to "0.0.0.0".

 -- libvirt-configuration parameter: boolean mdns-adv?
     Flag toggling mDNS advertisement of the libvirt service.

     Alternatively can disable for all services on a host by stopping the Avahi daemon.

     Defaults to #f.

 -- libvirt-configuration parameter: string mdns-name
     Default mDNS advertisement name.  This must be unique on the immediate broadcast network.

     Defaults to "Virtualization Host <hostname>".

 -- libvirt-configuration parameter: string unix-sock-group
     UNIX domain socket group ownership.  This can be used to allow a 'trusted' set of users access to management capabilities without becoming root.

     Defaults to "libvirt".

 -- libvirt-configuration parameter: string unix-sock-ro-perms
     UNIX socket permissions for the R/O socket.  This is used for monitoring VM status only.

     Defaults to "0777".

 -- libvirt-configuration parameter: string unix-sock-rw-perms
     UNIX socket permissions for the R/W socket.  Default allows only root. If PolicyKit is enabled on the socket, the default will change to allow everyone (eg, 0777)

     Defaults to "0770".

 -- libvirt-configuration parameter: string unix-sock-admin-perms
     UNIX socket permissions for the admin socket.  Default allows only owner (root), do not change it unless you are sure to whom you are exposing the access to.

     Defaults to "0777".

 -- libvirt-configuration parameter: string unix-sock-dir
     The directory in which sockets will be found/created.

     Defaults to "/var/run/libvirt".

 -- libvirt-configuration parameter: string auth-unix-ro
     Authentication scheme for UNIX read-only sockets.  By default socket permissions allow anyone to connect

     Defaults to "polkit".

 -- libvirt-configuration parameter: string auth-unix-rw
     Authentication scheme for UNIX read-write sockets.  By default socket permissions only allow root.  If PolicyKit support was compiled into libvirt, the default will be to use 'polkit' auth.

     Defaults to "polkit".

 -- libvirt-configuration parameter: string auth-tcp
     Authentication scheme for TCP sockets.  If you don't enable SASL, then all TCP traffic is cleartext.  Don't do this outside of a dev/test scenario.

     Defaults to "sasl".

 -- libvirt-configuration parameter: string auth-tls
     Authentication scheme for TLS sockets.  TLS sockets already have encryption provided by the TLS layer, and limited authentication is done by certificates.

     It is possible to make use of any SASL authentication mechanism as well, by using 'sasl' for this option

     Defaults to "none".

 -- libvirt-configuration parameter: optional-list access-drivers
     API access control scheme.

     By default an authenticated user is allowed access to all APIs.  Access drivers can place restrictions on this.

     Defaults to '().

 -- libvirt-configuration parameter: string key-file
     Server key file path.  If set to an empty string, then no private key is loaded.

     Defaults to "".

 -- libvirt-configuration parameter: string cert-file
     Server key file path.  If set to an empty string, then no certificate is loaded.

     Defaults to "".

 -- libvirt-configuration parameter: string ca-file
     Server key file path.  If set to an empty string, then no CA certificate is loaded.

     Defaults to "".

 -- libvirt-configuration parameter: string crl-file
     Certificate revocation list path.  If set to an empty string, then no CRL is loaded.

     Defaults to "".

 -- libvirt-configuration parameter: boolean tls-no-sanity-cert
     Disable verification of our own server certificates.

     When libvirtd starts it performs some sanity checks against its own certificates.

     Defaults to #f.

 -- libvirt-configuration parameter: boolean tls-no-verify-cert
     Disable verification of client certificates.

     Client certificate verification is the primary authentication mechanism. Any client which does not present a certificate signed by the CA will be rejected.

     Defaults to #f.

 -- libvirt-configuration parameter: optional-list tls-allowed-dn-list
     Whitelist of allowed x509 Distinguished Name.

     Defaults to '().

 -- libvirt-configuration parameter: optional-list sasl-allowed-usernames
     Whitelist of allowed SASL usernames.  The format for username depends on the SASL authentication mechanism.

     Defaults to '().

 -- libvirt-configuration parameter: string tls-priority
     Override the compile time default TLS priority string.  The default is usually "NORMAL" unless overridden at build time.  Only set this is it is desired for libvirt to deviate from the global default settings.

     Defaults to "NORMAL".

 -- libvirt-configuration parameter: integer max-clients
     Maximum number of concurrent client connections to allow over all sockets combined.

     Defaults to 5000.

 -- libvirt-configuration parameter: integer max-queued-clients
     Maximum length of queue of connections waiting to be accepted by the daemon.  Note, that some protocols supporting retransmission may obey this so that a later reattempt at connection succeeds.

     Defaults to 1000.

 -- libvirt-configuration parameter: integer max-anonymous-clients
     Maximum length of queue of accepted but not yet authenticated clients. Set this to zero to turn this feature off

     Defaults to 20.

 -- libvirt-configuration parameter: integer min-workers
     Number of workers to start up initially.

     Defaults to 5.

 -- libvirt-configuration parameter: integer max-workers
     Maximum number of worker threads.

     If the number of active clients exceeds min-workers, then more threads are spawned, up to max_workers limit.  Typically you'd want max_workers to equal maximum number of clients allowed.

     Defaults to 20.

 -- libvirt-configuration parameter: integer prio-workers
     Number of priority workers.  If all workers from above pool are stuck, some calls marked as high priority (notably domainDestroy) can be executed in this pool.

     Defaults to 5.

 -- libvirt-configuration parameter: integer max-requests
     Total global limit on concurrent RPC calls.

     Defaults to 20.

 -- libvirt-configuration parameter: integer max-client-requests
     Limit on concurrent requests from a single client connection.  To avoid one client monopolizing the server this should be a small fraction of the global max_requests and max_workers parameter.

     Defaults to 5.

 -- libvirt-configuration parameter: integer admin-min-workers
     Same as min-workers but for the admin interface.

     Defaults to 1.

 -- libvirt-configuration parameter: integer admin-max-workers
     Same as max-workers but for the admin interface.

     Defaults to 5.

 -- libvirt-configuration parameter: integer admin-max-clients
     Same as max-clients but for the admin interface.

     Defaults to 5.

 -- libvirt-configuration parameter: integer admin-max-queued-clients
     Same as max-queued-clients but for the admin interface.

     Defaults to 5.

 -- libvirt-configuration parameter: integer admin-max-client-requests
     Same as max-client-requests but for the admin interface.

     Defaults to 5.

 -- libvirt-configuration parameter: integer log-level
     Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

     Defaults to 3.

 -- libvirt-configuration parameter: string log-filters
     Logging filters.

     A filter allows to select a different logging level for a given category of logs.  The format for a filter is one of:

       * x:name

       * x:+name

     where name is a string which is matched against the category given in the VIR_LOG_INIT() at the top of each libvirt source file, e.g., "remote", "qemu", or "util.json" (the name in the filter can be a substring of the full category name, in order to match multiple similar categories), the optional "+" prefix tells libvirt to log stack trace for each message matching name, and x is the minimal level where matching messages should be logged:

       * 1: DEBUG

       * 2: INFO

       * 3: WARNING

       * 4: ERROR

     Multiple filters can be defined in a single filters statement, they just need to be separated by spaces.

     Defaults to "3:remote 4:event".

 -- libvirt-configuration parameter: string log-outputs
     Logging outputs.

     An output is one of the places to save logging information.  The format for an output can be:

     x:stderr
          output goes to stderr

     x:syslog:name
          use syslog for the output and use the given name as the ident

     x:file:file_path
          output to a file, with the given filepath

     x:journald
          output to journald logging system

     In all case the x prefix is the minimal level, acting as a filter

       * 1: DEBUG

       * 2: INFO

       * 3: WARNING

       * 4: ERROR

     Multiple outputs can be defined, they just need to be separated by spaces.

     Defaults to "3:stderr".

 -- libvirt-configuration parameter: integer audit-level
     Allows usage of the auditing subsystem to be altered

       * 0: disable all auditing

       * 1: enable auditing, only if enabled on host

       * 2: enable auditing, and exit if disabled on host.

     Defaults to 1.

 -- libvirt-configuration parameter: boolean audit-logging
     Send audit messages via libvirt logging infrastructure.

     Defaults to #f.

 -- libvirt-configuration parameter: optional-string host-uuid
     Host UUID.  UUID must not have all digits be the same.

     Defaults to "".

 -- libvirt-configuration parameter: string host-uuid-source
     Source to read host UUID.

       * smbios: fetch the UUID from dmidecode -s system-uuid

       * machine-id: fetch the UUID from /etc/machine-id

     If dmidecode does not provide a valid UUID a temporary UUID will be generated.

     Defaults to "smbios".

 -- libvirt-configuration parameter: integer keepalive-interval
     A keepalive message is sent to a client after keepalive_interval seconds of inactivity to check if the client is still responding.  If set to -1, libvirtd will never send keepalive requests; however clients can still send them and the daemon will send responses.

     Defaults to 5.

 -- libvirt-configuration parameter: integer keepalive-count
     Maximum number of keepalive messages that are allowed to be sent to the client without getting any response before the connection is considered broken.

     In other words, the connection is automatically closed approximately after keepalive_interval * (keepalive_count + 1) seconds since the last message received from the client.  When keepalive-count is set to 0, connections will be automatically closed after keepalive-interval seconds of inactivity without sending any keepalive messages.

     Defaults to 5.

 -- libvirt-configuration parameter: integer admin-keepalive-interval
     Same as above but for admin interface.

     Defaults to 5.

 -- libvirt-configuration parameter: integer admin-keepalive-count
     Same as above but for admin interface.

     Defaults to 5.

 -- libvirt-configuration parameter: integer ovs-timeout
     Timeout for Open vSwitch calls.

     The ovs-vsctl utility is used for the configuration and its timeout option is set by default to 5 seconds to avoid potential infinite waits blocking libvirt.

     Defaults to 5.

Virtlog daemon
..............

The virtlogd service is a server side daemon component of libvirt that is used to manage logs from virtual machine consoles.

This daemon is not used directly by libvirt client applications, rather it is called on their behalf by libvirtd.  By maintaining the logs in a standalone daemon, the main libvirtd daemon can be restarted without risk of losing logs.  The virtlogd daemon has the ability to re-exec() itself upon receiving SIGUSR1, to allow live upgrades without downtime.

 -- Variable: virtlog-service-type
     This is the type of the virtlog daemon. Its value must be a virtlog-configuration.

          (service virtlog-service-type
                   (virtlog-configuration
                    (max-clients 1000)))

 -- libvirt parameter: package libvirt
     Libvirt package.

 -- virtlog-configuration parameter: integer log-level
     Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

     Defaults to 3.

 -- virtlog-configuration parameter: string log-filters
     Logging filters.

     A filter allows to select a different logging level for a given category of logs The format for a filter is one of:

       * x:name

       * x:+name

     where name is a string which is matched against the category given in the VIR_LOG_INIT() at the top of each libvirt source file, e.g., "remote", "qemu", or "util.json" (the name in the filter can be a substring of the full category name, in order to match multiple similar categories), the optional "+" prefix tells libvirt to log stack trace for each message matching name, and x is the minimal level where matching messages should be logged:

       * 1: DEBUG

       * 2: INFO

       * 3: WARNING

       * 4: ERROR

     Multiple filters can be defined in a single filters statement, they just need to be separated by spaces.

     Defaults to "3:remote 4:event".

 -- virtlog-configuration parameter: string log-outputs
     Logging outputs.

     An output is one of the places to save logging information The format for an output can be:

     x:stderr
          output goes to stderr

     x:syslog:name
          use syslog for the output and use the given name as the ident

     x:file:file_path
          output to a file, with the given filepath

     x:journald
          output to journald logging system

     In all case the x prefix is the minimal level, acting as a filter

       * 1: DEBUG

       * 2: INFO

       * 3: WARNING

       * 4: ERROR

     Multiple outputs can be defined, they just need to be separated by spaces.

     Defaults to "3:stderr".

 -- virtlog-configuration parameter: integer max-clients
     Maximum number of concurrent client connections to allow over all sockets combined.

     Defaults to 1024.

 -- virtlog-configuration parameter: integer max-size
     Maximum file size before rolling over.

     Defaults to 2MB

 -- virtlog-configuration parameter: integer max-backups
     Maximum number of backup files to keep.

     Defaults to 3

Transparent Emulation with QEMU
...............................

qemu-binfmt-service-type provides support for transparent emulation of program binaries built for different architectures---e.g., it allows you to transparently execute an ARMv7 program on an x86_64 machine.  It achieves this by combining the QEMU (https://www.qemu.org) emulator and the binfmt_misc feature of the kernel Linux. This feature only allows you to emulate GNU/Linux on a different architecture, but see below for GNU/Hurd support.

 -- Variable: qemu-binfmt-service-type
     This is the type of the QEMU/binfmt service for transparent emulation. Its value must be a qemu-binfmt-configuration object, which specifies the QEMU package to use as well as the architecture we want to emulated:

          (service qemu-binfmt-service-type
                   (qemu-binfmt-configuration
                     (platforms (lookup-qemu-platforms "arm" "aarch64"))))

     In this example, we enable transparent emulation for the ARM and aarch64 platforms.  Running herd stop qemu-binfmt turns it off, and running herd start qemu-binfmt turns it back on (see the herd command (The GNU Shepherd Manual)).

 -- Data Type: qemu-binfmt-configuration
     This is the configuration for the qemu-binfmt service.

     platforms (default: '())
          The list of emulated QEMU platforms.  Each item must be a platform object as returned by lookup-qemu-platforms (see below).

          For example, let's suppose you're on an x86_64 machine and you have this service:

               (service qemu-binfmt-service-type
                        (qemu-binfmt-configuration
                          (platforms (lookup-qemu-platforms "arm"))))

          You can run:

               guix build -s armhf-linux inkscape

          and it will build Inkscape for ARMv7 as if it were a native build, transparently using QEMU to emulate the ARMv7 CPU.  Pretty handy if you'd like to test a package build for an architecture you don't have access to!

     qemu (default: qemu)
          The QEMU package to use.

 -- Procedure: lookup-qemu-platforms platforms...
     Return the list of QEMU platform objects corresponding to PLATFORMS....  PLATFORMS must be a list of strings corresponding to platform names, such as "arm", "sparc", "mips64el", and so on.

 -- Procedure: qemu-platform? obj
     Return true if OBJ is a platform object.

 -- Procedure: qemu-platform-name platform
     Return the name of PLATFORM---a string such as "arm".

QEMU Guest Agent
................

The QEMU guest agent provides control over the emulated system to the host.  The qemu-guest-agent service runs the agent on Guix guests.  To control the agent from the host, open a socket by invoking QEMU with the following arguments:

     qemu-system-x86_64 \
     	-chardev socket,path=/tmp/qga.sock,server=on,wait=off,id=qga0 \
     	-device virtio-serial \
     	-device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0 \
     	...

This creates a socket at /tmp/qga.sock on the host.  Once the guest agent is running, you can issue commands with socat:

     $ guix shell socat -- socat unix-connect:/tmp/qga.sock stdio
     {"execute": "guest-get-host-name"}
     {"return": {"host-name": "guix"}}

See QEMU guest agent documentation (https://wiki.qemu.org/Features/GuestAgent) for more options and commands.

 -- Variable: qemu-guest-agent-service-type
     Service type for the QEMU guest agent service.

 -- Data Type: qemu-guest-agent-configuration
     Configuration for the qemu-guest-agent service.

     qemu (default: qemu-minimal)
          The QEMU package to use.

     device (default: "")
          File name of the device or socket the agent uses to communicate with the host.  If empty, QEMU uses a default file name.

The Hurd in a Virtual Machine
.............................

Service hurd-vm provides support for running GNU/Hurd in a virtual machine (VM), a so-called childhurd.  This service is meant to be used on GNU/Linux and the given GNU/Hurd operating system configuration is cross-compiled.  The virtual machine is a Shepherd service that can be referred to by the names hurd-vm and childhurd and be controlled with commands such as:

     herd start hurd-vm
     herd stop childhurd

When the service is running, you can view its console by connecting to it with a VNC client, for example with:

     guix shell tigervnc-client -- vncviewer localhost:5900

The default configuration (see hurd-vm-configuration below) spawns a secure shell (SSH) server in your GNU/Hurd system, which QEMU (the virtual machine emulator) redirects to port 10022 on the host. By default, the service enables offloading such that the host guix-daemon automatically offloads GNU/Hurd builds to the childhurd (see Daemon Offload Setup).  This is what happens when running a command like the following one, where i586-gnu is the system type of 32-bit GNU/Hurd:

     guix build emacs-minimal -s i586-gnu

The childhurd is volatile and stateless: it starts with a fresh root file system every time you restart it.  By default though, all the files under /etc/childhurd on the host are copied as is to the root file system of the childhurd when it boots.  This allows you to initialize ``secrets'' inside the VM: SSH host keys, authorized substitute keys, and so on---see the explanation of secret-root below.

You will probably find it useful to create an account for you in the GNU/Hurd virtual machine and to authorize logins with your SSH key.  To do that, you can define the GNU/Hurd system in the usual way (see Using the Configuration System), and then pass that operating system as the os field of hurd-vm-configuration, as in this example:

     (define childhurd-os
       ;; Definition of my GNU/Hurd system, derived from the default one.
       (operating-system
         (inherit %hurd-vm-operating-system)

         ;; Add a user account.
         (users (cons (user-account
                       (name "charlie")
                       (comment "This is me!")
                       (group "users")
                       (supplementary-groups '("wheel"))) ;for 'sudo'
                      %base-user-accounts))

         (services
          ;; Modify the SSH configuration to allow login as "root"
          ;; and as "charlie" using public key authentication.
          (modify-services (operating-system-user-services
                            %hurd-vm-operating-system)
            (openssh-service-type
             config => (openssh-configuration
                        (inherit config)
                        (authorized-keys
                         `(("root"
                            ,(local-file
                              "/home/charlie/.ssh/id_rsa.pub"))
                           ("charlie"
                            ,(local-file
                              "/home/charlie/.ssh/id_rsa.pub"))))))))))

     (operating-system
       ;; ...
       (services
         ;; Add the 'hurd-vm' service, configured to use the
         ;; operating system configuration above.
         (append (list (service hurd-vm-service-type
                                (hurd-vm-configuration
                                  (os %childhurd-os))))
                 %base-services)))

That's it!  The remainder of this section provides the reference of the service configuration.

 -- Variable: hurd-vm-service-type
     This is the type of the Hurd in a Virtual Machine service.  Its value must be a hurd-vm-configuration object, which specifies the operating system (see operating-system Reference) and the disk size for the Hurd Virtual Machine, the QEMU package to use as well as the options for running it.

     For example:

          (service hurd-vm-service-type
                   (hurd-vm-configuration
                    (disk-size (* 5000 (expt 2 20))) ;5G
                    (memory-size 1024)))             ;1024MiB

     would create a disk image big enough to build GNU Hello, with some extra memory.

 -- Data Type: hurd-vm-configuration
     The data type representing the configuration for hurd-vm-service-type.

     os (default: %HURD-VM-OPERATING-SYSTEM)
          The operating system to instantiate.  This default is bare-bones with a permissive OpenSSH secure shell daemon listening on port 2222 (see openssh-service-type).

     qemu (default: qemu-minimal)
          The QEMU package to use.

     image (default: HURD-VM-DISK-IMAGE)
          The image object representing the disk image of this virtual machine (see System Images).

     disk-size (default: 'guess)
          The size of the disk image.

     memory-size (default: 512)
          The memory size of the Virtual Machine in mebibytes.

     options (default: '("--snapshot"))
          The extra options for running QEMU.

     id (default: #f)
          If set, a non-zero positive integer used to parameterize Childhurd instances.  It is appended to the service's name, e.g. childhurd1.

     net-options (default: HURD-VM-NET-OPTIONS)
          The procedure used to produce the list of QEMU networking options.

          By default, it produces

               '("--device" "rtl8139,netdev=net0"
                 "--netdev" (string-append
                             "user,id=net0,"
                             "hostfwd=tcp:127.0.0.1:SECRETS-PORT-:1004,"
                             "hostfwd=tcp:127.0.0.1:SSH-PORT-:2222,"
                             "hostfwd=tcp:127.0.0.1:VNC-PORT-:5900"))

          with forwarded ports:

               SECRETS-PORT: (+ 11004 (* 1000 ID))
               SSH-PORT: (+ 10022 (* 1000 ID))
               VNC-PORT: (+ 15900 (* 1000 ID))

     offloading? (default: #t)
          Whether to automatically set up offloading of builds to the childhurd.

          When enabled, this lets you run GNU/Hurd builds on the host and have them transparently offloaded to the VM, for instance when running a command like this:

               guix build coreutils -s i586-gnu

          This option automatically sets up offloading like so:

           1. Authorizing the childhurd's key on the host so that the host accepts build results coming from the childhurd, which can be done like so (see guix archive --authorize, for more on that).

           2. Creating a user account called offloading dedicated to offloading in the childhurd.

           3. Creating an SSH key pair on the host and making it an authorized key of the offloading account in the childhurd.

           4. Adding the childhurd to /etc/guix/machines.scm (see Daemon Offload Setup).

     secret-root (default: /etc/childhurd)
          The root directory with out-of-band secrets to be installed into the childhurd once it runs.  Childhurds are volatile which means that on every startup, secrets such as the SSH host keys and Guix signing key are recreated.

          If the /etc/childhurd directory does not exist, the secret-service running in the Childhurd will be sent an empty list of secrets.

          By default, the service automatically populates /etc/childhurd with the following non-volatile secrets, unless they already exist:

               /etc/childhurd/etc/guix/acl
               /etc/childhurd/etc/guix/signing-key.pub
               /etc/childhurd/etc/guix/signing-key.sec
               /etc/childhurd/etc/ssh/authorized_keys.d/offloading
               /etc/childhurd/etc/ssh/ssh_host_ed25519_key
               /etc/childhurd/etc/ssh/ssh_host_ecdsa_key
               /etc/childhurd/etc/ssh/ssh_host_ed25519_key.pub
               /etc/childhurd/etc/ssh/ssh_host_ecdsa_key.pub

Note that by default the VM image is volatile, i.e., once stopped the contents are lost.  If you want a stateful image instead, override the configuration's image and options without the --snapshot flag using something along these lines:

     (service hurd-vm-service-type
              (hurd-vm-configuration
               (image   (const "/out/of/store/writable/hurd.img"))
               (options '())))

Ganeti
......

     This service is considered experimental.  Configuration options may be changed in a backwards-incompatible manner, and not all features have been thorougly tested.  Users of this service are encouraged to share their experience at guix-devel@gnu.org.

Ganeti is a virtual machine management system.  It is designed to keep virtual machines running on a cluster of servers even in the event of hardware failures, and to make maintenance and recovery tasks easy.  It consists of multiple services which are described later in this section.  In addition to the Ganeti service, you will need the OpenSSH service (see openssh-service-type), and update the /etc/hosts file (see hosts-service-type) with the cluster name and address (or use a DNS server).

All nodes participating in a Ganeti cluster should have the same Ganeti and /etc/hosts configuration.  Here is an example configuration for a Ganeti cluster node that supports multiple storage backends, and installs the debootstrap and guix OS providers:

     (use-package-modules virtualization)
     (use-service-modules base ganeti networking ssh)
     (operating-system
       ;; ...
       (host-name "node1")

       ;; Install QEMU so we can use KVM-based instances, and LVM, DRBD and Ceph
       ;; in order to use the "plain", "drbd" and "rbd" storage backends.
       (packages (append (map specification->package
                              '("qemu" "lvm2" "drbd-utils" "ceph"
                                ;; Add the debootstrap and guix OS providers.
                                "ganeti-instance-guix" "ganeti-instance-debootstrap"))
                         %base-packages))
       (services
        (append (list (service static-networking-service-type
                               (list (static-networking
                                      (addresses
                                       (list (network-address
                                              (device "eth0")
                                              (value "192.168.1.201/24"))))
                                      (routes
                                       (list (network-route
                                              (destination "default")
                                              (gateway "192.168.1.254"))))
                                      (name-servers '("192.168.1.252"
                                                      "192.168.1.253")))))

                      ;; Ganeti uses SSH to communicate between nodes.
                      (service openssh-service-type
                               (openssh-configuration
                                (permit-root-login 'prohibit-password)))

                      (simple-service 'ganeti-hosts-entries hosts-service-type
                                      (list
                                        (host "192.168.1.200" "ganeti.example.com")
                                        (host "192.168.1.201" "node1.example.com"
                                              '("node1"))
                                        (host "192.168.1.202" "node2.example.com"
                                              '("node2"))))

                      (service ganeti-service-type
                               (ganeti-configuration
                                ;; This list specifies allowed file system paths
                                ;; for storing virtual machine images.
                                (file-storage-paths '("/srv/ganeti/file-storage"))
                                ;; This variable configures a single "variant" for
                                ;; both Debootstrap and Guix that works with KVM.
                                (os %default-ganeti-os))))
                %base-services)))

Users are advised to read the Ganeti administrators guide (https://docs.ganeti.org/docs/ganeti/3.0/html/admin.html) to learn about the various cluster options and day-to-day operations.  There is also a blog post (https://guix.gnu.org/blog/2020/running-a-ganeti-cluster-on-guix/) describing how to configure and initialize a small cluster.

 -- Variable: ganeti-service-type
     This is a service type that includes all the various services that Ganeti nodes should run.

     Its value is a ganeti-configuration object that defines the package to use for CLI operations, as well as configuration for the various daemons. Allowed file storage paths and available guest operating systems are also configured through this data type.

 -- Data Type: ganeti-configuration
     The ganeti service takes the following configuration options:

     ganeti (default: ganeti)
          The ganeti package to use.  It will be installed to the system profile and make gnt-cluster, gnt-instance, etc available.  Note that the value specified here does not affect the other services as each refer to a specific ganeti package (see below).

     noded-configuration (default: (ganeti-noded-configuration))
     confd-configuration (default: (ganeti-confd-configuration))
     wconfd-configuration (default: (ganeti-wconfd-configuration))
     luxid-configuration (default: (ganeti-luxid-configuration))
     rapi-configuration (default: (ganeti-rapi-configuration))
     kvmd-configuration (default: (ganeti-kvmd-configuration))
     mond-configuration (default: (ganeti-mond-configuration))
     metad-configuration (default: (ganeti-metad-configuration))
     watcher-configuration (default: (ganeti-watcher-configuration))
     cleaner-configuration (default: (ganeti-cleaner-configuration))

          These options control the various daemons and cron jobs that are distributed with Ganeti.  The possible values for these are described in detail below. To override a setting, you must use the configuration type for that service:

               (service ganeti-service-type
                        (ganeti-configuration
                         (rapi-configuration
                          (ganeti-rapi-configuration
                           (interface "eth1"))))
                         (watcher-configuration
                          (ganeti-watcher-configuration
                           (rapi-ip "10.0.0.1"))))

     file-storage-paths (default: '())
          List of allowed directories for file storage backend.

     hooks (default: #f)
          When set, this should be a file-like object containing a directory with cluster execution hooks (https://docs.ganeti.org/docs/ganeti/3.0/html/hooks.html).

     os (default: %default-ganeti-os)
          List of <ganeti-os> records.

     In essence ganeti-service-type is shorthand for declaring each service individually:

          (service ganeti-noded-service-type)
          (service ganeti-confd-service-type)
          (service ganeti-wconfd-service-type)
          (service ganeti-luxid-service-type)
          (service ganeti-kvmd-service-type)
          (service ganeti-mond-service-type)
          (service ganeti-metad-service-type)
          (service ganeti-watcher-service-type)
          (service ganeti-cleaner-service-type)

     Plus a service extension for etc-service-type that configures the file storage backend and OS variants.

 -- Data Type: ganeti-os
     This data type is suitable for passing to the os parameter of ganeti-configuration.  It takes the following parameters:

     name
          The name for this OS provider.  It is only used to specify where the configuration ends up.  Setting it to ``debootstrap'' will create /etc/ganeti/instance-debootstrap.

     extension (default: #f)
          The file extension for variants of this OS type.  For example .conf or .scm.  It will be appended to the variant file name if set.

     variants (default: '())
          This must be either a list of ganeti-os-variant objects for this OS, or a ``file-like'' object (see file-like objects) representing the variants directory.

          To use the Guix OS provider with variant definitions residing in a local directory instead of declaring individual variants (see GUIX-VARIANTS below), you can do:

               (ganeti-os
                (name "guix")
                (variants (local-file "ganeti-guix-variants"
                                      #:recursive? #true)))

          Note that you will need to maintain the variants.list file (see ganeti-os-interface(7) (https://docs.ganeti.org/docs/ganeti/3.0/man/ganeti-os-interface.html)) manually in this case.

 -- Data Type: ganeti-os-variant
     This is the data type for a Ganeti OS variant.  It takes the following parameters:

     name
          The name of this variant.

     configuration
          A configuration file for this variant.

 -- Variable: %default-debootstrap-hooks
     This variable contains hooks to configure networking and the GRUB bootloader.

 -- Variable: %default-debootstrap-extra-pkgs
     This variable contains a list of packages suitable for a fully-virtualized guest.

 -- Data Type: debootstrap-configuration

     This data type creates configuration files suitable for the debootstrap OS provider.

     hooks (default: %default-debootstrap-hooks)
          When not #f, this must be a G-expression that specifies a directory with scripts that will run when the OS is installed.  It can also be a list of (name . file-like) pairs.  For example:

               `((99-hello-world . ,(plain-file "#!/bin/sh\necho Hello, World")))

          That will create a directory with one executable named 99-hello-world and run it every time this variant is installed.  If set to #f, hooks in /etc/ganeti/instance-debootstrap/hooks will be used, if any.

     proxy (default: #f)
          Optional HTTP proxy to use.

     mirror (default: #f)
          The Debian mirror.  Typically something like http://ftp.no.debian.org/debian. The default varies depending on the distribution.

     arch (default: #f)
          The dpkg architecture.  Set to armhf to debootstrap an ARMv7 instance on an AArch64 host.  Default is to use the current system architecture.

     suite (default: "stable")
          When set, this must be a Debian distribution ``suite'' such as buster or focal.  If set to #f, the default for the OS provider is used.

     extra-pkgs (default: %default-debootstrap-extra-pkgs)
          List of extra packages that will get installed by dpkg in addition to the minimal system.

     components (default: #f)
          When set, must be a list of Debian repository ``components''.  For example '("main" "contrib").

     generate-cache? (default: #t)
          Whether to automatically cache the generated debootstrap archive.

     clean-cache (default: 14)
          Discard the cache after this amount of days.  Use #f to never clear the cache.

     partition-style (default: 'msdos)
          The type of partition to create.  When set, it must be one of 'msdos, 'none or a string.

     partition-alignment (default: 2048)
          Alignment of the partition in sectors.

 -- Procedure: debootstrap-variant name configuration
     This is a helper procedure that creates a ganeti-os-variant record.  It takes two parameters: a name and a debootstrap-configuration object.

 -- Procedure: debootstrap-os variants...
     This is a helper procedure that creates a ganeti-os record.  It takes a list of variants created with debootstrap-variant.

 -- Procedure: guix-variant name configuration
     This is a helper procedure that creates a ganeti-os-variant record for use with the Guix OS provider.  It takes a name and a G-expression that returns a ``file-like'' (see file-like objects) object containing a Guix System configuration.

 -- Procedure: guix-os variants...
     This is a helper procedure that creates a ganeti-os record.  It takes a list of variants produced by guix-variant.

 -- Variable: %default-debootstrap-variants
     This is a convenience variable to make the debootstrap provider work ``out of the box'' without users having to declare variants manually.  It contains a single debootstrap variant with the default configuration:

          (list (debootstrap-variant
                 "default"
                 (debootstrap-configuration)))

 -- Variable: %default-guix-variants
     This is a convenience variable to make the Guix OS provider work without additional configuration.  It creates a virtual machine that has an SSH server, a serial console, and authorizes the Ganeti hosts SSH keys.

          (list (guix-variant
                 "default"
                 (file-append ganeti-instance-guix
                              "/share/doc/ganeti-instance-guix/examples/dynamic.scm")))

Users can implement support for OS providers unbeknownst to Guix by extending the ganeti-os and ganeti-os-variant records appropriately. For example:

     (ganeti-os
      (name "custom")
      (extension ".conf")
      (variants
       (list (ganeti-os-variant
              (name "foo")
              (configuration (plain-file "bar" "this is fine"))))))

That creates /etc/ganeti/instance-custom/variants/foo.conf which points to a file in the store with contents this is fine.  It also creates /etc/ganeti/instance-custom/variants/variants.list with contents foo.

Obviously this may not work for all OS providers out there.  If you find the interface limiting, please reach out to guix-devel@gnu.org.

The rest of this section documents the various services that are included by ganeti-service-type.

 -- Variable: ganeti-noded-service-type
     ganeti-noded is the daemon responsible for node-specific functions within the Ganeti system.  The value of this service must be a ganeti-noded-configuration object.

 -- Data Type: ganeti-noded-configuration
     This is the configuration for the ganeti-noded service.

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     port (default: 1811)
          The TCP port on which the node daemon listens for network requests.

     address (default: "0.0.0.0")
          The network address that the daemon will bind to.  The default address means bind to all available addresses.

     interface (default: #f)
          When this is set, it must be a specific network interface (e.g. eth0) that the daemon will bind to.

     max-clients (default: 20)
          This sets a limit on the maximum number of simultaneous client connections that the daemon will handle.  Connections above this count are accepted, but no responses will be sent until enough connections have closed.

     ssl? (default: #t)
          Whether to use SSL/TLS to encrypt network communications.  The certificate is automatically provisioned by the cluster and can be rotated with gnt-cluster renew-crypto.

     ssl-key (default: "/var/lib/ganeti/server.pem")
          This can be used to provide a specific encryption key for TLS communications.

     ssl-cert (default: "/var/lib/ganeti/server.pem")
          This can be used to provide a specific certificate for TLS communications.

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes. Note that this will leak encryption details to the log files, use with caution.

 -- Variable: ganeti-confd-service-type
     ganeti-confd answers queries related to the configuration of a Ganeti cluster.  The purpose of this daemon is to have a highly available and fast way to query cluster configuration values.  It is automatically active on all master candidates.  The value of this service must be a ganeti-confd-configuration object.

 -- Data Type: ganeti-confd-configuration
     This is the configuration for the ganeti-confd service.

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     port (default: 1814)
          The UDP port on which to listen for network requests.

     address (default: "0.0.0.0")
          Network address that the daemon will bind to.

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes.

 -- Variable: ganeti-wconfd-service-type
     ganeti-wconfd is the daemon that has authoritative knowledge about the cluster configuration and is the only entity that can accept changes to it.  All jobs that need to modify the configuration will do so by sending appropriate requests to this daemon.  It only runs on the master node and will automatically disable itself on other nodes.

     The value of this service must be a ganeti-wconfd-configuration object.

 -- Data Type: ganeti-wconfd-configuration
     This is the configuration for the ganeti-wconfd service.

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     no-voting? (default: #f)
          The daemon will refuse to start if the majority of cluster nodes does not agree that it is running on the master node.  Set to #t to start even if a quorum can not be reached (dangerous, use with caution).

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes.

 -- Variable: ganeti-luxid-service-type
     ganeti-luxid is a daemon used to answer queries related to the configuration and the current live state of a Ganeti cluster.  Additionally, it is the authoritative daemon for the Ganeti job queue.   Jobs can be submitted via this daemon and it schedules and starts them.

     It takes a ganeti-luxid-configuration object.

 -- Data Type: ganeti-luxid-configuration
     This is the configuration for the ganeti-luxid service.

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     no-voting? (default: #f)
          The daemon will refuse to start if it cannot verify that the majority of cluster nodes believes that it is running on the master node.  Set to #t to ignore such checks and start anyway (this can be dangerous).

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes.

 -- Variable: ganeti-rapi-service-type
     ganeti-rapi provides a remote API for Ganeti clusters.  It runs on the master node and can be used to perform cluster actions programmatically via a JSON-based RPC protocol.

     Most query operations are allowed without authentication (unless REQUIRE-AUTHENTICATION? is set), whereas write operations require explicit authorization via the /var/lib/ganeti/rapi/users file.  See the Ganeti Remote API documentation (https://docs.ganeti.org/docs/ganeti/3.0/html/rapi.html) for more information.

     The value of this service must be a ganeti-rapi-configuration object.

 -- Data Type: ganeti-rapi-configuration
     This is the configuration for the ganeti-rapi service.

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     require-authentication? (default: #f)
          Whether to require authentication even for read-only operations.

     port (default: 5080)
          The TCP port on which to listen to API requests.

     address (default: "0.0.0.0")
          The network address that the service will bind to.  By default it listens on all configured addresses.

     interface (default: #f)
          When set, it must specify a specific network interface such as eth0 that the daemon will bind to.

     max-clients (default: 20)
          The maximum number of simultaneous client requests to handle.  Further connections are allowed, but no responses are sent until enough connections have closed.

     ssl? (default: #t)
          Whether to use SSL/TLS encryption on the RAPI port.

     ssl-key (default: "/var/lib/ganeti/server.pem")
          This can be used to provide a specific encryption key for TLS communications.

     ssl-cert (default: "/var/lib/ganeti/server.pem")
          This can be used to provide a specific certificate for TLS communications.

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes. Note that this will leak encryption details to the log files, use with caution.

 -- Variable: ganeti-kvmd-service-type
     ganeti-kvmd is responsible for determining whether a given KVM instance was shut down by an administrator or a user.  Normally Ganeti will restart an instance that was not stopped through Ganeti itself.  If the cluster option user_shutdown is true, this daemon monitors the QMP socket provided by QEMU and listens for shutdown events, and marks the instance as USER_down instead of ERROR_down when it shuts down gracefully by itself.

     It takes a ganeti-kvmd-configuration object.

 -- Data Type: ganeti-kvmd-configuration

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes.

 -- Variable: ganeti-mond-service-type
     ganeti-mond is an optional daemon that provides Ganeti monitoring functionality.  It is responsible for running data collectors and publish the collected information through a HTTP interface.

     It takes a ganeti-mond-configuration object.

 -- Data Type: ganeti-mond-configuration

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     port (default: 1815)
          The port on which the daemon will listen.

     address (default: "0.0.0.0")
          The network address that the daemon will bind to.  By default it binds to all available interfaces.

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes.

 -- Variable: ganeti-metad-service-type
     ganeti-metad is an optional daemon that can be used to provide information about the cluster to instances or OS install scripts.

     It takes a ganeti-metad-configuration object.

 -- Data Type: ganeti-metad-configuration

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     port (default: 80)
          The port on which the daemon will listen.

     address (default: #f)
          If set, the daemon will bind to this address only.  If left unset, the behavior depends on the cluster configuration.

     debug? (default: #f)
          When true, the daemon performs additional logging for debugging purposes.

 -- Variable: ganeti-watcher-service-type
     ganeti-watcher is a script designed to run periodically and ensure the health of a cluster.  It will automatically restart instances that have stopped without Ganeti's consent, and repairs DRBD links in case a node has rebooted.  It also archives old cluster jobs and restarts Ganeti daemons that are not running.  If the cluster parameter ensure_node_health is set, the watcher will also shutdown instances and DRBD devices if the node it is running on is declared offline by known master candidates.

     It can be paused on all nodes with gnt-cluster watcher pause.

     The service takes a ganeti-watcher-configuration object.

 -- Data Type: ganeti-watcher-configuration

     ganeti (default: ganeti)
          The ganeti package to use for this service.

     schedule (default: '(next-second-from (next-minute (range 0 60 5))))
          How often to run the script.  The default is every five minutes.

     rapi-ip (default: #f)
          This option needs to be specified only if the RAPI daemon is configured to use a particular interface or address.  By default the cluster address is used.

     job-age (default: (* 6 3600))
          Archive cluster jobs older than this age, specified in seconds.  The default is 6 hours.  This keeps gnt-job list manageable.

     verify-disks? (default: #t)
          If this is #f, the watcher will not try to repair broken DRBD links automatically.  Administrators will need to use gnt-cluster verify-disks manually instead.

     debug? (default: #f)
          When #t, the script performs additional logging for debugging purposes.

 -- Variable: ganeti-cleaner-service-type
     ganeti-cleaner is a script designed to run periodically and remove old files from the cluster.  This service type controls two cron jobs: one intended for the master node that permanently purges old cluster jobs, and one intended for every node that removes expired X509 certificates, keys, and outdated ganeti-watcher information.  Like all Ganeti services, it is safe to include even on non-master nodes as it will disable itself as necessary.

     It takes a ganeti-cleaner-configuration object.

 -- Data Type: ganeti-cleaner-configuration

     ganeti (default: ganeti)
          The ganeti package to use for the gnt-cleaner command.

     master-schedule (default: "45 1 * * *")
          How often to run the master cleaning job.  The default is once per day, at 01:45:00.

     node-schedule (default: "45 2 * * *")
          How often to run the node cleaning job.  The default is once per day, at 02:45:00.

Version Control Services
------------------------

The (gnu services version-control) module provides a service to allow remote access to local Git repositories.  There are three options: the git-daemon-service-type, which provides access to repositories via the git:// unsecured TCP-based protocol, extending the nginx web server to proxy some requests to git-http-backend, or providing a web interface with cgit-service-type.

 -- Variable: git-daemon-service-type
     Type for a service that runs git daemon, a simple TCP server to expose repositories over the Git protocol for anonymous access.

     The value for this service type is a <git-daemon-configuration> record, by default it allows read-only access to exported (By creating the magic file git-daemon-export-ok in the repository directory.) repositories under /srv/git.

 -- Data Type: git-daemon-configuration
     Data type representing the configuration for git-daemon-service-type.

     package (default: git)
          Package object of the Git distributed version control system.

     export-all? (default: #f)
          Whether to allow access for all Git repositories, even if they do not have the git-daemon-export-ok file.

     base-path (default: /srv/git)
          Whether to remap all the path requests as relative to the given path. If you run git daemon with (base-path "/srv/git") on example.com, then if you later try to pull git://example.com/hello.git, git daemon will interpret the path as /srv/git/hello.git.

     user-path (default: #f)
          Whether to allow ~user notation to be used in requests.  When specified with empty string, requests to git://host/~alice/foo is taken as a request to access foo repository in the home directory of user alice.  If (user-path "PATH") is specified, the same request is taken as a request to access PATH/foo repository in the home directory of user alice.

     listen (default: '())
          Whether to listen on specific IP addresses or hostnames, defaults to all.

     port (default: #f)
          Whether to listen on an alternative port, which defaults to 9418.

     whitelist (default: '())
          If not empty, only allow access to this list of directories.

     extra-options (default: '())
          Extra options that will be passed to git daemon. (Run man git-daemon for more information.)

The git:// protocol lacks authentication.  When you pull from a repository fetched via git://, you don't know whether the data you receive was modified or is even coming from the specified host, and your connection is subject to eavesdropping.  It's better to use an authenticated and encrypted transport, such as https.  Although Git allows you to serve repositories using unsophisticated file-based web servers, there is a faster protocol implemented by the git-http-backend program.  This program is the back-end of a proper Git web service.  It is designed to sit behind a FastCGI proxy.  See Web Services, for more on running the necessary fcgiwrap daemon.

Guix has a separate configuration data type for serving Git repositories over HTTP.

 -- Data Type: git-http-configuration
     Data type representing the configuration for a future git-http-service-type; can currently be used to configure Nginx through git-http-nginx-location-configuration.

     package (default: GIT)
          Package object of the Git distributed version control system.

     git-root (default: /srv/git)
          Directory containing the Git repositories to expose to the world.

     export-all? (default: #f)
          Whether to expose access for all Git repositories in GIT-ROOT, even if they do not have the git-daemon-export-ok file.

     uri-path (default: /git/)
          Path prefix for Git access.  With the default /git/ prefix, this will map http://SERVER/git/REPO.git to /srv/git/REPO.git.  Requests whose URI paths do not begin with this prefix are not passed on to this Git instance.

     fcgiwrap-socket (default: 127.0.0.1:9000)
          The socket on which the fcgiwrap daemon is listening.  See Web Services.

There is no git-http-service-type, currently; instead you can create an nginx-location-configuration from a git-http-configuration and then add that location to a web server.

 -- Procedure: git-http-nginx-location-configuration
     [config=(git-http-configuration)]
     Compute an nginx-location-configuration that corresponds to the given Git http configuration.  An example nginx service definition to serve the default /srv/git over HTTPS might be:

          (service nginx-service-type
                   (nginx-configuration
                    (server-blocks
                     (list
                      (nginx-server-configuration
                       (listen '("443 ssl"))
                       (server-name "git.my-host.org")
                       (ssl-certificate
                        "/etc/certs/git.my-host.org/fullchain.pem")
                       (ssl-certificate-key
                        "/etc/certs/git.my-host.org/privkey.pem")
                       (locations
                        (list
                         (git-http-nginx-location-configuration
                          (git-http-configuration (uri-path "/"))))))))))

     This example assumes that you are using Let's Encrypt to get your TLS certificate.  See Certificate Services.  The default certbot service will redirect all HTTP traffic on git.my-host.org to HTTPS.  You will also need to add an fcgiwrap proxy to your system services.  See Web Services.

Cgit Service
............

Cgit (https://git.zx2c4.com/cgit/) is a web frontend for Git repositories written in C.

The following example will configure the service with default values. By default, Cgit can be accessed on port 80 (http://localhost:80).

     (service cgit-service-type)

The file-object type designates either a file-like object (see file-like objects) or a string.

Available cgit-configuration fields are:

 -- cgit-configuration parameter: package package
     The CGIT package.

 -- cgit-configuration parameter: nginx-server-configuration-list nginx
     NGINX configuration.

 -- cgit-configuration parameter: file-object about-filter
     Specifies a command which will be invoked to format the content of about pages (both top-level and for each repository).

     Defaults to "".

 -- cgit-configuration parameter: string agefile
     Specifies a path, relative to each repository path, which can be used to specify the date and time of the youngest commit in the repository.

     Defaults to "".

 -- cgit-configuration parameter: file-object auth-filter
     Specifies a command that will be invoked for authenticating repository access.

     Defaults to "".

 -- cgit-configuration parameter: string branch-sort
     Flag which, when set to age, enables date ordering in the branch ref list, and when set name enables ordering by branch name.

     Defaults to "name".

 -- cgit-configuration parameter: string cache-root
     Path used to store the cgit cache entries.

     Defaults to "/var/cache/cgit".

 -- cgit-configuration parameter: integer cache-static-ttl
     Number which specifies the time-to-live, in minutes, for the cached version of repository pages accessed with a fixed SHA1.

     Defaults to -1.

 -- cgit-configuration parameter: integer cache-dynamic-ttl
     Number which specifies the time-to-live, in minutes, for the cached version of repository pages accessed without a fixed SHA1.

     Defaults to 5.

 -- cgit-configuration parameter: integer cache-repo-ttl
     Number which specifies the time-to-live, in minutes, for the cached version of the repository summary page.

     Defaults to 5.

 -- cgit-configuration parameter: integer cache-root-ttl
     Number which specifies the time-to-live, in minutes, for the cached version of the repository index page.

     Defaults to 5.

 -- cgit-configuration parameter: integer cache-scanrc-ttl
     Number which specifies the time-to-live, in minutes, for the result of scanning a path for Git repositories.

     Defaults to 15.

 -- cgit-configuration parameter: integer cache-about-ttl
     Number which specifies the time-to-live, in minutes, for the cached version of the repository about page.

     Defaults to 15.

 -- cgit-configuration parameter: integer cache-snapshot-ttl
     Number which specifies the time-to-live, in minutes, for the cached version of snapshots.

     Defaults to 5.

 -- cgit-configuration parameter: integer cache-size
     The maximum number of entries in the cgit cache.  When set to 0, caching is disabled.

     Defaults to 0.

 -- cgit-configuration parameter: boolean case-sensitive-sort?
     Sort items in the repo list case sensitively.

     Defaults to #t.

 -- cgit-configuration parameter: list clone-prefix
     List of common prefixes which, when combined with a repository URL, generates valid clone URLs for the repository.

     Defaults to '().

 -- cgit-configuration parameter: list clone-url
     List of clone-url templates.

     Defaults to '().

 -- cgit-configuration parameter: file-object commit-filter
     Command which will be invoked to format commit messages.

     Defaults to "".

 -- cgit-configuration parameter: string commit-sort
     Flag which, when set to date, enables strict date ordering in the commit log, and when set to topo enables strict topological ordering.

     Defaults to "git log".

 -- cgit-configuration parameter: file-object css
     URL which specifies the css document to include in all cgit pages.

     Defaults to "/share/cgit/cgit.css".

 -- cgit-configuration parameter: file-object email-filter
     Specifies a command which will be invoked to format names and email address of committers, authors, and taggers, as represented in various places throughout the cgit interface.

     Defaults to "".

 -- cgit-configuration parameter: boolean embedded?
     Flag which, when set to #t, will make cgit generate a HTML fragment suitable for embedding in other HTML pages.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-commit-graph?
     Flag which, when set to #t, will make cgit print an ASCII-art commit history graph to the left of the commit messages in the repository log page.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-filter-overrides?
     Flag which, when set to #t, allows all filter settings to be overridden in repository-specific cgitrc files.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-follow-links?
     Flag which, when set to #t, allows users to follow a file in the log view.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-http-clone?
     If set to #t, cgit will act as an dumb HTTP endpoint for Git clones.

     Defaults to #t.

 -- cgit-configuration parameter: boolean enable-index-links?
     Flag which, when set to #t, will make cgit generate extra links "summary", "commit", "tree" for each repo in the repository index.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-index-owner?
     Flag which, when set to #t, will make cgit display the owner of each repo in the repository index.

     Defaults to #t.

 -- cgit-configuration parameter: boolean enable-log-filecount?
     Flag which, when set to #t, will make cgit print the number of modified files for each commit on the repository log page.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-log-linecount?
     Flag which, when set to #t, will make cgit print the number of added and removed lines for each commit on the repository log page.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-remote-branches?
     Flag which, when set to #t, will make cgit display remote branches in the summary and refs views.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-subject-links?
     Flag which, when set to 1, will make cgit use the subject of the parent commit as link text when generating links to parent commits in commit view.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-html-serving?
     Flag which, when set to #t, will make cgit use the subject of the parent commit as link text when generating links to parent commits in commit view.

     Defaults to #f.

 -- cgit-configuration parameter: boolean enable-tree-linenumbers?
     Flag which, when set to #t, will make cgit generate linenumber links for plaintext blobs printed in the tree view.

     Defaults to #t.

 -- cgit-configuration parameter: boolean enable-git-config?
     Flag which, when set to #f, will allow cgit to use Git config to set any repo specific settings.

     Defaults to #f.

 -- cgit-configuration parameter: file-object favicon
     URL used as link to a shortcut icon for cgit.

     Defaults to "/favicon.ico".

 -- cgit-configuration parameter: string footer
     The content of the file specified with this option will be included verbatim at the bottom of all pages (i.e. it replaces the standard "generated by..." message).

     Defaults to "".

 -- cgit-configuration parameter: string head-include
     The content of the file specified with this option will be included verbatim in the HTML HEAD section on all pages.

     Defaults to "".

 -- cgit-configuration parameter: string header
     The content of the file specified with this option will be included verbatim at the top of all pages.

     Defaults to "".

 -- cgit-configuration parameter: file-object include
     Name of a configfile to include before the rest of the current config- file is parsed.

     Defaults to "".

 -- cgit-configuration parameter: string index-header
     The content of the file specified with this option will be included verbatim above the repository index.

     Defaults to "".

 -- cgit-configuration parameter: string index-info
     The content of the file specified with this option will be included verbatim below the heading on the repository index page.

     Defaults to "".

 -- cgit-configuration parameter: boolean local-time?
     Flag which, if set to #t, makes cgit print commit and tag times in the servers timezone.

     Defaults to #f.

 -- cgit-configuration parameter: file-object logo
     URL which specifies the source of an image which will be used as a logo on all cgit pages.

     Defaults to "/share/cgit/cgit.png".

 -- cgit-configuration parameter: string logo-link
     URL loaded when clicking on the cgit logo image.

     Defaults to "".

 -- cgit-configuration parameter: file-object owner-filter
     Command which will be invoked to format the Owner column of the main page.

     Defaults to "".

 -- cgit-configuration parameter: integer max-atom-items
     Number of items to display in atom feeds view.

     Defaults to 10.

 -- cgit-configuration parameter: integer max-commit-count
     Number of entries to list per page in "log" view.

     Defaults to 50.

 -- cgit-configuration parameter: integer max-message-length
     Number of commit message characters to display in "log" view.

     Defaults to 80.

 -- cgit-configuration parameter: integer max-repo-count
     Specifies the number of entries to list per page on the repository index page.

     Defaults to 50.

 -- cgit-configuration parameter: integer max-repodesc-length
     Specifies the maximum number of repo description characters to display on the repository index page.

     Defaults to 80.

 -- cgit-configuration parameter: integer max-blob-size
     Specifies the maximum size of a blob to display HTML for in KBytes.

     Defaults to 0.

 -- cgit-configuration parameter: string max-stats
     Maximum statistics period.  Valid values are week,month, quarter and year.

     Defaults to "".

 -- cgit-configuration parameter: mimetype-alist mimetype
     Mimetype for the specified filename extension.

     Defaults to '((gif "image/gif") (html "text/html") (jpg "image/jpeg") (jpeg "image/jpeg") (pdf "application/pdf") (png "image/png") (svg "image/svg+xml")).

 -- cgit-configuration parameter: file-object mimetype-file
     Specifies the file to use for automatic mimetype lookup.

     Defaults to "".

 -- cgit-configuration parameter: string module-link
     Text which will be used as the formatstring for a hyperlink when a submodule is printed in a directory listing.

     Defaults to "".

 -- cgit-configuration parameter: boolean nocache?
     If set to the value #t caching will be disabled.

     Defaults to #f.

 -- cgit-configuration parameter: boolean noplainemail?
     If set to #t showing full author email addresses will be disabled.

     Defaults to #f.

 -- cgit-configuration parameter: boolean noheader?
     Flag which, when set to #t, will make cgit omit the standard header on all pages.

     Defaults to #f.

 -- cgit-configuration parameter: project-list project-list
     A list of subdirectories inside of repository-directory, relative to it, that should loaded as Git repositories.  An empty list means that all subdirectories will be loaded.

     Defaults to '().

 -- cgit-configuration parameter: file-object readme
     Text which will be used as default repository-cgit-configuration readme.

     Defaults to "".

 -- cgit-configuration parameter: boolean remove-suffix?
     If set to #t and repository-directory is enabled, if any repositories are found with a suffix of .git, this suffix will be removed for the URL and name.

     Defaults to #f.

 -- cgit-configuration parameter: integer renamelimit
     Maximum number of files to consider when detecting renames.

     Defaults to -1.

 -- cgit-configuration parameter: string repository-sort
     The way in which repositories in each section are sorted.

     Defaults to "".

 -- cgit-configuration parameter: robots-list robots
     Text used as content for the robots meta-tag.

     Defaults to '("noindex" "nofollow").

 -- cgit-configuration parameter: string root-desc
     Text printed below the heading on the repository index page.

     Defaults to "a fast webinterface for the git dscm".

 -- cgit-configuration parameter: string root-readme
     The content of the file specified with this option will be included verbatim below the ``about'' link on the repository index page.

     Defaults to "".

 -- cgit-configuration parameter: string root-title
     Text printed as heading on the repository index page.

     Defaults to "".

 -- cgit-configuration parameter: boolean scan-hidden-path
     If set to #t and repository-directory is enabled, repository-directory will recurse into directories whose name starts with a period.  Otherwise, repository-directory will stay away from such directories, considered as ``hidden''.  Note that this does not apply to the .git directory in non-bare repos.

     Defaults to #f.

 -- cgit-configuration parameter: list snapshots
     Text which specifies the default set of snapshot formats that cgit generates links for.

     Defaults to '().

 -- cgit-configuration parameter: repository-directory repository-directory
     Name of the directory to scan for repositories (represents scan-path).

     Defaults to "/srv/git".

 -- cgit-configuration parameter: string section
     The name of the current repository section - all repositories defined after this option will inherit the current section name.

     Defaults to "".

 -- cgit-configuration parameter: string section-sort
     Flag which, when set to 1, will sort the sections on the repository listing by name.

     Defaults to "".

 -- cgit-configuration parameter: integer section-from-path
     A number which, if defined prior to repository-directory, specifies how many path elements from each repo path to use as a default section name.

     Defaults to 0.

 -- cgit-configuration parameter: boolean side-by-side-diffs?
     If set to #t shows side-by-side diffs instead of unidiffs per default.

     Defaults to #f.

 -- cgit-configuration parameter: file-object source-filter
     Specifies a command which will be invoked to format plaintext blobs in the tree view.

     Defaults to "".

 -- cgit-configuration parameter: integer summary-branches
     Specifies the number of branches to display in the repository ``summary'' view.

     Defaults to 10.

 -- cgit-configuration parameter: integer summary-log
     Specifies the number of log entries to display in the repository ``summary'' view.

     Defaults to 10.

 -- cgit-configuration parameter: integer summary-tags
     Specifies the number of tags to display in the repository ``summary'' view.

     Defaults to 10.

 -- cgit-configuration parameter: string strict-export
     Filename which, if specified, needs to be present within the repository for cgit to allow access to that repository.

     Defaults to "".

 -- cgit-configuration parameter: string virtual-root
     URL which, if specified, will be used as root for all cgit links.

     Defaults to "/".

 -- cgit-configuration parameter: repository-cgit-configuration-list repositories
     A list of repository-cgit-configuration records.

     Defaults to '().

     Available repository-cgit-configuration fields are:

      -- repository-cgit-configuration parameter: repo-list snapshots
          A mask of snapshot formats for this repo that cgit generates links for, restricted by the global snapshots setting.

          Defaults to '().

      -- repository-cgit-configuration parameter: repo-file-object source-filter
          Override the default source-filter.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string url
          The relative URL used to access the repository.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-file-object about-filter
          Override the default about-filter.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string branch-sort
          Flag which, when set to age, enables date ordering in the branch ref list, and when set to name enables ordering by branch name.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-list clone-url
          A list of URLs which can be used to clone repo.

          Defaults to '().

      -- repository-cgit-configuration parameter: repo-file-object commit-filter
          Override the default commit-filter.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string commit-sort
          Flag which, when set to date, enables strict date ordering in the commit log, and when set to topo enables strict topological ordering.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string defbranch
          The name of the default branch for this repository.  If no such branch exists in the repository, the first branch name (when sorted) is used as default instead.  By default branch pointed to by HEAD, or ``master'' if there is no suitable HEAD.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string desc
          The value to show as repository description.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string homepage
          The value to show as repository homepage.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-file-object email-filter
          Override the default email-filter.

          Defaults to "".

      -- repository-cgit-configuration parameter: maybe-repo-boolean enable-commit-graph?
          A flag which can be used to disable the global setting enable-commit-graph?.

          Defaults to disabled.

      -- repository-cgit-configuration parameter: maybe-repo-boolean enable-log-filecount?
          A flag which can be used to disable the global setting enable-log-filecount?.

          Defaults to disabled.

      -- repository-cgit-configuration parameter: maybe-repo-boolean enable-log-linecount?
          A flag which can be used to disable the global setting enable-log-linecount?.

          Defaults to disabled.

      -- repository-cgit-configuration parameter: maybe-repo-boolean enable-remote-branches?
          Flag which, when set to #t, will make cgit display remote branches in the summary and refs views.

          Defaults to disabled.

      -- repository-cgit-configuration parameter: maybe-repo-boolean enable-subject-links?
          A flag which can be used to override the global setting enable-subject-links?.

          Defaults to disabled.

      -- repository-cgit-configuration parameter: maybe-repo-boolean enable-html-serving?
          A flag which can be used to override the global setting enable-html-serving?.

          Defaults to disabled.

      -- repository-cgit-configuration parameter: repo-boolean hide?
          Flag which, when set to #t, hides the repository from the repository index.

          Defaults to #f.

      -- repository-cgit-configuration parameter: repo-boolean ignore?
          Flag which, when set to #t, ignores the repository.

          Defaults to #f.

      -- repository-cgit-configuration parameter: repo-file-object logo
          URL which specifies the source of an image which will be used as a logo on this repo’s pages.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string logo-link
          URL loaded when clicking on the cgit logo image.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-file-object owner-filter
          Override the default owner-filter.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string module-link
          Text which will be used as the formatstring for a hyperlink when a submodule is printed in a directory listing.  The arguments for the formatstring are the path and SHA1 of the submodule commit.

          Defaults to "".

      -- repository-cgit-configuration parameter: module-link-path module-link-path
          Text which will be used as the formatstring for a hyperlink when a submodule with the specified subdirectory path is printed in a directory listing.

          Defaults to '().

      -- repository-cgit-configuration parameter: repo-string max-stats
          Override the default maximum statistics period.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string name
          The value to show as repository name.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string owner
          A value used to identify the owner of the repository.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string path
          An absolute path to the repository directory.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string readme
          A path (relative to repo) which specifies a file to include verbatim as the ``About'' page for this repo.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-string section
          The name of the current repository section - all repositories defined after this option will inherit the current section name.

          Defaults to "".

      -- repository-cgit-configuration parameter: repo-list extra-options
          Extra options will be appended to cgitrc file.

          Defaults to '().

 -- cgit-configuration parameter: list extra-options
     Extra options will be appended to cgitrc file.

     Defaults to '().

However, it could be that you just want to get a cgitrc up and running.  In that case, you can pass an opaque-cgit-configuration as a record to cgit-service-type.  As its name indicates, an opaque configuration does not have easy reflective capabilities.

Available opaque-cgit-configuration fields are:

 -- opaque-cgit-configuration parameter: package cgit
     The cgit package.

 -- opaque-cgit-configuration parameter: string string
     The contents of the cgitrc, as a string.

For example, if your cgitrc is just the empty string, you could instantiate a cgit service like this:

     (service cgit-service-type
              (opaque-cgit-configuration
               (cgitrc "")))

Gitolite Service
................

Gitolite (https://gitolite.com/gitolite/) is a tool for hosting Git repositories on a central server.

Gitolite can handle multiple repositories and users, and supports flexible configuration of the permissions for the users on the repositories.

The following example will configure Gitolite using the default git user, and the provided SSH public key.

     (service gitolite-service-type
              (gitolite-configuration
                (admin-pubkey (plain-file
                                "yourname.pub"
                                "ssh-rsa AAAA... guix@example.com"))))

Gitolite is configured through a special admin repository which you can clone, for example, if you setup Gitolite on example.com, you would run the following command to clone the admin repository.

     git clone git@example.com:gitolite-admin

When the Gitolite service is activated, the provided admin-pubkey will be inserted in to the keydir directory in the gitolite-admin repository.  If this results in a change in the repository, it will be committed using the message ``gitolite setup by GNU Guix''.

 -- Data Type: gitolite-configuration
     Data type representing the configuration for gitolite-service-type.

     package (default: GITOLITE)
          Gitolite package to use.  There are optional Gitolite dependencies that are not included in the default package, such as Redis and git-annex. These features can be made available by using the make-gitolite procedure in the (gnu packages version-control) module to produce a variant of Gitolite with the desired additional dependencies.

          The following code returns a package in which the Redis and git-annex programs can be invoked by Gitolite's scripts:

               (use-modules (gnu packages databases)
                            (gnu packages haskell-apps)
                            (gnu packages version-control))
               (make-gitolite (list redis git-annex))

     user (default: GIT)
          User to use for Gitolite.  This will be user that you use when accessing Gitolite over SSH.

     group (default: GIT)
          Group to use for Gitolite.

     home-directory (default: "/VAR/LIB/GITOLITE")
          Directory in which to store the Gitolite configuration and repositories.

     rc-file (default: (GITOLITE-RC-FILE))
          A ``file-like'' object (see file-like objects), representing the configuration for Gitolite.

     admin-pubkey (default: #F)
          A ``file-like'' object (see file-like objects) used to setup Gitolite.  This will be inserted in to the keydir directory within the gitolite-admin repository.

          To specify the SSH key as a string, use the plain-file function.

               (plain-file "yourname.pub" "ssh-rsa AAAA... guix@example.com")

 -- Data Type: gitolite-rc-file
     Data type representing the Gitolite RC file.

     umask (default: #o0077)
          This controls the permissions Gitolite sets on the repositories and their contents.

          A value like #o0027 will give read access to the group used by Gitolite (by default: git).  This is necessary when using Gitolite with software like cgit or gitweb.

     local-code (default: "$rc{GL_ADMIN_BASE}/local")
          Allows you to add your own non-core programs, or even override the shipped ones with your own.

          Please supply the FULL path to this variable. By default, directory called "local" in your gitolite clone is used, providing the benefits of versioning them as well as making changes to them without having to log on to the server.

     unsafe-pattern (default: #f)
          An optional Perl regular expression for catching unsafe configurations in the configuration file.  See Gitolite's documentation (https://gitolite.com/gitolite/git-config.html#compensating-for-unsafe_patt) for more information.

          When the value is not #f, it should be a string containing a Perl regular expression, such as "[`~#\$\&()|;<>]", which is the default value used by gitolite.  It rejects any special character in configuration that might be interpreted by a shell, which is useful when sharing the administration burden with other people that do not otherwise have shell access on the server.

     git-config-keys (default: "")
          Gitolite allows you to set git config values using the config keyword.  This setting allows control over the config keys to accept.

     roles (default: '(("READERS" . 1) ("WRITERS" . )))
          Set the role names allowed to be used by users running the perms command.

     enable (default: '("help" "desc" "info" "perms" "writable" "ssh-authkeys" "git-config" "daemon" "gitweb"))
          This setting controls the commands and features to enable within Gitolite.

Gitile Service
..............

Gitile (https://git.lepiller.eu/gitile) is a Git forge for viewing public git repository contents from a web browser.

Gitile works best in collaboration with Gitolite, and will serve the public repositories from Gitolite by default.  The service should listen only on a local port, and a webserver should be configured to serve static resources. The gitile service provides an easy way to extend the Nginx service for that purpose (see NGINX).

The following example will configure Gitile to serve repositories from a custom location, with some default messages for the home page and the footers.

     (service gitile-service-type
              (gitile-configuration
                (repositories "/srv/git")
                (base-git-url "https://myweb.site/git")
                (index-title "My git repositories")
                (intro '((p "This is all my public work!")))
                (footer '((p "This is the end")))
                (nginx-server-block
                  (nginx-server-configuration
                    (ssl-certificate
                      "/etc/certs/myweb.site/fullchain.pem")
                    (ssl-certificate-key
                      "/etc/certs/myweb.site/privkey.pem")
                    (listen '("443 ssl http2" "[::]:443 ssl http2"))
                    (locations
                      (list
                        ;; Allow for https anonymous fetch on /git/ urls.
                        (git-http-nginx-location-configuration
                          (git-http-configuration
                            (uri-path "/git/")
                            (git-root "/var/lib/gitolite/repositories")))))))))

In addition to the configuration record, you should configure your git repositories to contain some optional information.  First, your public repositories need to contain the git-daemon-export-ok magic file that allows Git to export the repository.  Gitile uses the presence of this file to detect public repositories it should make accessible.  To do so with Gitolite for instance, modify your conf/gitolite.conf to include this in the repositories you want to make public:

     repo foo
         R = daemon

In addition, Gitile can read the repository configuration to display more information on the repository.  Gitile uses the gitweb namespace for its configuration.  As an example, you can use the following in your conf/gitolite.conf:

     repo foo
         R = daemon
         desc = A long description, optionally with <i>HTML</i>, shown on the index page
         config gitweb.name = The Foo Project
         config gitweb.synopsis = A short description, shown on the main page of the project

Do not forget to commit and push these changes once you are satisfied.  You may need to change your gitolite configuration to allow the previous configuration options to be set.  One way to do that is to add the following service definition:

     (service gitolite-service-type
               (gitolite-configuration
                 (admin-pubkey (local-file "key.pub"))
                 (rc-file
                   (gitolite-rc-file
                     (umask #o0027)
                     ;; Allow to set any configuration key
                     (git-config-keys ".*")
                     ;; Allow any text as a valid configuration value
                     (unsafe-patt "^$")))))

 -- Data Type: gitile-configuration
     Data type representing the configuration for gitile-service-type.

     package (default: GITILE)
          Gitile package to use.

     host (default: "localhost")
          The host on which gitile is listening.

     port (default: 8080)
          The port on which gitile is listening.

     database (default: "/var/lib/gitile/gitile-db.sql")
          The location of the database.

     repositories (default: "/var/lib/gitolite/repositories")
          The location of the repositories.  Note that only public repositories will be shown by Gitile.  To make a repository public, add an empty git-daemon-export-ok file at the root of that repository.

     base-git-url
          The base git url that will be used to show clone commands.

     index-title (default: "Index")
          The page title for the index page that lists all the available repositories.

     intro (default: '())
          The intro content, as a list of sxml expressions.  This is shown above the list of repositories, on the index page.

     footer (default: '())
          The footer content, as a list of sxml expressions.  This is shown on every page served by Gitile.

     nginx-server-block
          An nginx server block that will be extended and used as a reverse proxy by Gitile to serve its pages, and as a normal web server to serve its assets.

          You can use this block to add more custom URLs to your domain, such as a /git/ URL for anonymous clones, or serving any other files you would like to serve.

Game Services
-------------

Joycond service
...............

The joycond service allows the pairing of Nintendo joycon game controllers over Bluetooth. (see Desktop Services for setting up Bluetooth.)

 -- Data Type: joycond-configuration
     Data type representing the configuration of joycond.

     package (default: joycond)
          The joycond package to use.

 -- Variable: joycond-service-type
     Service type for the joycond service.

The Battle for Wesnoth Service
..............................

The Battle for Wesnoth (https://wesnoth.org) is a fantasy, turn based tactical strategy game, with several single player campaigns, and multiplayer games (both networked and local).

 -- Variable: wesnothd-service-type
     Service type for the wesnothd service.  Its value must be a wesnothd-configuration object.  To run wesnothd in the default configuration, instantiate it as:

          (service wesnothd-service-type)

 -- Data Type: wesnothd-configuration
     Data type representing the configuration of wesnothd.

     package (default: wesnoth-server)
          The wesnoth server package to use.

     port (default: 15000)
          The port to bind the server to.

PAM Mount Service
-----------------

The (gnu services pam-mount) module provides a service allowing users to mount volumes when they log in.  It should be able to mount any volume format supported by the system.

 -- Variable: pam-mount-service-type
     Service type for PAM Mount support.

 -- Data Type: pam-mount-configuration
     Data type representing the configuration of PAM Mount.

     It takes the following parameters:

     rules
          The configuration rules that will be used to generate /etc/security/pam_mount.conf.xml.

          The configuration rules are SXML elements (see SXML (GNU Guile Reference Manual)), and the default ones don't mount anything for anyone at login:

               `((debug (@ (enable "0")))
                 (mntoptions (@ (allow ,(string-join
                                         '("nosuid" "nodev" "loop"
                                           "encryption" "fsck" "nonempty"
                                           "allow_root" "allow_other")
                                         ","))))
                 (mntoptions (@ (require "nosuid,nodev")))
                 (logout (@ (wait "0")
                            (hup "0")
                            (term "no")
                            (kill "no")))
                 (mkmountpoint (@ (enable "1")
                                  (remove "true"))))

          Some volume elements must be added to automatically mount volumes at login.  Here's an example allowing the user alice to mount her encrypted HOME directory and allowing the user bob to mount the partition where he stores his data:

               (define pam-mount-rules
               `((debug (@ (enable "0")))
                           (volume (@ (user "alice")
                                      (fstype "crypt")
                                      (path "/dev/sda2")
                                      (mountpoint "/home/alice")))
                           (volume (@ (user "bob")
                                      (fstype "auto")
                                      (path "/dev/sdb3")
                                      (mountpoint "/home/bob/data")
                                      (options "defaults,autodefrag,compress")))
                           (mntoptions (@ (allow ,(string-join
                                                   '("nosuid" "nodev" "loop"
                                                     "encryption" "fsck" "nonempty"
                                                     "allow_root" "allow_other")
                                                   ","))))
                           (mntoptions (@ (require "nosuid,nodev")))
                           (logout (@ (wait "0")
                                      (hup "0")
                                      (term "no")
                                      (kill "no")))
                           (mkmountpoint (@ (enable "1")
                                            (remove "true")))))

               (service pam-mount-service-type
                        (pam-mount-configuration
                          (rules pam-mount-rules)))

          The complete list of possible options can be found in the man page for pam_mount.conf (http://pam-mount.sourceforge.net/pam_mount.conf.5.html).

PAM Mount Volume Service
------------------------

PAM mount volumes are automatically mounted at login by the PAM login service according to a set of per-volume rules.  Because they are mounted by PAM the password entered during login may be used directly to mount authenticated volumes, such as cifs, using the same credentials.

These volumes will be added in addition to any volumes directly specified in pam-mount-rules.

Here is an example of a rule which will mount a remote CIFS share from //remote-server/share into a sub-directory of /shares named after the user logging in:

     (simple-service 'pam-mount-remote-share pam-mount-volume-service-type
                     (list (pam-mount-volume
                            (secondary-group "users")
                            (file-system-type "cifs")
                            (server "remote-server")
                            (file-name "share")
                            (mount-point "/shares/%(USER)")
                            (options "nosuid,nodev,seal,cifsacl"))))

 -- Data Type: pam-mount-volume-service-type
     Configuration for a single volume to be mounted.  Any fields not specified will be omitted from the run-time PAM configuration.  See the man page (http://pam-mount.sourceforge.net/pam_mount.conf.5.html) for the default values when unspecified.

     user-name (type: maybe-string)
          Mount the volume for the given user.

     user-id (type: maybe-integer-or-range)
          Mount the volume for the user with this ID.  This field may also be specified as a pair of (start . end) indicating a range of user IDs for whom to mount the volume.

     primary-group (type: maybe-string)
          Mount the volume for users with this primary group name.

     group-id (type: maybe-integer-or-range)
          Mount the volume for the users with this primary group ID.  This field may also be specified as a cons cell of (start . end) indicating a range of group ids for whom to mount the volume.

     secondary-group (type: maybe-string)
          Mount the volume for users who are members of this group as either a primary or secondary group.

     file-system-type (type: maybe-string)
          The file system type for the volume being mounted (e.g., cifs)

     no-mount-as-root? (type: maybe-boolean)
          Whether or not to mount the volume with root privileges.  This is normally disabled, but may be enabled for mounts of type fuse, or other user-level mounts.

     server (type: maybe-string)
          The name of the remote server to mount the volume from, when necessary.

     file-name (type: maybe-string)
          The location of the volume, either local or remote, depending on the file-system-type.

     mount-point (type: maybe-string)
          Where to mount the volume in the local file-system.  This may be set to ~ to indicate the home directory of the user logging in.  If this field is omitted then /etc/fstab is consulted for the mount destination.

     options (type: maybe-string)
          The options to be passed as-is to the underlying mount program.

     ssh? (type: maybe-boolean)
          Enable this option to pass the login password to SSH for use with mounts involving SSH (e.g., sshfs).

     cipher (type: maybe-string)
          Cryptsetup cipher name for the volume.  To be used with the crypt file-system-type.

     file-system-key-cipher (type: maybe-string)
          Cipher name used by the target volume.

     file-system-key-hash (type: maybe-string)
          SSL hash name used by the target volume.

     file-system-key-file-name (type: maybe-string)
          File name of the file system key for the target volume.

Guix Services
-------------

Build Farm Front-End (BFFE)
...........................

The Build Farm Front-End (https://git.cbaines.net/guix/bffe/) assists with building Guix packages in bulk.  It's responsible for submitting builds and displaying the status of the build farm.

 -- Variable: bffe-service-type
     Service type for the Build Farm Front-End.  Its value must be a bffe-configuration object.

 -- Data Type: bffe-configuration
     Data type representing the configuration of the Build Farm Front-End.

     package (default: bffe)
          The Build Farm Front-End package to use.

     user (default: "bffe")
          The system user to run the service as.

     group (default: "bffe")
          The system group to run the service as.

     arguments
          A list of arguments to the Build Farm Front-End.  These are passed to the run-bffe-service procedure when starting the service.

          For example, the following value directs the Build Farm Front-End to submit builds for derivations available from data.guix.gnu.org to the Build Coordinator instance assumed to be running on the same machine.

               (list
                #:build
                (list
                 (build-from-guix-data-service
                  (data-service-url "https://data.guix.gnu.org")
                  (build-coordinator-url "http://127.0.0.1:8746")
                  (branches '("master"))
                  (systems '("x86_64-linux" "i686-linux"))
                  (systems-and-targets
                   (map (lambda (target)
                          (cons "x86_64-linux" target))
                        '("aarch64-linux-gnu"
                          "i586-pc-gnu")))
                  (build-priority (const 0))))
                #:web-server-args
                '(#:event-source "https://example.com"
                  #:controller-args
                  (#:title "example.com build farm")))

     extra-environment-variables (default: '())
          Extra environment variables to set via the shepherd service.

Guix Build Coordinator
......................

The Guix Build Coordinator (https://git.cbaines.net/guix/build-coordinator/) aids in distributing derivation builds among machines running an agent.  The build daemon is still used to build the derivations, but the Guix Build Coordinator manages allocating builds and working with the results.

The Guix Build Coordinator consists of one coordinator, and one or more connected agent processes.  The coordinator process handles clients submitting builds, and allocating builds to agents.  The agent processes talk to a build daemon to actually perform the builds, then send the results back to the coordinator.

There is a script to run the coordinator component of the Guix Build Coordinator, but the Guix service uses a custom Guile script instead, to provide better integration with G-expressions used in the configuration.

 -- Variable: guix-build-coordinator-service-type
     Service type for the Guix Build Coordinator.  Its value must be a guix-build-coordinator-configuration object.

 -- Data Type: guix-build-coordinator-configuration
     Data type representing the configuration of the Guix Build Coordinator.

     package (default: guix-build-coordinator)
          The Guix Build Coordinator package to use.

     user (default: "guix-build-coordinator")
          The system user to run the service as.

     group (default: "guix-build-coordinator")
          The system group to run the service as.

     database-uri-string (default: "sqlite:///var/lib/guix-build-coordinator/guix_build_coordinator.db")
          The URI to use for the database.

     agent-communication-uri (default: "http://0.0.0.0:8745")
          The URI describing how to listen to requests from agent processes.

     client-communication-uri (default: "http://127.0.0.1:8746")
          The URI describing how to listen to requests from clients.  The client API allows submitting builds and currently isn't authenticated, so take care when configuring this value.

     allocation-strategy (default: #~basic-build-allocation-strategy)
          A G-expression for the allocation strategy to be used.  This is a procedure that takes the datastore as an argument and populates the allocation plan in the database.

     hooks (default: '())
          An association list of hooks.  These provide a way to execute arbitrary code upon certain events, like a build result being processed.

     parallel-hooks (default: '())
          Hooks can be configured to run in parallel.  This parameter is an association list of hooks to do in parallel, where the key is the symbol for the hook and the value is the number of threads to run.

     guile (default: guile-3.0-latest)
          The Guile package with which to run the Guix Build Coordinator.

     extra-environment-variables (default: '())
          Extra environment variables to set via the shepherd service.

 -- Variable: guix-build-coordinator-agent-service-type
     Service type for a Guix Build Coordinator agent.  Its value must be a guix-build-coordinator-agent-configuration object.

 -- Data Type: guix-build-coordinator-agent-configuration
     Data type representing the configuration a Guix Build Coordinator agent.

     package (default: guix-build-coordinator/agent-only)
          The Guix Build Coordinator package to use.

     user (default: "guix-build-coordinator-agent")
          The system user to run the service as.

     coordinator (default: "http://localhost:8745")
          The URI to use when connecting to the coordinator.

     authentication
          Record describing how this agent should authenticate with the coordinator.  Possible record types are described below.

     systems (default: #f)
          The systems for which this agent should fetch builds.  The agent process will use the current system it's running on as the default.

     max-parallel-builds (default: 1)
          The number of builds to perform in parallel.

     max-parallel-uploads (default: 1)
          The number of uploads to perform in parallel.

     max-allocated-builds (default: #f)
          The maximum number of builds this agent can be allocated.

     max-1min-load-average (default: #f)
          Load average value to look at when considering starting new builds, if the 1 minute load average exceeds this value, the agent will wait before starting new builds.

          This will be unspecified if the value is #f, and the agent will use the number of cores reported by the system as the max 1 minute load average.

     derivation-substitute-urls (default: #f)
          URLs from which to attempt to fetch substitutes for derivations, if the derivations aren't already available.

     non-derivation-substitute-urls (default: #f)
          URLs from which to attempt to fetch substitutes for build inputs, if the input store items aren't already available.

 -- Data Type: guix-build-coordinator-agent-password-auth
     Data type representing an agent authenticating with a coordinator via a UUID and password.

     uuid
          The UUID of the agent.  This should be generated by the coordinator process, stored in the coordinator database, and used by the intended agent.

     password
          The password to use when connecting to the coordinator.

 -- Data Type: guix-build-coordinator-agent-password-file-auth
     Data type representing an agent authenticating with a coordinator via a UUID and password read from a file.

     uuid
          The UUID of the agent.  This should be generated by the coordinator process, stored in the coordinator database, and used by the intended agent.

     password-file
          A file containing the password to use when connecting to the coordinator.

 -- Data Type: guix-build-coordinator-agent-dynamic-auth
     Data type representing an agent authenticating with a coordinator via a dynamic auth token and agent name.

     agent-name
          Name of an agent, this is used to match up to an existing entry in the database if there is one.  When no existing entry is found, a new entry is automatically added.

     token
          Dynamic auth token, this is created and stored in the coordinator database, and is used by the agent to authenticate.

 -- Data Type: guix-build-coordinator-agent-dynamic-auth-with-file
     Data type representing an agent authenticating with a coordinator via a dynamic auth token read from a file and agent name.

     agent-name
          Name of an agent, this is used to match up to an existing entry in the database if there is one.  When no existing entry is found, a new entry is automatically added.

     token-file
          File containing the dynamic auth token, this is created and stored in the coordinator database, and is used by the agent to authenticate.

Guix Data Service
.................

The Guix Data Service (http://data.guix.gnu.org) processes, stores and provides data about GNU Guix.  This includes information about packages, derivations and lint warnings.

The data is stored in a PostgreSQL database, and available through a web interface.

 -- Variable: guix-data-service-type
     Service type for the Guix Data Service.  Its value must be a guix-data-service-configuration object.  The service optionally extends the getmail service, as the guix-commits mailing list is used to find out about changes in the Guix git repository.

 -- Data Type: guix-data-service-configuration
     Data type representing the configuration of the Guix Data Service.

     package (default: guix-data-service)
          The Guix Data Service package to use.

     user (default: "guix-data-service")
          The system user to run the service as.

     group (default: "guix-data-service")
          The system group to run the service as.

     port (default: 8765)
          The port to bind the web service to.

     host (default: "127.0.0.1")
          The host to bind the web service to.

     getmail-idle-mailboxes (default: #f)
          If set, this is the list of mailboxes that the getmail service will be configured to listen to.

     commits-getmail-retriever-configuration (default: #f)
          If set, this is the getmail-retriever-configuration object with which to configure getmail to fetch mail from the guix-commits mailing list.

     extra-options (default: '())
          Extra command line options for guix-data-service.

     extra-process-jobs-options (default: '())
          Extra command line options for guix-data-service-process-jobs.

Nar Herder
..........

The Nar Herder (https://git.cbaines.net/guix/nar-herder/about/) is a utility for managing a collection of nars.

 -- Variable: nar-herder-type
     Service type for the Guix Data Service.  Its value must be a nar-herder-configuration object.  The service optionally extends the getmail service, as the guix-commits mailing list is used to find out about changes in the Guix git repository.

 -- Data Type: nar-herder-configuration
     Data type representing the configuration of the Guix Data Service.

     package (default: nar-herder)
          The Nar Herder package to use.

     user (default: "nar-herder")
          The system user to run the service as.

     group (default: "nar-herder")
          The system group to run the service as.

     port (default: 8734)
          The port to bind the server to.

     host (default: "127.0.0.1")
          The host to bind the server to.

     mirror (default: #f)
          Optional URL of the other Nar Herder instance which should be mirrored. This means that this Nar Herder instance will download it's database, and keep it up to date.

     database (default: "/var/lib/nar-herder/nar_herder.db")
          Location for the database.  If this Nar Herder instance is mirroring another, the database will be downloaded if it doesn't exist.  If this Nar Herder instance isn't mirroring another, an empty database will be created.

     database-dump (default: "/var/lib/nar-herder/nar_herder_dump.db")
          Location of the database dump.  This is created and regularly updated by taking a copy of the database.  This is the version of the database that is available to download.

     storage (default: #f)
          Optional location in which to store nars.

     storage-limit (default: "none")
          Limit in bytes for the nars stored in the storage location.  This can also be set to ``none'' so that there is no limit.

          When the storage location exceeds this size, nars are removed according to the nar removal criteria.

     storage-nar-removal-criteria (default: '())
          Criteria used to remove nars from the storage location.  These are used in conjunction with the storage limit.

          When the storage location exceeds the storage limit size, nars will be checked against the nar removal criteria and if any of the criteria match, they will be removed.  This will continue until the storage location is below the storage limit size.

          Each criteria is specified by a string, then an equals sign, then another string. Currently, only one criteria is supported, checking if a nar is stored on another Nar Herder instance.

     ttl (default: #f)
          Produce Cache-Control HTTP headers that advertise a time-to-live (TTL) of TTL.  TTL must denote a duration: 5d means 5 days, 1m means 1 month, and so on.

          This allows the user's Guix to keep substitute information in cache for TTL.

     negative-ttl (default: #f)
          Similarly produce Cache-Control HTTP headers to advertise the time-to-live (TTL) of negative lookups---missing store items, for which the HTTP 404 code is returned.  By default, no negative TTL is advertised.

     log-level (default: 'DEBUG)
          Log level to use, specify a log level like 'INFO to stop logging individual requests.

     cached-compressions (default: '())
          Activate generating cached nars with different compression details from the stored nars.  This is a list of nar-herder-cached-compression-configuration records.

     min-uses (default: 3)
          When cached-compressions are enabled, generate cached nars when at least this number of requests are made for a nar.

     workers (default: 2)
          Number of cached nars to generate at a time.

     nar-source (default: #f)
          Location to fetch nars from when computing cached compressions.  By default, the storage location will be used.

     extra-environment-variables (default: '())
          Extra environment variables to set via the shepherd service.

 -- Data Type: nar-herder-cached-compression-configuration
     Data type representing the cached compression configuration.

     type
          Type of compression to use, e.g. 'zstd.

     workers (default: #f)
          Level of the compression to use.

     directory (default: #f)
          Location to store the cached nars.  If unspecified, they will be stored in /var/cache/nar-herder/nar/TYPE.

     directory-max-size (default: #f)
          Maximum size in bytes of the directory.

Linux Services
--------------

Early OOM Service
.................

Early OOM (https://github.com/rfjakob/earlyoom), also known as Earlyoom, is a minimalist out of memory (OOM) daemon that runs in user space and provides a more responsive and configurable alternative to the in-kernel OOM killer.  It is useful to prevent the system from becoming unresponsive when it runs out of memory.

 -- Variable: earlyoom-service-type
     The service type for running earlyoom, the Early OOM daemon. Its value must be a earlyoom-configuration object, described below.  The service can be instantiated in its default configuration with:

          (service earlyoom-service-type)

 -- Data Type: earlyoom-configuration
     This is the configuration record for the earlyoom-service-type.

     earlyoom (default: EARLYOOM)
          The Earlyoom package to use.

     minimum-available-memory (default: 10)
          The threshold for the minimum available memory, in percentages.

     minimum-free-swap (default: 10)
          The threshold for the minimum free swap memory, in percentages.

     prefer-regexp (default: #f)
          A regular expression (as a string) to match the names of the processes that should be preferably killed.

     avoid-regexp (default: #f)
          A regular expression (as a string) to match the names of the processes that should not be killed.

     memory-report-interval (default: 0)
          The interval in seconds at which a memory report is printed.  It is disabled by default.

     ignore-positive-oom-score-adj? (default: #f)
          A boolean indicating whether the positive adjustments set in /proc/*/oom_score_adj should be ignored.

     show-debug-messages? (default: #f)
          A boolean indicating whether debug messages should be printed.  The logs are saved at /var/log/earlyoom.log.

     send-notification-command (default: #f)
          This can be used to provide a custom command used for sending notifications.

fstrim Service
..............

The command fstrim can be used to discard (or trim) unused blocks on a mounted file system.

     Running fstrim frequently, or even using mount -o discard, might negatively affect the lifetime of poor-quality SSD devices.  For most desktop and server systems a sufficient trimming frequency is once a week.  Note that not all devices support a queued trim, so each trim command incurs a performance penalty on whatever else might be trying to use the disk at the time.

 -- Variable: fstrim-service-type
     Type for a service that periodically runs fstrim, whose value must be an <fstrim-configuration> object.  The service can be instantiated in its default configuration with:

          (service fstrim-service-type)

 -- Data Type: fstrim-configuration
     Available fstrim-configuration fields are:

     package (default: util-linux) (type: file-like)
          The package providing the fstrim command.

     schedule (default: "0 0 * * 0") (type: mcron-time)
          Schedule for launching fstrim.  This can be a procedure, a list or a string.  For additional information, see Job specification (the mcron manual).  By default this is set to run weekly on Sunday at 00:00.

     listed-in (default: '("/etc/fstab" "/proc/self/mountinfo")) (type: maybe-list-of-strings)
          List of files in fstab or kernel mountinfo format.  All missing or empty files are silently ignored.  The evaluation of the list stops after the first non-empty file.  File systems with X-fstrim.notrim mount option in fstab are skipped.

     verbose? (default: #t) (type: boolean)
          Verbose execution.

     quiet-unsupported? (default: #t) (type: boolean)
          Suppress error messages if trim operation (ioctl) is unsupported.

     extra-arguments (type: maybe-list-of-strings)
          Extra options to append to fstrim (run man fstrim for more information).

Kernel Module Loader Service
............................

The kernel module loader service allows one to load loadable kernel modules at boot.  This is especially useful for modules that don't autoload and need to be manually loaded, as is the case with ddcci.

 -- Variable: kernel-module-loader-service-type
     The service type for loading loadable kernel modules at boot with modprobe.  Its value must be a list of strings representing module names.  For example loading the drivers provided by ddcci-driver-linux, in debugging mode by passing some module parameters, can be done as follow:

          (use-modules (gnu) (gnu services))
          (use-package-modules linux)
          (use-service-modules linux)

          (define ddcci-config
            (plain-file "ddcci.conf"
                        "options ddcci dyndbg delay=120"))

          (operating-system
            ...
            (services (cons* (service kernel-module-loader-service-type
                                      '("ddcci" "ddcci_backlight"))
                             (simple-service 'ddcci-config etc-service-type
                                             (list `("modprobe.d/ddcci.conf"
                                                     ,ddcci-config)))
                             %base-services))
            (kernel-loadable-modules (list ddcci-driver-linux)))

Cachefilesd Service
...................

The Cachefilesd service starts a daemon that caches network file system data locally.  It is especially useful for NFS and AFS shares, where it reduces latencies for repeated access when reading files.

The daemon can be configured as follows:

     (service cachefilesd-service-type
              (cachefilesd-configuration
                (cache-directory "/var/cache/fscache")))

 -- Variable: cachefilesd-service-type
     The service type for starting cachefilesd.  The value for this service type is a cachefilesd-configuration, whose only required field is CACHE-DIRECTORY.

 -- Data Type: cachefilesd-configuration
     Available cachefilesd-configuration fields are:

     cachefilesd (default: cachefilesd) (type: file-like)
          The cachefilesd package to use.

     debug-output? (default: #f) (type: boolean)
          Print debugging output to stderr.

     use-syslog? (default: #t) (type: boolean)
          Log to syslog facility instead of stdout.

     scan? (default: #t) (type: boolean)
          Scan for cachable objects.

     cache-directory (type: maybe-string)
          Location of the cache directory.

     cache-name (default: "CacheFiles") (type: maybe-string)
          Name of cache (keep unique).

     security-context (type: maybe-string)
          SELinux security context.

     pause-culling-for-block-percentage (default: 7) (type: maybe-non-negative-integer)
          Pause culling when available blocks exceed this percentage.

     pause-culling-for-file-percentage (default: 7) (type: maybe-non-negative-integer)
          Pause culling when available files exceed this percentage.

     resume-culling-for-block-percentage (default: 5) (type: maybe-non-negative-integer)
          Start culling when available blocks drop below this percentage.

     resume-culling-for-file-percentage (default: 5) (type: maybe-non-negative-integer)
          Start culling when available files drop below this percentage.

     pause-caching-for-block-percentage (default: 1) (type: maybe-non-negative-integer)
          Pause further allocations when available blocks drop below this percentage.

     pause-caching-for-file-percentage (default: 1) (type: maybe-non-negative-integer)
          Pause further allocations when available files drop below this percentage.

     log2-table-size (default: 12) (type: maybe-non-negative-integer)
          Size of tables holding cullable objects in logarithm of base 2.

     cull? (default: #t) (type: boolean)
          Create free space by culling (consumes system load).

     trace-function-entry-in-kernel-module? (default: #f) (type: boolean)
          Trace function entry in the kernel module (for debugging).

     trace-function-exit-in-kernel-module? (default: #f) (type: boolean)
          Trace function exit in the kernel module (for debugging).

     trace-internal-checkpoints-in-kernel-module? (default: #f) (type: boolean)
          Trace internal checkpoints in the kernel module (for debugging).

Rasdaemon Service
.................

The Rasdaemon service provides a daemon which monitors platform RAS (Reliability, Availability, and Serviceability) reports from Linux kernel trace events, logging them to syslogd.

Reliability, Availability and Serviceability is a concept used on servers meant to measure their robustness.

Relability is the probability that a system will produce correct outputs:

  * Generally measured as Mean Time Between Failures (MTBF), and

  * Enhanced by features that help to avoid, detect and repair hardware faults

Availability is the probability that a system is operational at a given time:

  * Generally measured as a percentage of downtime per a period of time, and

  * Often uses mechanisms to detect and correct hardware faults in runtime.

Serviceability is the simplicity and speed with which a system can be repaired or maintained:

  * Generally measured on Mean Time Between Repair (MTBR).

Among the monitoring measures, the most usual ones include:

  * CPU – detect errors at instruction execution and at L1/L2/L3 caches;

  * Memory – add error correction logic (ECC) to detect and correct errors;

  * I/O – add CRC checksums for transferred data;

  * Storage – RAID, journal file systems, checksums, Self-Monitoring, Analysis and Reporting Technology (SMART).

By monitoring the number of occurrences of error detections, it is possible to identify if the probability of hardware errors is increasing, and, on such case, do a preventive maintenance to replace a degraded component while those errors are correctable.

For detailed information about the types of error events gathered and how to make sense of them, see the kernel administrator's guide at https://www.kernel.org/doc/html/latest/admin-guide/ras.html.

 -- Variable: rasdaemon-service-type
     Service type for the rasdaemon service.  It accepts a rasdaemon-configuration object.  Instantiating like

          (service rasdaemon-service-type)

     will load with a default configuration, which monitors all events and logs to syslogd.

 -- Data Type: rasdaemon-configuration
     The data type representing the configuration of rasdaemon.

     record? (default: #f)

          A boolean indicating whether to record the events in an SQLite database.  This provides a more structured access to the information contained in the log file. The database location is hard-coded to /var/lib/rasdaemon/ras-mc_event.db.

Zram Device Service
...................

The Zram device service provides a compressed swap device in system memory.  The Linux Kernel documentation has more information about zram (https://www.kernel.org/doc/html/latest/admin-guide/blockdev/zram.html) devices.

 -- Variable: zram-device-service-type
     This service creates the zram block device, formats it as swap and enables it as a swap device.  The service's value is a zram-device-configuration record.

      -- Data Type: zram-device-configuration
          This is the data type representing the configuration for the zram-device service.

          size (default "1G")
               This is the amount of space you wish to provide for the zram device.  It accepts a string and can be a number of bytes or use a suffix, eg.: "512M" or 1024000.

          compression-algorithm (default 'lzo)
               This is the compression algorithm you wish to use.  It is difficult to list all the possible compression options, but common ones supported by Guix's Linux Libre Kernel include 'lzo, 'lz4 and 'zstd.

          memory-limit (default 0)
               This is the maximum amount of memory which the zram device can use. Setting it to '0' disables the limit.  While it is generally expected that compression will be 2:1, it is possible that uncompressable data can be written to swap and this is a method to limit how much memory can be used.  It accepts a string and can be a number of bytes or use a suffix, eg.: "2G".

          priority (default #f)
               This is the priority of the swap device created from the zram device. See Swap Space for a description of swap priorities.  You might want to set a specific priority for the zram device, otherwise it could end up not being used much for the reasons described there.

Hurd Services
-------------

 -- Variable: hurd-console-service-type
     This service starts the fancy VGA console client on the Hurd.

     The service's value is a hurd-console-configuration record.

 -- Data Type: hurd-console-configuration
     This is the data type representing the configuration for the hurd-console-service.

     hurd (default: HURD)
          The Hurd package to use.

 -- Variable: hurd-getty-service-type
     This service starts a tty using the Hurd getty program.

     The service's value is a hurd-getty-configuration record.

 -- Data Type: hurd-getty-configuration
     This is the data type representing the configuration for the hurd-getty-service.

     hurd (default: HURD)
          The Hurd package to use.

     tty
          The name of the console this Getty runs on---e.g., "tty1".

     baud-rate (default: 38400)
          An integer specifying the baud rate of the tty.

Miscellaneous Services
----------------------

Fingerprint Service
...................

The (gnu services authentication) module provides a DBus service to read and identify fingerprints via a fingerprint sensor.

 -- Variable: fprintd-service-type
     The service type for fprintd, which provides the fingerprint reading capability.

          (service fprintd-service-type)

System Control Service
......................

The (gnu services sysctl) provides a service to configure kernel parameters at boot.

 -- Variable: sysctl-service-type
     The service type for sysctl, which modifies kernel parameters under /proc/sys/.  To enable IPv4 forwarding, it can be instantiated as:

          (service sysctl-service-type
                   (sysctl-configuration
                     (settings '(("net.ipv4.ip_forward" . "1")))))

     Since sysctl-service-type is used in the default lists of services, %base-services and %desktop-services, you can use modify-services to change its configuration and add the kernel parameters that you want (see modify-services).

          (modify-services %base-services
            (sysctl-service-type config =>
                                 (sysctl-configuration
                                   (settings (append '(("net.ipv4.ip_forward" . "1"))
                                                     %default-sysctl-settings)))))

 -- Data Type: sysctl-configuration
     The data type representing the configuration of sysctl.

     sysctl (default: (file-append procps "/sbin/sysctl")
          The sysctl executable to use.

     settings (default: %default-sysctl-settings)
          An association list specifies kernel parameters and their values.

 -- Variable: %default-sysctl-settings
     An association list specifying the default sysctl parameters on Guix System.

PC/SC Smart Card Daemon Service
...............................

The (gnu services security-token) module provides the following service to run pcscd, the PC/SC Smart Card Daemon.  pcscd is the daemon program for pcsc-lite and the MuscleCard framework.  It is a resource manager that coordinates communications with smart card readers, smart cards and cryptographic tokens that are connected to the system.

 -- Variable: pcscd-service-type
     Service type for the pcscd service.  Its value must be a pcscd-configuration object.  To run pcscd in the default configuration, instantiate it as:

          (service pcscd-service-type)

 -- Data Type: pcscd-configuration
     The data type representing the configuration of pcscd.

     pcsc-lite (default: pcsc-lite)
          The pcsc-lite package that provides pcscd.

     usb-drivers (default: (list ccid))
          List of packages that provide USB drivers to pcscd.  Drivers are expected to be under pcsc/drivers in the store directory of the package.

LIRC Service
............

The (gnu services lirc) module provides the following service.

 -- Variable: lirc-service-type
     Type for a service that runs LIRC (http://www.lirc.org), a daemon that decodes infrared signals from remote controls.

     The value for this service is a <lirc-configuration> object.

 -- Data Type: lirc-configuration
     Data type representing the configuration of lircd.

     lirc (default: lirc) (type: file-like)
          Package object for lirc.

     device (default: #f) (type: string)
     driver (default: #f) (type: string)
     config-file (default: #f) (type: string-or-file-like)
          TODO.  See lircd manual for details.

     extra-options (default: '()) (type: list-of-string)
          Additional command-line options to pass to lircd.

SPICE Service
.............

The (gnu services spice) module provides the following service.

 -- Variable: spice-vdagent-service-type
     Type of the service that runs VDAGENT (https://www.spice-space.org), a daemon that enables sharing the clipboard with a vm and setting the guest display resolution when the graphical console window resizes.

 -- Data Type: spice-vdagent-configuration
     Data type representing the configuration of spice-vdagent-service-type.

     spice-vdagent (default: spice-vdagent) (type: file-like)
          Package object for VDAGENT.

inputattach Service
...................

The inputattach (https://linuxwacom.github.io/) service allows you to use input devices such as Wacom tablets, touchscreens, or joysticks with the Xorg display server.

 -- Variable: inputattach-service-type
     Type of a service that runs inputattach on a device and dispatches events from it.

 -- Data Type: inputattach-configuration

     device-type (default: "wacom")
          The type of device to connect to.  Run inputattach --help, from the inputattach package, to see the list of supported device types.

     device (default: "/dev/ttyS0")
          The device file to connect to the device.

     baud-rate (default: #f)
          Baud rate to use for the serial connection. Should be a number or #f.

     log-file (default: #f)
          If true, this must be the name of a file to log messages to.

Dictionary Service
..................

The (gnu services dict) module provides the following service:

 -- Variable: dicod-service-type
     This is the type of the service that runs the dicod daemon, an implementation of DICT server (see Dicod (GNU Dico Manual)).

     You can add open localhost to your ~/.dico file to make localhost the default server for dico client (see Initialization File (GNU Dico Manual)).

          This service is also available for Guix Home, where it runs directly with your user privileges (see home-dicod-service-type).

 -- Data Type: dicod-configuration
     Data type representing the configuration of dicod.

     dico (default: DICO)
          Package object of the GNU Dico dictionary server.

     interfaces (default: '("LOCALHOST"))
          This is the list of IP addresses and ports and possibly socket file names to listen to (see listen directive (GNU Dico Manual)).

     handlers (default: '())
          List of <dicod-handler> objects denoting handlers (module instances).

     databases (default: (LIST %DICOD-DATABASE:GCIDE))
          List of <dicod-database> objects denoting dictionaries to be served.

 -- Data Type: dicod-handler
     Data type representing a dictionary handler (module instance).

     name
          Name of the handler (module instance).

     module (default: #F)
          Name of the dicod module of the handler (instance).  If it is #f, the module has the same name as the handler. (see Modules (GNU Dico Manual)).

     options
          List of strings or gexps representing the arguments for the module handler

 -- Data Type: dicod-database
     Data type representing a dictionary database.

     name
          Name of the database, will be used in DICT commands.

     handler
          Name of the dicod handler (module instance) used by this database (see Handlers (GNU Dico Manual)).

     complex? (default: #F)
          Whether the database configuration complex.  The complex configuration will need a corresponding <dicod-handler> object, otherwise not.

     options
          List of strings or gexps representing the arguments for the database (see Databases (GNU Dico Manual)).

 -- Variable: %dicod-database:gcide
     A <dicod-database> object serving the GNU Collaborative International Dictionary of English using the gcide package.

The following is an example dicod-service-type configuration.

     (service dicod-service-type
              (dicod-configuration
               (handlers (list
                          (dicod-handler
                           (name "wordnet")
                           (module "wordnet")
                           (options
                            (list #~(string-append "wnhome=" #$wordnet))))))
               (databases (list
                           (dicod-database
                            (name "wordnet")
                            (complex? #t)
                            (handler "wordnet"))
                           %dicod-database:gcide))))

Docker Service
..............

The (gnu services docker) module provides the following services.

 -- Variable: docker-service-type

     This is the type of the service that runs Docker (https://www.docker.com), a daemon that can execute application bundles (sometimes referred to as ``containers'') in isolated environments.

 -- Data Type: docker-configuration
     This is the data type representing the configuration of Docker and Containerd.

     docker (default: docker)
          The Docker daemon package to use.

     docker-cli (default: docker-cli)
          The Docker client package to use.

     containerd (default: CONTAINERD)
          The Containerd package to use.

     proxy (default DOCKER-LIBNETWORK-CMD-PROXY)
          The Docker user-land networking proxy package to use.

     enable-proxy? (default #t)
          Enable or disable the use of the Docker user-land networking proxy.

     debug? (default #f)
          Enable or disable debug output.

     enable-iptables? (default #t)
          Enable or disable the addition of iptables rules.

     environment-variables (default: '())
          List of environment variables to set for dockerd.

          This must be a list of strings where each string has the form KEY=VALUE as in this example:

               (list "LANGUAGE=eo:ca:eu"
                     "TMPDIR=/tmp/dockerd")

     config-file (type: maybe-file-like)
          JSON configuration file pass to dockerd.

 -- Variable: singularity-service-type
     This is the type of the service that allows you to run Singularity (https://www.sylabs.io/singularity/), a Docker-style tool to create and run application bundles (aka. ``containers'').  The value for this service is the Singularity package to use.

     The service does not install a daemon; instead, it installs helper programs as setuid-root (see Setuid Programs) such that unprivileged users can invoke singularity run and similar commands.

OCI backed services
...................

Should you wish to manage your Docker containers with the same consistent interface you use for your other Shepherd services, OCI-CONTAINER-SERVICE-TYPE is the tool to use: given an Open Container Initiative (OCI) container image, it will run it in a Shepherd service.  One example where this is useful: it lets you run services that are available as Docker/OCI images but not yet packaged for Guix.

 -- Variable: oci-container-service-type

     This is a thin wrapper around Docker's CLI that executes OCI images backed processes as Shepherd Services.

          (service oci-container-service-type
                   (list
                    (oci-container-configuration
                     (image "prom/prometheus")
                     (network "host")
                     (ports
                       '(("9000" . "9000")
                         ("9090" . "9090"))))
                    (oci-container-configuration
                     (image "grafana/grafana:10.0.1")
                     (network "host")
                     (ports
                       '(("3000" . "3000")))
                     (volumes
                       '("/var/lib/grafana:/var/lib/grafana")))))

     In this example two different Shepherd services are going be added to the system.  Each oci-container-configuration record translates to a docker run invocation and its fields directly map to options.  You can refer to the upstream (https://docs.docker.com/engine/reference/commandline/run), documentation for the semantics of each value.  If the images are not found they will be pulled (https://docs.docker.com/engine/reference/commandline/pull/).  The spawned services are going to be attached to the host network and are supposed to behave like other processes.

 -- Data Type: oci-container-configuration
     Available oci-container-configuration fields are:

     user (default: "oci-container") (type: string)
          The user under whose authority docker commands will be run.

     group (default: "docker") (type: string)
          The group under whose authority docker commands will be run.

     command (default: ()) (type: list-of-strings)
          Overwrite the default command (CMD) of the image.

     entrypoint (default: "") (type: string)
          Overwrite the default entrypoint (ENTRYPOINT) of the image.

     environment (default: ()) (type: list)
          Set environment variables. This can be a list of pairs or strings, even mixed:

               (list '("LANGUAGE" . "eo:ca:eu")
                     "JAVA_HOME=/opt/java")

          String are passed directly to the Docker CLI. You can refer to the upstream (https://docs.docker.com/engine/reference/commandline/run/#env) documentation for semantics.

     image (type: string)
          The image used to build the container.  Images are resolved by the Docker Engine, and follow the usual format myregistry.local:5000/testing/test-image:tag.

     provision (default: "") (type: string)
          Set the name of the provisioned Shepherd service.

     network (default: "") (type: string)
          Set a Docker network for the spawned container.

     ports (default: ()) (type: list)
          Set the port or port ranges to expose from the spawned container.  This can be a list of pairs or strings, even mixed:

               (list '("8080" . "80")
                     "10443:443")

          String are passed directly to the Docker CLI.  You can refer to the upstream (https://docs.docker.com/engine/reference/commandline/run/#publish) documentation for semantics.

     volumes (default: ()) (type: list)
          Set volume mappings for the spawned container.  This can be a list of pairs or strings, even mixed:

               (list '("/root/data/grafana" . "/var/lib/grafana")
                     "/gnu/store:/gnu/store")

          String are passed directly to the Docker CLI.  You can refer to the upstream (https://docs.docker.com/engine/reference/commandline/run/#volume) documentation for semantics.

     container-user (default: "") (type: string)
          Set the current user inside the spawned container.  You can refer to the upstream (https://docs.docker.com/engine/reference/run/#user) documentation for semantics.

     workdir (default: "") (type: string)
          Set the current working for the spawned Shepherd service. You can refer to the upstream (https://docs.docker.com/engine/reference/run/#workdir) documentation for semantics.

Auditd Service
..............

The (gnu services auditd) module provides the following service.

 -- Variable: auditd-service-type

     This is the type of the service that runs auditd (https://people.redhat.com/sgrubb/audit/), a daemon that tracks security-relevant information on your system.

     Examples of things that can be tracked:

      1. File accesses

      2. System calls

      3. Invoked commands

      4. Failed login attempts

      5. Firewall filtering

      6. Network access

     auditctl from the audit package can be used in order to add or remove events to be tracked (until the next reboot). In order to permanently track events, put the command line arguments of auditctl into a file called audit.rules in the configuration directory (see below). aureport from the audit package can be used in order to view a report of all recorded events. The audit daemon by default logs into the file /var/log/audit.log.

 -- Data Type: auditd-configuration
     This is the data type representing the configuration of auditd.

     audit (default: audit)
          The audit package to use.

     configuration-directory (default: %default-auditd-configuration-directory)
          The directory containing the configuration file for the audit package, which must be named auditd.conf, and optionally some audit rules to instantiate on startup.

R-Shiny service
...............

The (gnu services science) module provides the following service.

 -- Variable: rshiny-service-type

     This is a type of service which is used to run a webapp created with r-shiny.  This service sets the R_LIBS_USER environment variable and runs the provided script to call runApp.

      -- Data Type: rshiny-configuration
          This is the data type representing the configuration of rshiny.

          package (default: r-shiny)
               The package to use.

          binary (default "rshiny")
               The name of the binary or shell script located at package/bin/ to run when the service is run.

               The common way to create this file is as follows:

                    ...
                    (let* ((out       (assoc-ref %outputs "out"))
                           (targetdir (string-append out "/share/" ,name))
                           (app       (string-append out "/bin/" ,name))
                           (Rbin      (search-input-file %build-inputs "/bin/Rscript")))
                      ;; ...
                      (mkdir-p (string-append out "/bin"))
                      (call-with-output-file app
                        (lambda (port)
                          (format port
                    "#!~a
                    library(shiny)
                    setwd(\"~a\")
                    runApp(launch.browser=0, port=4202)~%\n"
                          Rbin targetdir))))

Nix service
...........

The (gnu services nix) module provides the following service.

 -- Variable: nix-service-type

     This is the type of the service that runs build daemon of the Nix (https://nixos.org/nix/) package manager.  Here is an example showing how to use it:

          (use-modules (gnu))
          (use-service-modules nix)
          (use-package-modules package-management)

          (operating-system
            ;; ...
            (packages (append (list nix)
                              %base-packages))

            (services (append (list (service nix-service-type))
                              %base-services)))

     After guix system reconfigure configure Nix for your user:

       * Add a Nix channel and update it.  See Nix Package Manager Guide (https://nixos.org/nix/manual/).

       * Create a symlink to your profile and activate Nix profile:

          $ ln -s "/nix/var/nix/profiles/per-user/$USER/profile" ~/.nix-profile
          $ source /run/current-system/profile/etc/profile.d/nix.sh

 -- Data Type: nix-configuration
     This data type represents the configuration of the Nix daemon.

     nix (default: nix)
          The Nix package to use.

     sandbox (default: #t)
          Specifies whether builds are sandboxed by default.

     build-directory (default: "/tmp")
          The directory where build directory are stored during builds. This is useful to change if, for example, the default location does not have enough space to hold build trees for big packages.

          This is similar to setting the TMPDIR environment variable for guix-daemon.  TMPDIR, for more info.

     build-sandbox-items (default: '())
          This is a list of strings or objects appended to the build-sandbox-items field of the configuration file.

     extra-config (default: '())
          This is a list of strings or objects appended to the configuration file. It is used to pass extra text to be added verbatim to the configuration file.

     extra-options (default: '())
          Extra command line options for nix-service-type.

Fail2Ban service
................

fail2ban (http://www.fail2ban.org/) scans log files (e.g. /var/log/apache/error_log) and bans IP addresses that show malicious signs -- repeated password failures, attempts to make use of exploits, etc.

fail2ban-service-type service type is provided by the (gnu services security) module.

This service type runs the fail2ban daemon.  It can be configured in various ways, which are:

Basic configuration
     The basic parameters of the Fail2Ban service can be configured via its fail2ban configuration, which is documented below.

User-specified jail extensions
     The fail2ban-jail-service function can be used to add new Fail2Ban jails.

Shepherd extension mechanism
     Service developers can extend the fail2ban-service-type service type itself via the usual service extension mechanism.

 -- Variable: fail2ban-service-type

     This is the type of the service that runs fail2ban daemon.  Below is an example of a basic, explicit configuration:

          (append
           (list
            (service fail2ban-service-type
                     (fail2ban-configuration
                      (extra-jails
                       (list
                        (fail2ban-jail-configuration
                         (name "sshd")
                         (enabled? #t))))))
            ;; There is no implicit dependency on an actual SSH
            ;; service, so you need to provide one.
            (service openssh-service-type))
           %base-services)

 -- Procedure: fail2ban-jail-service svc-type jail
     Extend SVC-TYPE, a <service-type> object with JAIL, a fail2ban-jail-configuration object.

     For example:

          (append
           (list
            (service
             ;; The 'fail2ban-jail-service' procedure can extend any service type
             ;; with a fail2ban jail.  This removes the requirement to explicitly
             ;; extend services with fail2ban-service-type.
             (fail2ban-jail-service
              openssh-service-type
              (fail2ban-jail-configuration
               (name "sshd")
               (enabled? #t)))
             (openssh-configuration ...))))

Below is the reference for the different jail-service-type configuration records.

 -- Data Type: fail2ban-configuration
     Available fail2ban-configuration fields are:

     fail2ban (default: fail2ban) (type: package)
          The fail2ban package to use.  It is used for both binaries and as base default configuration that is to be extended with <fail2ban-jail-configuration> objects.

     run-directory (default: "/var/run/fail2ban") (type: string)
          The state directory for the fail2ban daemon.

     jails (default: '()) (type: list-of-fail2ban-jail-configurations)
          Instances of <fail2ban-jail-configuration> collected from extensions.

     extra-jails (default: '()) (type: list-of-fail2ban-jail-configurations)
          Instances of <fail2ban-jail-configuration> explicitly provided.

     extra-content (default: '()) (type: text-config)
          Extra raw content to add to the end of the jail.local file, provided as a list of file-like objects.

 -- Data Type: fail2ban-ignore-cache-configuration
     Available fail2ban-ignore-cache-configuration fields are:

     key (type: string)
          Cache key.

     max-count (type: integer)
          Cache size.

     max-time (type: integer)
          Cache time.

 -- Data Type: fail2ban-jail-action-configuration
     Available fail2ban-jail-action-configuration fields are:

     name (type: string)
          Action name.

     arguments (default: '()) (type: list-of-arguments)
          Action arguments.

 -- Data Type: fail2ban-jail-configuration
     Available fail2ban-jail-configuration fields are:

     name (type: string)
          Required name of this jail configuration.

     enabled? (default: #t) (type: boolean)
          Whether this jail is enabled.

     backend (type: maybe-symbol)
          Backend to use to detect changes in the log-path.  The default is 'auto.  To consult the defaults of the jail configuration, refer to the /etc/fail2ban/jail.conf file of the fail2ban package.

     max-retry (type: maybe-integer)
          The number of failures before a host gets banned (e.g.  (max-retry 5)).

     max-matches (type: maybe-integer)
          The number of matches stored in ticket (resolvable via tag <matches>) in action.

     find-time (type: maybe-string)
          The time window during which the maximum retry count must be reached for an IP address to be banned.  A host is banned if it has generated max-retry during the last find-time seconds (e.g. (find-time "10m")).  It can be provided in seconds or using Fail2Ban's "time abbreviation format", as described in man 5 jail.conf.

     ban-time (type: maybe-string)
          The duration, in seconds or time abbreviated format, that a ban should last.  (e.g.  (ban-time "10m")).

     ban-time-increment? (type: maybe-boolean)
          Whether to consider past bans to compute increases to the default ban time of a specific IP address.

     ban-time-factor (type: maybe-string)
          The coefficient to use to compute an exponentially growing ban time.

     ban-time-formula (type: maybe-string)
          This is the formula used to calculate the next value of a ban time.

     ban-time-multipliers (type: maybe-string)
          Used to calculate next value of ban time instead of formula.

     ban-time-max-time (type: maybe-string)
          The maximum number of seconds a ban should last.

     ban-time-rnd-time (type: maybe-string)
          The maximum number of seconds a randomized ban time should last.  This can be useful to stop ``clever'' botnets calculating the exact time an IP address can be unbanned again.

     ban-time-overall-jails? (type: maybe-boolean)
          When true, it specifies the search of an IP address in the database should be made across all jails.  Otherwise, only the current jail of the ban IP address is considered.

     ignore-self? (type: maybe-boolean)
          Never ban the local machine's own IP address.

     ignore-ip (default: '()) (type: list-of-strings)
          A list of IP addresses, CIDR masks or DNS hosts to ignore. fail2ban will not ban a host which matches an address in this list.

     ignore-cache (type: maybe-fail2ban-ignore-cache-configuration)
          Provide cache parameters for the ignore failure check.

     filter (type: maybe-fail2ban-jail-filter-configuration)
          The filter to use by the jail, specified via a <fail2ban-jail-filter-configuration> object.  By default, jails have names matching their filter name.

     log-time-zone (type: maybe-string)
          The default time zone for log lines that do not have one.

     log-encoding (type: maybe-symbol)
          The encoding of the log files handled by the jail.  Possible values are: 'ascii, 'utf-8 and 'auto.

     log-path (default: '()) (type: list-of-strings)
          The file names of the log files to be monitored.

     action (default: '()) (type: list-of-fail2ban-jail-actions)
          A list of <fail2ban-jail-action-configuration>.

     extra-content (default: '()) (type: text-config)
          Extra content for the jail configuration, provided as a list of file-like objects.

 -- Data Type: fail2ban-jail-filter-configuration
     Available fail2ban-jail-filter-configuration fields are:

     name (type: string)
          Filter to use.

     mode (type: maybe-string)
          Mode for filter.

Setuid Programs
===============

Some programs need to run with elevated privileges, even when they are launched by unprivileged users.  A notorious example is the passwd program, which users can run to change their password, and which needs to access the /etc/passwd and /etc/shadow files---something normally restricted to root, for obvious security reasons.  To address that, passwd should be setuid-root, meaning that it always runs with root privileges (see How Change Persona (The GNU C Library Reference Manual), for more info about the setuid mechanism).

The store itself cannot contain setuid programs: that would be a security issue since any user on the system can write derivations that populate the store (see The Store).  Thus, a different mechanism is used: instead of changing the setuid or setgid bits directly on files that are in the store, we let the system administrator declare which programs should be entrusted with these additional privileges.

The setuid-programs field of an operating-system declaration contains a list of <setuid-program> denoting the names of programs to have a setuid or setgid bit set (see Using the Configuration System).  For instance, the mount.nfs program, which is part of the nfs-utils package, with a setuid root can be designated like this:

     (setuid-program
       (program (file-append nfs-utils "/sbin/mount.nfs")))

And then, to make mount.nfs setuid on your system, add the previous example to your operating system declaration by appending it to %setuid-programs like this:

     (operating-system
       ;; Some fields omitted...
       (setuid-programs
         (append (list (setuid-program
                         (program (file-append nfs-utils "/sbin/mount.nfs"))))
                 %setuid-programs)))

 -- Data Type: setuid-program
     This data type represents a program with a setuid or setgid bit set.

     program
          A file-like object having its setuid and/or setgid bit set.

     setuid? (default: #t)
          Whether to set user setuid bit.

     setgid? (default: #f)
          Whether to set group setgid bit.

     user (default: 0)
          UID (integer) or user name (string) for the user owner of the program, defaults to root.

     group (default: 0)
          GID (integer) group name (string) for the group owner of the program, defaults to root.

A default set of setuid programs is defined by the %setuid-programs variable of the (gnu system) module.

 -- Variable: %setuid-programs
     A list of <setuid-program> denoting common programs that are setuid-root.

     The list includes commands such as passwd, ping, su, and sudo.

Under the hood, the actual setuid programs are created in the /run/setuid-programs directory at system activation time.  The files in this directory refer to the ``real'' binaries, which are in the store.

X.509 Certificates
==================

Web servers available over HTTPS (that is, HTTP over the transport-layer security mechanism, TLS) send client programs an X.509 certificate that the client can then use to authenticate the server.  To do that, clients verify that the server's certificate is signed by a so-called certificate authority (CA).  But to verify the CA's signature, clients must have first acquired the CA's certificate.

Web browsers such as GNU IceCat include their own set of CA certificates, such that they are able to verify CA signatures out-of-the-box.

However, most other programs that can talk HTTPS---wget, git, w3m, etc.---need to be told where CA certificates can be found.

For users of Guix System, this is done by adding a package that provides certificates to the packages field of the operating-system declaration (see operating-system Reference).  Guix includes one such package, nss-certs, which is a set of CA certificates provided as part of Mozilla's Network Security Services.

Note that it is not part of %base-packages, so you need to explicitly add it.  The /etc/ssl/certs directory, which is where most applications and libraries look for certificates by default, points to the certificates installed globally.

Unprivileged users, including users of Guix on a foreign distro, can also install their own certificate package in their profile.  A number of environment variables need to be defined so that applications and libraries know where to find them.  Namely, the OpenSSL library honors the SSL_CERT_DIR and SSL_CERT_FILE variables.  Some applications add their own environment variables; for instance, the Git version control system honors the certificate bundle pointed to by the GIT_SSL_CAINFO environment variable.  Thus, you would typically run something like:

     guix install nss-certs
     export SSL_CERT_DIR="$HOME/.guix-profile/etc/ssl/certs"
     export SSL_CERT_FILE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
     export GIT_SSL_CAINFO="$SSL_CERT_FILE"

As another example, R requires the CURL_CA_BUNDLE environment variable to point to a certificate bundle, so you would have to run something like this:

     guix install nss-certs
     export CURL_CA_BUNDLE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"

For other applications you may want to look up the required environment variable in the relevant documentation.

Name Service Switch
===================

The (gnu system nss) module provides bindings to the configuration file of the libc name service switch or NSS (see NSS Configuration File (The GNU C Library Reference Manual)).  In a nutshell, the NSS is a mechanism that allows libc to be extended with new ``name'' lookup methods for system databases, which includes host names, service names, user accounts, and more (see System Databases and Name Service Switch (The GNU C Library Reference Manual)).

The NSS configuration specifies, for each system database, which lookup method is to be used, and how the various methods are chained together---for instance, under which circumstances NSS should try the next method in the list.  The NSS configuration is given in the name-service-switch field of operating-system declarations (see name-service-switch).

As an example, the declaration below configures the NSS to use the nss-mdns back-end (https://0pointer.de/lennart/projects/nss-mdns/), which supports host name lookups over multicast DNS (mDNS) for host names ending in .local:

     (name-service-switch
        (hosts (list %files    ;first, check /etc/hosts

                     ;; If the above did not succeed, try
                     ;; with 'mdns_minimal'.
                     (name-service
                       (name "mdns_minimal")

                       ;; 'mdns_minimal' is authoritative for
                       ;; '.local'.  When it returns "not found",
                       ;; no need to try the next methods.
                       (reaction (lookup-specification
                                  (not-found => return))))

                     ;; Then fall back to DNS.
                     (name-service
                       (name "dns"))

                     ;; Finally, try with the "full" 'mdns'.
                     (name-service
                       (name "mdns")))))

Do not worry: the %mdns-host-lookup-nss variable (see below) contains this configuration, so you will not have to type it if all you want is to have .local host lookup working.

Note that, in this case, in addition to setting the name-service-switch of the operating-system declaration, you also need to use avahi-service-type (see avahi-service-type), or %desktop-services, which includes it (see Desktop Services).  Doing this makes nss-mdns accessible to the name service cache daemon (see nscd-service).

For convenience, the following variables provide typical NSS configurations.

 -- Variable: %default-nss
     This is the default name service switch configuration, a name-service-switch object.

 -- Variable: %mdns-host-lookup-nss
     This is the name service switch configuration with support for host name lookup over multicast DNS (mDNS) for host names ending in .local.

The reference for name service switch configuration is given below.  It is a direct mapping of the configuration file format of the C library , so please refer to the C library manual for more information (see NSS Configuration File (The GNU C Library Reference Manual)). Compared to the configuration file format of libc NSS, it has the advantage not only of adding this warm parenthetic feel that we like, but also static checks: you will know about syntax errors and typos as soon as you run guix system.

 -- Data Type: name-service-switch

     This is the data type representation the configuration of libc's name service switch (NSS).  Each field below represents one of the supported system databases.

     aliases
     ethers
     group
     gshadow
     hosts
     initgroups
     netgroup
     networks
     password
     public-key
     rpc
     services
     shadow
          The system databases handled by the NSS.  Each of these fields must be a list of <name-service> objects (see below).

 -- Data Type: name-service

     This is the data type representing an actual name service and the associated lookup action.

     name
          A string denoting the name service (see Services in the NSS configuration (The GNU C Library Reference Manual)).

          Note that name services listed here must be visible to nscd.  This is achieved by passing the #:name-services argument to nscd-service the list of packages providing the needed name services (see nscd-service).

     reaction
          An action specified using the lookup-specification macro (see Actions in the NSS configuration (The GNU C Library Reference Manual)).  For example:

               (lookup-specification (unavailable => continue)
                                     (success => return))

Initial RAM Disk
================

For bootstrapping purposes, the Linux-Libre kernel is passed an initial RAM disk, or initrd.  An initrd contains a temporary root file system as well as an initialization script.  The latter is responsible for mounting the real root file system, and for loading any kernel modules that may be needed to achieve that.

The initrd-modules field of an operating-system declaration allows you to specify Linux-libre kernel modules that must be available in the initrd.  In particular, this is where you would list modules needed to actually drive the hard disk where your root partition is---although the default value of initrd-modules should cover most use cases.  For example, assuming you need the megaraid_sas module in addition to the default modules to be able to access your root file system, you would write:

     (operating-system
       ;; ...
       (initrd-modules (cons "megaraid_sas" %base-initrd-modules)))

 -- Variable: %base-initrd-modules
     This is the list of kernel modules included in the initrd by default.

Furthermore, if you need lower-level customization, the initrd field of an operating-system declaration allows you to specify which initrd you would like to use.  The (gnu system linux-initrd) module provides three ways to build an initrd: the high-level base-initrd procedure and the low-level raw-initrd and expression->initrd procedures.

The base-initrd procedure is intended to cover most common uses. For example, if you want to add a bunch of kernel modules to be loaded at boot time, you can define the initrd field of the operating system declaration like this:

     (initrd (lambda (file-systems . rest)
               ;; Create a standard initrd but set up networking
               ;; with the parameters QEMU expects by default.
               (apply base-initrd file-systems
                      #:qemu-networking? #t
                      rest)))

The base-initrd procedure also handles common use cases that involves using the system as a QEMU guest, or as a ``live'' system with volatile root file system.

The base-initrd procedure is built from raw-initrd procedure. Unlike base-initrd, raw-initrd doesn't do anything high-level, such as trying to guess which kernel modules and packages should be included to the initrd.  An example use of raw-initrd is when a user has a custom Linux kernel configuration and default kernel modules included by base-initrd are not available.

The initial RAM disk produced by base-initrd or raw-initrd honors several options passed on the Linux kernel command line (that is, arguments passed via the linux command of GRUB, or the -append option of QEMU), notably:

gnu.load=BOOT
     Tell the initial RAM disk to load BOOT, a file containing a Scheme program, once it has mounted the root file system.

     Guix uses this option to yield control to a boot program that runs the service activation programs and then spawns the GNU Shepherd, the initialization system.

root=ROOT
     Mount ROOT as the root file system.  ROOT can be a device name like /dev/sda1, a file system label, or a file system UUID. When unspecified, the device name from the root file system of the operating system declaration is used.

rootfstype=TYPE
     Set the type of the root file system.  It overrides the type field of the root file system specified via the operating-system declaration, if any.

rootflags=OPTIONS
     Set the mount options of the root file system.  It overrides the options field of the root file system specified via the operating-system declaration, if any.

fsck.mode=MODE
     Whether to check the ROOT file system for errors before mounting it.  MODE is one of skip (never check), force (always check), or auto to respect the root <file-system> object's check? setting (see File Systems) and run a full scan only if the file system was not cleanly shut down.

     auto is the default if this option is not present or if MODE is not one of the above.

fsck.repair=LEVEL
     The level of repairs to perform automatically if errors are found in the ROOT file system.  LEVEL is one of no (do not write to ROOT at all if possible), yes (repair as much as possible), or preen to repair problems considered safe to repair automatically.

     preen is the default if this option is not present or if LEVEL is not one of the above.

gnu.system=SYSTEM
     Have /run/booted-system and /run/current-system point to SYSTEM.

modprobe.blacklist=MODULES...
     Instruct the initial RAM disk as well as the modprobe command (from the kmod package) to refuse to load MODULES.  MODULES must be a comma-separated list of module names---e.g., usbkbd,9pnet.

gnu.repl
     Start a read-eval-print loop (REPL) from the initial RAM disk before it tries to load kernel modules and to mount the root file system.  Our marketing team calls it boot-to-Guile.  The Schemer in you will love it.  See Using Guile Interactively (GNU Guile Reference Manual), for more information on Guile's REPL.

Now that you know all the features that initial RAM disks produced by base-initrd and raw-initrd provide, here is how to use it and customize it further.

 -- Procedure: raw-initrd file-systems
     [#:linux-modules '()] [#:pre-mount #t] [#:mapped-devices '()]
     [#:keyboard-layout #f] [#:helper-packages '()]
     [#:qemu-networking? #f] [#:volatile-root? #f]
     Return a derivation that builds a raw initrd.  FILE-SYSTEMS is a list of file systems to be mounted by the initrd, possibly in addition to the root file system specified on the kernel command line via root. LINUX-MODULES is a list of kernel modules to be loaded at boot time. MAPPED-DEVICES is a list of device mappings to realize before FILE-SYSTEMS are mounted (see Mapped Devices). PRE-MOUNT is a G-expression to evaluate before realizing MAPPED-DEVICES. HELPER-PACKAGES is a list of packages to be copied in the initrd. It may include e2fsck/static or other packages needed by the initrd to check the root file system.

     When true, KEYBOARD-LAYOUT is a <keyboard-layout> record denoting the desired console keyboard layout.  This is done before MAPPED-DEVICES are set up and before FILE-SYSTEMS are mounted such that, should the user need to enter a passphrase or use the REPL, this happens using the intended keyboard layout.

     When QEMU-NETWORKING? is true, set up networking with the standard QEMU parameters.  When VIRTIO? is true, load additional modules so that the initrd can be used as a QEMU guest with para-virtualized I/O drivers.

     When VOLATILE-ROOT? is true, the root file system is writable but any changes to it are lost.

 -- Procedure: base-initrd file-systems
     [#:mapped-devices '()] [#:keyboard-layout #f]
     [#:qemu-networking? #f] [#:volatile-root? #f]
     [#:linux-modules '()]
     Return as a file-like object a generic initrd, with kernel modules taken from LINUX.  FILE-SYSTEMS is a list of file-systems to be mounted by the initrd, possibly in addition to the root file system specified on the kernel command line via root.  MAPPED-DEVICES is a list of device mappings to realize before FILE-SYSTEMS are mounted.

     When true, KEYBOARD-LAYOUT is a <keyboard-layout> record denoting the desired console keyboard layout.  This is done before MAPPED-DEVICES are set up and before FILE-SYSTEMS are mounted such that, should the user need to enter a passphrase or use the REPL, this happens using the intended keyboard layout.

     QEMU-NETWORKING? and VOLATILE-ROOT? behaves as in raw-initrd.

     The initrd is automatically populated with all the kernel modules necessary for FILE-SYSTEMS and for the given options.  Additional kernel modules can be listed in LINUX-MODULES.  They will be added to the initrd, and loaded at boot time in the order in which they appear.

Needless to say, the initrds we produce and use embed a statically-linked Guile, and the initialization program is a Guile program.  That gives a lot of flexibility.  The expression->initrd procedure builds such an initrd, given the program to run in that initrd.

 -- Procedure: expression->initrd exp
     [#:guile %guile-static-stripped] [#:name "guile-initrd"]
     Return as a file-like object a Linux initrd (a gzipped cpio archive) containing GUILE and that evaluates EXP, a G-expression, upon booting.  All the derivations referenced by EXP are automatically copied to the initrd.

Bootloader Configuration
========================

The operating system supports multiple bootloaders.  The bootloader is configured using bootloader-configuration declaration.  All the fields of this structure are bootloader agnostic except for one field, bootloader that indicates the bootloader to be configured and installed.

Some of the bootloaders do not honor every field of bootloader-configuration.  For instance, the extlinux bootloader does not support themes and thus ignores the theme field.

 -- Data Type: bootloader-configuration
     The type of a bootloader configuration declaration.

     bootloader
          The bootloader to use, as a bootloader object.  For now grub-bootloader, grub-efi-bootloader, grub-efi-removable-bootloader, grub-efi-netboot-bootloader, grub-efi-netboot-removable-bootloader, extlinux-bootloader and u-boot-bootloader are supported.

          Available bootloaders are described in (gnu bootloader ...) modules.  In particular, (gnu bootloader u-boot) contains definitions of bootloaders for a wide range of ARM and AArch64 systems, using the U-Boot bootloader (https://www.denx.de/wiki/U-Boot/).

          grub-bootloader allows you to boot in particular Intel-based machines in ``legacy'' BIOS mode.

          grub-efi-bootloader allows to boot on modern systems using the Unified Extensible Firmware Interface (UEFI).  This is what you should use if the installation image contains a /sys/firmware/efi directory when you boot it on your system.

          grub-efi-removable-bootloader allows you to boot your system from removable media by writing the GRUB file to the UEFI-specification location of /EFI/BOOT/BOOTX64.efi of the boot directory, usually /boot/efi. This is also useful for some UEFI firmwares that ``forget'' their configuration from their non-volatile storage. Like grub-efi-bootloader, this can only be used if the /sys/firmware/efi directory is available.

               This will overwrite the GRUB file from any other operating systems that also place their GRUB file in the UEFI-specification location; making them unbootable.

          grub-efi-netboot-bootloader allows you to boot your system over network through TFTP.  In combination with an NFS root file system this allows you to build a diskless Guix system.

          The installation of the grub-efi-netboot-bootloader generates the content of the TFTP root directory at targets (see targets) below the sub-directory efi/Guix, to be served by a TFTP server.  You may want to mount your TFTP server directories onto the targets to move the required files to the TFTP server automatically during installation.

          If you plan to use an NFS root file system as well (actually if you mount the store from an NFS share), then the TFTP server needs to serve the file /boot/grub/grub.cfg and other files from the store (like GRUBs background image, the kernel (see kernel) and the initrd (see initrd)), too.  All these files from the store will be accessed by GRUB through TFTP with their normal store path, for example as tftp://tftp-server/gnu/store/…-initrd/initrd.cpio.gz.

          Two symlinks are created to make this possible.  For each target in the targets field, the first symlink is target/efi/Guix/boot/grub/grub.cfg pointing to ../../../boot/grub/grub.cfg, where target may be /boot.  In this case the link is not leaving the served TFTP root directory, but otherwise it does.  The second link is target/gnu/store and points to ../gnu/store.  This link is leaving the served TFTP root directory.

          The assumption behind all this is that you have an NFS server exporting the root file system for your Guix system, and additionally a TFTP server exporting your targets directories—usually a single /boot—from that same root file system for your Guix system.  In this constellation the symlinks will work.

          For other constellations you will have to program your own bootloader installer, which then takes care to make necessary files from the store accessible through TFTP, for example by copying them into the TFTP root directory for your targets.

          It is important to note that symlinks pointing outside the TFTP root directory may need to be allowed in the configuration of your TFTP server.  Further the store link exposes the whole store through TFTP.  Both points need to be considered carefully for security aspects.  It is advised to disable any TFTP write access!

          Please note, that this bootloader will not modify the ‘UEFI Boot Manager’ of the system.

          Beside the grub-efi-netboot-bootloader, the already mentioned TFTP and NFS servers, you also need a properly configured DHCP server to make the booting over netboot possible.  For all this we can currently only recommend you to look for instructions about PXE (Preboot eXecution Environment).

          If a local EFI System Partition (ESP) or a similar partition with a FAT file system is mounted in targets, then symlinks cannot be created.  In this case everything will be prepared for booting from local storage, matching the behavior of grub-efi-bootloader, with the difference that all GRUB binaries are copied to targets, necessary for booting over the network.

          grub-efi-netboot-removable-bootloader is identical to grub-efi-netboot-bootloader with the exception that the sub-directory efi/boot will be used instead of efi/Guix to comply with the UEFI specification for removable media.

               This will overwrite the GRUB file from any other operating systems that also place their GRUB file in the UEFI-specification location; making them unbootable.

     targets
          This is a list of strings denoting the targets onto which to install the bootloader.

          The interpretation of targets depends on the bootloader in question. For grub-bootloader, for example, they should be device names understood by the bootloader installer command, such as /dev/sda or (hd0) (see Invoking grub-install (GNU GRUB Manual)).  For grub-efi-bootloader and grub-efi-removable-bootloader they should be mount points of the EFI file system, usually /boot/efi.  For grub-efi-netboot-bootloader, targets should be the mount points corresponding to TFTP root directories served by your TFTP server.

     menu-entries (default: '())
          A possibly empty list of menu-entry objects (see below), denoting entries to appear in the bootloader menu, in addition to the current system entry and the entry pointing to previous system generations.

     default-entry (default: 0)
          The index of the default boot menu entry.  Index 0 is for the entry of the current system.

     timeout (default: 5)
          The number of seconds to wait for keyboard input before booting.  Set to 0 to boot immediately, and to -1 to wait indefinitely.

     keyboard-layout (default: #f)
          If this is #f, the bootloader's menu (if any) uses the default keyboard layout, usually US English (``qwerty'').

          Otherwise, this must be a keyboard-layout object (see Keyboard Layout).

               This option is currently ignored by bootloaders other than grub and grub-efi.

     theme (default: #F)
          The bootloader theme object describing the theme to use.  If no theme is provided, some bootloaders might use a default theme, that's true for GRUB.

     terminal-outputs (default: '(gfxterm))
          The output terminals used for the bootloader boot menu, as a list of symbols.  GRUB accepts the values: console, serial, serial_{0-3}, gfxterm, vga_text, mda_text, morse, and pkmodem.  This field corresponds to the GRUB variable GRUB_TERMINAL_OUTPUT (see Simple configuration (GNU GRUB manual)).

     terminal-inputs (default: '())
          The input terminals used for the bootloader boot menu, as a list of symbols.  For GRUB, the default is the native platform terminal as determined at run-time.  GRUB accepts the values: console, serial, serial_{0-3}, at_keyboard, and usb_keyboard.  This field corresponds to the GRUB variable GRUB_TERMINAL_INPUT (see Simple configuration (GNU GRUB manual)).

     serial-unit (default: #f)
          The serial unit used by the bootloader, as an integer from 0 to 3. For GRUB, it is chosen at run-time; currently GRUB chooses 0, which corresponds to COM1 (see Serial terminal (GNU GRUB manual)).

     serial-speed (default: #f)
          The speed of the serial interface, as an integer.  For GRUB, the default value is chosen at run-time; currently GRUB chooses 9600 bps (see Serial terminal (GNU GRUB manual)).

     device-tree-support? (default: #t)
          Whether to support Linux device tree (https://en.wikipedia.org/wiki/Devicetree) files loading.

          This option in enabled by default.  In some cases involving the u-boot bootloader, where the device tree has already been loaded in RAM, it can be handy to disable the option by setting it to #f.

     extra-initrd (default: #f)
          File name of an additional initrd to load during the boot.  It may or may not point to a file in the store, but the main use case is for out-of-store files containing secrets.

          In order to be able to provide decryption keys for the LUKS device, they need to be available in the initial ram disk.  However they cannot be stored inside the usual initrd, since it is stored in the store and being a world-readable (as files in the store are) is not a desired property for a initrd containing decryption keys.  You can therefore use this field to instruct GRUB to also load a manually created initrd not stored in the store.

          For any use case not involving secrets, you should use regular initrd (see initrd) instead.

          Suitable image can be created for example like this:

               echo /key-file.bin | cpio -oH newc >/key-file.cpio
               chmod 0000 /key-file.cpio

          After it is created, you can use it in this manner:

               ;; Operating system with encrypted boot partition
               (operating-system
                 ...
                 (bootloader (bootloader-configuration
                              (bootloader grub-efi-bootloader)
                              (targets '("/boot/efi"))
                              ;; Load the initrd with a key file
                              (extra-initrd "/key-file.cpio")))
                 (mapped-devices
                  (list (mapped-device
                         (source (uuid "12345678-1234-1234-1234-123456789abc"))
                         (target "my-root")
                         (type (luks-device-mapping-with-options
                                ;; And use it to unlock the root device
                                #:key-file "/key-file.bin"))))))

          Be careful when using this option, since pointing to a file that is not readable by the grub while booting will cause the boot to fail and require a manual edit of the initrd line in the grub menu.

          Currently only supported by GRUB.

Should you want to list additional boot menu entries via the menu-entries field above, you will need to create them with the menu-entry form.  For example, imagine you want to be able to boot another distro (hard to imagine!), you can define a menu entry along these lines:

     (menu-entry
       (label "The Other Distro")
       (linux "/boot/old/vmlinux-2.6.32")
       (linux-arguments '("root=/dev/sda2"))
       (initrd "/boot/old/initrd"))

Details below.

 -- Data Type: menu-entry
     The type of an entry in the bootloader menu.

     label
          The label to show in the menu---e.g., "GNU".

     linux (default: #f)
          The Linux kernel image to boot, for example:

               (file-append linux-libre "/bzImage")

          For GRUB, it is also possible to specify a device explicitly in the file path using GRUB's device naming convention (see Naming convention (GNU GRUB manual)), for example:

               "(hd0,msdos1)/boot/vmlinuz"

          If the device is specified explicitly as above, then the device field is ignored entirely.

     linux-arguments (default: '())
          The list of extra Linux kernel command-line arguments---e.g., '("console=ttyS0").

     initrd (default: #f)
          A G-Expression or string denoting the file name of the initial RAM disk to use (see G-Expressions).

     device (default: #f)
          The device where the kernel and initrd are to be found---i.e., for GRUB, root for this menu entry (see root (GNU GRUB manual)).

          This may be a file system label (a string), a file system UUID (a bytevector, see File Systems), or #f, in which case the bootloader will search the device containing the file specified by the linux field (see search (GNU GRUB manual)).  It must not be an OS device name such as /dev/sda1.

     multiboot-kernel (default: #f)
          The kernel to boot in Multiboot-mode (see multiboot (GNU GRUB manual)).  When this field is set, a Multiboot menu-entry is generated. For example:

               (file-append mach "/boot/gnumach")

     multiboot-arguments (default: '())
          The list of extra command-line arguments for the multiboot-kernel.

          For example, when running in QEMU it can be useful to use a text-based console (use options --nographic --serial mon:stdio):

               '("console=com0")

          To use the new and still experimental rumpdisk user-level disk driver (https://darnassus.sceen.net/~hurd-web/rump_kernel/) instead of GNU Mach's in-kernel IDE driver, set kernel-arguments to:

               '("noide")

          Of course, these options can be combined:

               '("console=com0" "noide")

     multiboot-modules (default: '())
          The list of commands for loading Multiboot modules.  For example:

               (list (list (file-append hurd "/hurd/ext2fs.static") "ext2fs"
                            ...)
                     (list (file-append libc "/lib/ld.so.1") "exec"
                            ...))

     chain-loader (default: #f)
          A string that can be accepted by grub's chainloader directive. This has no effect if either linux or multiboot-kernel fields are specified. The following is an example of chainloading a different GNU/Linux system.

               (bootloader
                (bootloader-configuration
                 ;; ...
                 (menu-entries
                  (list
                   (menu-entry
                    (label "GNU/Linux")
                    (device (uuid "1C31-A17C" 'fat))
                    (chain-loader "/EFI/GNULinux/grubx64.efi"))))))

For now only GRUB has theme support.  GRUB themes are created using the grub-theme form, which is not fully documented yet.

 -- Data Type: grub-theme
     Data type representing the configuration of the GRUB theme.

     gfxmode (default: '("auto"))
          The GRUB gfxmode to set (a list of screen resolution strings, see gfxmode (GNU GRUB manual)).

 -- Procedure: grub-theme
     Return the default GRUB theme used by the operating system if no theme field is specified in bootloader-configuration record.

     It comes with a fancy background image displaying the GNU and Guix logos.

For example, to override the default resolution, you may use something like

     (bootloader
      (bootloader-configuration
      ;; ...
      (theme (grub-theme
              (inherit (grub-theme))
              (gfxmode '("1024x786x32" "auto"))))))

Invoking guix system
====================

Once you have written an operating system declaration as seen in the previous section, it can be instantiated using the guix system command.  The synopsis is:

     guix system OPTIONS... ACTION FILE

FILE must be the name of a file containing an operating-system declaration.  ACTION specifies how the operating system is instantiated.  Currently the following values are supported:

search
     Display available service type definitions that match the given regular expressions, sorted by relevance:

          $ guix system search console
          name: console-fonts
          location: gnu/services/base.scm:806:2
          extends: shepherd-root
          description: Install the given fonts on the specified ttys (fonts are per
          + virtual console on GNU/Linux).  The value of this service is a list of
          + tty/font pairs.  The font can be the name of a font provided by the `kbd'
          + package or any valid argument to `setfont', as in this example:
          +
          +      '(("tty1" . "LatGrkCyr-8x16")
          +        ("tty2" . (file-append
          +                      font-tamzen
          +                      "/share/kbd/consolefonts/TamzenForPowerline10x20.psf"))
          +        ("tty3" . (file-append
          +                      font-terminus
          +                      "/share/consolefonts/ter-132n"))) ; for HDPI
          relevance: 9

          name: mingetty
          location: gnu/services/base.scm:1190:2
          extends: shepherd-root
          description: Provide console login using the `mingetty' program.
          relevance: 2

          name: login
          location: gnu/services/base.scm:860:2
          extends: pam
          description: Provide a console log-in service as specified by its
          + configuration value, a `login-configuration' object.
          relevance: 2

          ...

     As for guix package --search, the result is written in recutils format, which makes it easy to filter the output (see GNU recutils databases (GNU recutils manual)).

edit
     Edit or view the definition of the given service types.

     For example, the command below opens your editor, as specified by the EDITOR environment variable, on the definition of the openssh service type:

          guix system edit openssh

reconfigure
     Build the operating system described in FILE, activate it, and switch to it (This action (and the related actions switch-generation and roll-back) are usable only on systems already running Guix System.).

          It is highly recommended to run guix pull once before you run guix system reconfigure for the first time (see Invoking guix pull).  Failing to do that you would see an older version of Guix once reconfigure has completed.

     This effects all the configuration specified in FILE: user accounts, system services, global package list, setuid programs, etc. The command starts system services specified in FILE that are not currently running; if a service is currently running this command will arrange for it to be upgraded the next time it is stopped (e.g. by herd stop X or herd restart X).

     This command creates a new generation whose number is one greater than the current generation (as reported by guix system list-generations).  If that generation already exists, it will be overwritten.  This behavior mirrors that of guix package (see Invoking guix package).

     It also adds a bootloader menu entry for the new OS configuration, ---unless --no-bootloader is passed.  For GRUB, it moves entries for older configurations to a submenu, allowing you to choose an older system generation at boot time should you need it.

     Upon completion, the new system is deployed under /run/current-system.  This directory contains provenance meta-data: the list of channels in use (see Channels) and FILE itself, when available.  You can view it by running:

          guix system describe

     This information is useful should you later want to inspect how this particular generation was built.  In fact, assuming FILE is self-contained, you can later rebuild generation N of your operating system with:

          guix time-machine \
            -C /var/guix/profiles/system-N-link/channels.scm -- \
            system reconfigure \
            /var/guix/profiles/system-N-link/configuration.scm

     You can think of it as some sort of built-in version control!  Your system is not just a binary artifact: it carries its own source. See provenance-service-type, for more information on provenance tracking.

     By default, reconfigure prevents you from downgrading your system, which could (re)introduce security vulnerabilities and also cause problems with ``stateful'' services such as database management systems.  You can override that behavior by passing --allow-downgrades.

switch-generation
     Switch to an existing system generation.  This action atomically switches the system profile to the specified system generation.  It also rearranges the system's existing bootloader menu entries.  It makes the menu entry for the specified system generation the default, and it moves the entries for the other generations to a submenu, if supported by the bootloader being used.  The next time the system boots, it will use the specified system generation.

     The bootloader itself is not being reinstalled when using this command.  Thus, the installed bootloader is used with an updated configuration file.

     The target generation can be specified explicitly by its generation number.  For example, the following invocation would switch to system generation 7:

          guix system switch-generation 7

     The target generation can also be specified relative to the current generation with the form +N or -N, where +3 means ``3 generations ahead of the current generation,'' and -1 means ``1 generation prior to the current generation.''  When specifying a negative value such as -1, you must precede it with -- to prevent it from being parsed as an option.  For example:

          guix system switch-generation -- -1

     Currently, the effect of invoking this action is only to switch the system profile to an existing generation and rearrange the bootloader menu entries.  To actually start using the target system generation, you must reboot after running this action.  In the future, it will be updated to do the same things as reconfigure, like activating and deactivating services.

     This action will fail if the specified generation does not exist.

roll-back
     Switch to the preceding system generation.  The next time the system boots, it will use the preceding system generation.  This is the inverse of reconfigure, and it is exactly the same as invoking switch-generation with an argument of -1.

     Currently, as with switch-generation, you must reboot after running this action to actually start using the preceding system generation.

delete-generations
     Delete system generations, making them candidates for garbage collection (see Invoking guix gc, for information on how to run the ``garbage collector'').

     This works in the same way as guix package --delete-generations (see --delete-generations).  With no arguments, all system generations but the current one are deleted:

          guix system delete-generations

     You can also select the generations you want to delete.  The example below deletes all the system generations that are more than two months old:

          guix system delete-generations 2m

     Running this command automatically reinstalls the bootloader with an updated list of menu entries---e.g., the ``old generations'' sub-menu in GRUB no longer lists the generations that have been deleted.

build
     Build the derivation of the operating system, which includes all the configuration files and programs needed to boot and run the system. This action does not actually install anything.

init
     Populate the given directory with all the files necessary to run the operating system specified in FILE.  This is useful for first-time installations of Guix System.  For instance:

          guix system init my-os-config.scm /mnt

     copies to /mnt all the store items required by the configuration specified in my-os-config.scm.  This includes configuration files, packages, and so on.  It also creates other essential files needed for the system to operate correctly---e.g., the /etc, /var, and /run directories, and the /bin/sh file.

     This command also installs bootloader on the targets specified in my-os-config, unless the --no-bootloader option was passed.

vm
     Build a virtual machine (VM) that contains the operating system declared in FILE, and return a script to run that VM.

          The vm action and others below can use KVM support in the Linux-libre kernel.  Specifically, if the machine has hardware virtualization support, the corresponding KVM kernel module should be loaded, and the /dev/kvm device node must exist and be readable and writable by the user and by the build users of the daemon (see Build Environment Setup).

     Arguments given to the script are passed to QEMU as in the example below, which enables networking and requests 1 GiB of RAM for the emulated machine:

          $ /gnu/store/...-run-vm.sh -m 1024 -smp 2 -nic user,model=virtio-net-pci

     It's possible to combine the two steps into one:

          $ $(guix system vm my-config.scm) -m 1024 -smp 2 -nic user,model=virtio-net-pci

     The VM shares its store with the host system.

     By default, the root file system of the VM is mounted volatile; the --persistent option can be provided to make it persistent instead.  In that case, the VM disk-image file will be copied from the store to the TMPDIR directory to make it writable.

     Additional file systems can be shared between the host and the VM using the --share and --expose command-line options: the former specifies a directory to be shared with write access, while the latter provides read-only access to the shared directory.

     The example below creates a VM in which the user's home directory is accessible read-only, and where the /exchange directory is a read-write mapping of $HOME/tmp on the host:

          guix system vm my-config.scm \
             --expose=$HOME --share=$HOME/tmp=/exchange

     On GNU/Linux, the default is to boot directly to the kernel; this has the advantage of requiring only a very tiny root disk image since the store of the host can then be mounted.

     The --full-boot option forces a complete boot sequence, starting with the bootloader.  This requires more disk space since a root image containing at least the kernel, initrd, and bootloader data files must be created.

     The --image-size option can be used to specify the size of the image.

     The --no-graphic option will instruct guix system to spawn a headless VM that will use the invoking tty for IO.  Among other things, this enables copy-pasting, and scrollback.  Use the ctrl-a prefix to issue QEMU commands; e.g. ctrl-a h prints a help, ctrl-a x quits the VM, and ctrl-a c switches between the QEMU monitor and the VM.

image
     The image command can produce various image types.  The image type can be selected using the --image-type option.  It defaults to mbr-hybrid-raw.  When its value is iso9660, the --label option can be used to specify a volume ID with image.  By default, the root file system of a disk image is mounted non-volatile; the --volatile option can be provided to make it volatile instead.  When using image, the bootloader installed on the generated image is taken from the provided operating-system definition.  The following example demonstrates how to generate an image that uses the grub-efi-bootloader bootloader and boot it with QEMU:

          image=$(guix system image --image-type=qcow2 \
                  gnu/system/examples/lightweight-desktop.tmpl)
          cp $image /tmp/my-image.qcow2
          chmod +w /tmp/my-image.qcow2
          qemu-system-x86_64 -enable-kvm -hda /tmp/my-image.qcow2 -m 1000 \
                             -bios $(guix build ovmf)/share/firmware/ovmf_x64.bin

     When using the mbr-hybrid-raw image type, a raw disk image is produced; it can be copied as is to a USB stick, for instance.  Assuming /dev/sdc is the device corresponding to a USB stick, one can copy the image to it using the following command:

          # dd if=$(guix system image my-os.scm) of=/dev/sdc status=progress

     The --list-image-types command lists all the available image types.

     When using the qcow2 image type, the returned image is in qcow2 format, which the QEMU emulator can efficiently use. See Running Guix in a VM, for more information on how to run the image in a virtual machine.  The grub-bootloader bootloader is always used independently of what is declared in the operating-system file passed as argument.  This is to make it easier to work with QEMU, which uses the SeaBIOS BIOS by default, expecting a bootloader to be installed in the Master Boot Record (MBR).

     When using the docker image type, a Docker image is produced. Guix builds the image from scratch, not from a pre-existing Docker base image.  As a result, it contains exactly what you define in the operating system configuration file.  You can then load the image and launch a Docker container using commands like the following:

          image_id="$(docker load < guix-system-docker-image.tar.gz)"
          container_id="$(docker create $image_id)"
          docker start $container_id

     This command starts a new Docker container from the specified image.  It will boot the Guix system in the usual manner, which means it will start any services you have defined in the operating system configuration.  You can get an interactive shell running in the container using docker exec:

          docker exec -ti $container_id /run/current-system/profile/bin/bash --login

     Depending on what you run in the Docker container, it may be necessary to give the container additional permissions.  For example, if you intend to build software using Guix inside of the Docker container, you may need to pass the --privileged option to docker create.

     Last, the --network option applies to guix system docker-image: it produces an image where network is supposedly shared with the host, and thus without services like nscd or NetworkManager.

container
     Return a script to run the operating system declared in FILE within a container.  Containers are a set of lightweight isolation mechanisms provided by the kernel Linux-libre.  Containers are substantially less resource-demanding than full virtual machines since the kernel, shared objects, and other resources can be shared with the host system; this also means they provide thinner isolation.

     Currently, the script must be run as root in order to support more than a single user and group.  The container shares its store with the host system.

     As with the vm action (see guix system vm), additional file systems to be shared between the host and container can be specified using the --share and --expose options:

          guix system container my-config.scm \
             --expose=$HOME --share=$HOME/tmp=/exchange

     The --share and --expose options can also be passed to the generated script to bind-mount additional directories into the container.

          This option requires Linux-libre 3.19 or newer.

OPTIONS can contain any of the common build options (see Common Build Options).  In addition, OPTIONS can contain one of the following:

--expression=EXPR
-e EXPR
     Consider the operating-system EXPR evaluates to. This is an alternative to specifying a file which evaluates to an operating system. This is used to generate the Guix system installer see Building the Installation Image).

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM instead of the host system type. This works as per guix build (see Invoking guix build).

--target=TRIPLET
     Cross-build for TRIPLET, which must be a valid GNU triplet, such as "aarch64-linux-gnu" (see GNU configuration triplets (Autoconf)).

--derivation
-d
     Return the derivation file name of the given operating system without building anything.

--save-provenance
     As discussed above, guix system init and guix system reconfigure always save provenance information via a dedicated service (see provenance-service-type). However, other commands don't do that by default.  If you wish to, say, create a virtual machine image that contains provenance information, you can run:

          guix system image -t qcow2 --save-provenance config.scm

     That way, the resulting image will effectively ``embed its own source'' in the form of meta-data in /run/current-system.  With that information, one can rebuild the image to make sure it really contains what it pretends to contain; or they could use that to derive a variant of the image.

--image-type=TYPE
-t TYPE
     For the image action, create an image with given TYPE.

     When this option is omitted, guix system uses the mbr-hybrid-raw image type.

     --image-type=iso9660 produces an ISO-9660 image, suitable for burning on CDs and DVDs.

--image-size=SIZE
     For the image action, create an image of the given SIZE. SIZE may be a number of bytes, or it may include a unit as a suffix (see size specifications (GNU Coreutils)).

     When this option is omitted, guix system computes an estimate of the image size as a function of the size of the system declared in FILE.

--network
-N
     For the container action, allow containers to access the host network, that is, do not create a network namespace.

--root=FILE
-r FILE
     Make FILE a symlink to the result, and register it as a garbage collector root.

--skip-checks
     Skip pre-installation safety checks.

     By default, guix system init and guix system reconfigure perform safety checks: they make sure the file systems that appear in the operating-system declaration actually exist (see File Systems), and that any Linux kernel modules that may be needed at boot time are listed in initrd-modules (see Initial RAM Disk).  Passing this option skips these tests altogether.

--allow-downgrades
     Instruct guix system reconfigure to allow system downgrades.

     By default, reconfigure prevents you from downgrading your system.  It achieves that by comparing the provenance info of your system (shown by guix system describe) with that of your guix command (shown by guix describe).  If the commits for guix are not descendants of those used for your system, guix system reconfigure errors out.  Passing --allow-downgrades allows you to bypass these checks.

          Make sure you understand its security implications before using --allow-downgrades.

--on-error=STRATEGY
     Apply STRATEGY when an error occurs when reading FILE. STRATEGY may be one of the following:

     nothing-special
          Report the error concisely and exit.  This is the default strategy.

     backtrace
          Likewise, but also display a backtrace.

     debug
          Report the error and enter Guile's debugger.  From there, you can run commands such as ,bt to get a backtrace, ,locals to display local variable values, and more generally inspect the state of the program.  See Debug Commands (GNU Guile Reference Manual), for a list of available debugging commands.

Once you have built, configured, re-configured, and re-re-configured your Guix installation, you may find it useful to list the operating system generations available on disk---and that you can choose from the bootloader boot menu:

describe
     Describe the running system generation: its file name, the kernel and bootloader used, etc., as well as provenance information when available.

     The --list-installed flag is available, with the same syntax that is used in guix package --list-installed (see Invoking guix package).  When the flag is used, the description will include a list of packages that are currently installed in the system profile, with optional filtering based on a regular expression.

          The running system generation---referred to by /run/current-system---is not necessarily the current system generation---referred to by /var/guix/profiles/system: it differs when, for instance, you chose from the bootloader menu to boot an older generation.

          It can also differ from the booted system generation---referred to by /run/booted-system---for instance because you reconfigured the system in the meantime.

list-generations
     List a summary of each generation of the operating system available on disk, in a human-readable way.  This is similar to the --list-generations option of guix package (see Invoking guix package).

     Optionally, one can specify a pattern, with the same syntax that is used in guix package --list-generations, to restrict the list of generations displayed.  For instance, the following command displays generations that are up to 10 days old:

          $ guix system list-generations 10d

     The --list-installed flag may also be specified, with the same syntax that is used in guix package --list-installed.  This may be helpful if trying to determine when a package was added to the system.

The guix system command has even more to offer!  The following sub-commands allow you to visualize how your system services relate to each other:

extension-graph
     Emit to standard output the service extension graph of the operating system defined in FILE (see Service Composition, for more information on service extensions).  By default the output is in Dot/Graphviz format, but you can choose a different format with --graph-backend, as with guix graph (see --backend):

     The command:

          $ guix system extension-graph FILE | xdot -

     shows the extension relations among services.

          The dot program is provided by the graphviz package.

shepherd-graph
     Emit to standard output the dependency graph of shepherd services of the operating system defined in FILE.  See Shepherd Services, for more information and for an example graph.

     Again, the default output format is Dot/Graphviz, but you can pass --graph-backend to select a different one.

Invoking guix deploy
====================

We've already seen operating-system declarations used to manage a machine's configuration locally.  Suppose you need to configure multiple machines, though---perhaps you're managing a service on the web that's comprised of several servers.  guix deploy enables you to use those same operating-system declarations to manage multiple remote hosts at once as a logical ``deployment''.

     The functionality described in this section is still under development and is subject to change.  Get in touch with us on guix-devel@gnu.org!

     guix deploy FILE

Such an invocation will deploy the machines that the code within FILE evaluates to.  As an example, FILE might contain a definition like this:

     ;; This is a Guix deployment of a "bare bones" setup, with
     ;; no X11 display server, to a machine with an SSH daemon
     ;; listening on localhost:2222. A configuration such as this
     ;; may be appropriate for virtual machine with ports
     ;; forwarded to the host's loopback interface.

     (use-service-modules networking ssh)
     (use-package-modules bootloaders)

     (define %system
       (operating-system
        (host-name "gnu-deployed")
        (timezone "Etc/UTC")
        (bootloader (bootloader-configuration
                     (bootloader grub-bootloader)
                     (targets '("/dev/vda"))
                     (terminal-outputs '(console))))
        (file-systems (cons (file-system
                             (mount-point "/")
                             (device "/dev/vda1")
                             (type "ext4"))
                            %base-file-systems))
        (services
         (append (list (service dhcp-client-service-type)
                       (service openssh-service-type
                                (openssh-configuration
                                 (permit-root-login #t)
                                 (allow-empty-passwords? #t))))
                 %base-services))))

     (list (machine
            (operating-system %system)
            (environment managed-host-environment-type)
            (configuration (machine-ssh-configuration
                            (host-name "localhost")
                            (system "x86_64-linux")
                            (user "alice")
                            (identity "./id_rsa")
                            (port 2222)))))

The file should evaluate to a list of MACHINE objects.  This example, upon being deployed, will create a new generation on the remote system realizing the operating-system declaration %system. environment and configuration specify how the machine should be provisioned---that is, how the computing resources should be created and managed.  The above example does not create any resources, as a 'managed-host is a machine that is already running the Guix system and available over the network.  This is a particularly simple case; a more complex deployment may involve, for example, starting virtual machines through a Virtual Private Server (VPS) provider.  In such a case, a different ENVIRONMENT type would be used.

Do note that you first need to generate a key pair on the coordinator machine to allow the daemon to export signed archives of files from the store (see Invoking guix archive), though this step is automatic on Guix System:

     # guix archive --generate-key

Each target machine must authorize the key of the master machine so that it accepts store items it receives from the coordinator:

     # guix archive --authorize < coordinator-public-key.txt

user, in this example, specifies the name of the user account to log in as to perform the deployment.  Its default value is root, but root login over SSH may be forbidden in some cases.  To work around this, guix deploy can log in as an unprivileged user and employ sudo to escalate privileges.  This will only work if sudo is currently installed on the remote and can be invoked non-interactively as user.  That is, the line in sudoers granting user the ability to use sudo must contain the NOPASSWD tag.  This can be accomplished with the following operating system configuration snippet:

     (use-modules ...
                  (gnu system))               ;for %sudoers-specification

     (define %user "username")

     (operating-system
       ...
       (sudoers-file
          (plain-file "sudoers"
                      (string-append (plain-file-content %sudoers-specification)
                                     (format #f "~a ALL = NOPASSWD: ALL~%"
                                             %user)))))

For more information regarding the format of the sudoers file, consult man sudoers.

Once you've deployed a system on a set of machines, you may find it useful to run a command on all of them.  The --execute or -x option lets you do that; the example below runs uname -a on all the machines listed in the deployment file:

     guix deploy FILE -x -- uname -a

One thing you may often need to do after deployment is restart specific services on all the machines, which you can do like so:

     guix deploy FILE -x -- herd restart SERVICE

The guix deploy -x command returns zero if and only if the command succeeded on all the machines.

Below are the data types you need to know about when writing a deployment file.

 -- Data Type: machine
     This is the data type representing a single machine in a heterogeneous Guix deployment.

     operating-system
          The object of the operating system configuration to deploy.

     environment
          An environment-type describing how the machine should be provisioned.

     configuration (default: #f)
          An object describing the configuration for the machine's environment. If the environment has a default configuration, #f may be used. If #f is used for an environment with no default configuration, however, an error will be thrown.

 -- Data Type: machine-ssh-configuration
     This is the data type representing the SSH client parameters for a machine with an environment of managed-host-environment-type.

     host-name

     build-locally? (default: #t)
          If false, system derivations will be built on the machine being deployed to.

     system
          The system type describing the architecture of the machine being deployed to---e.g., "x86_64-linux".

     authorize? (default: #t)
          If true, the coordinator's signing key will be added to the remote's ACL keyring.

     port (default: 22)

     user (default: "root")

     identity (default: #f)
          If specified, the path to the SSH private key to use to authenticate with the remote host.

     host-key (default: #f)
          This should be the SSH host key of the machine, which looks like this:

               ssh-ed25519 AAAAC3Nz... root@example.org

          When host-key is #f, the server is authenticated against the ~/.ssh/known_hosts file, just like the OpenSSH ssh client does.

     allow-downgrades? (default: #f)
          Whether to allow potential downgrades.

          Like guix system reconfigure, guix deploy compares the channel commits currently deployed on the remote host (as returned by guix system describe) to those currently in use (as returned by guix describe) to determine whether commits currently in use are descendants of those deployed.  When this is not the case and allow-downgrades? is false, it raises an error. This ensures you do not accidentally downgrade remote machines.

     safety-checks? (default: #t)
          Whether to perform ``safety checks'' before deployment.  This includes verifying that devices and file systems referred to in the operating system configuration actually exist on the target machine, and making sure that Linux modules required to access storage devices at boot time are listed in the initrd-modules field of the operating system.

          These safety checks ensure that you do not inadvertently deploy a system that would fail to boot.  Be careful before turning them off!

 -- Data Type: digital-ocean-configuration
     This is the data type describing the Droplet that should be created for a machine with an environment of digital-ocean-environment-type.

     ssh-key
          The path to the SSH private key to use to authenticate with the remote host.  In the future, this field may not exist.

     tags
          A list of string ``tags'' that uniquely identify the machine.  Must be given such that no two machines in the deployment have the same set of tags.

     region
          A Digital Ocean region slug, such as "nyc3".

     size
          A Digital Ocean size slug, such as "s-1vcpu-1gb"

     enable-ipv6?
          Whether or not the droplet should be created with IPv6 networking.

Running Guix in a Virtual Machine
=================================

To run Guix in a virtual machine (VM), one can use the pre-built Guix VM image distributed at https://ftp.gnu.org/gnu/guix/guix-system-vm-image-VERSION.x86_64-linux.qcow2. This image is a compressed image in QCOW format.  You can pass it to an emulator such as QEMU (https://qemu.org/) (see below for details).

This image boots the Xfce graphical environment and it contains some commonly used tools.  You can install more software in the image by running guix package in a terminal (see Invoking guix package).  You can also reconfigure the system based on its initial configuration file available as /run/current-system/configuration.scm (see Using the Configuration System).

Instead of using this pre-built image, one can also build their own image using guix system image (see Invoking guix system).

If you built your own image, you must copy it out of the store (see The Store) and give yourself permission to write to the copy before you can use it.  When invoking QEMU, you must choose a system emulator that is suitable for your hardware platform.  Here is a minimal QEMU invocation that will boot the result of guix system image -t qcow2 on x86_64 hardware:

     $ qemu-system-x86_64 \
        -nic user,model=virtio-net-pci \
        -enable-kvm -m 2048 \
        -device virtio-blk,drive=myhd \
        -drive if=none,file=guix-system-vm-image-VERSION.x86_64-linux.qcow2,id=myhd

Here is what each of these options means:

qemu-system-x86_64
     This specifies the hardware platform to emulate.  This should match the host.

-nic user,model=virtio-net-pci
     Enable the unprivileged user-mode network stack.  The guest OS can access the host but not vice versa.  This is the simplest way to get the guest OS online.  model specifies which network device to emulate: virtio-net-pci is a special device made for virtualized operating systems and recommended for most uses.  Assuming your hardware platform is x86_64, you can get a list of available NIC models by running qemu-system-x86_64 -nic model=help.

-enable-kvm
     If your system has hardware virtualization extensions, enabling the virtual machine support (KVM) of the Linux kernel will make things run faster.

-m 2048
     RAM available to the guest OS, in mebibytes.  Defaults to 128 MiB, which may be insufficient for some operations.

-device virtio-blk,drive=myhd
     Create a virtio-blk drive called ``myhd''.  virtio-blk is a ``paravirtualization'' mechanism for block devices that allows QEMU to achieve better performance than if it were emulating a complete disk drive.  See the QEMU and KVM documentation for more info.

-drive if=none,file=/tmp/qemu-image,id=myhd
     Use our QCOW image, the guix-system-vm-image-VERSION.x86_64-linux.qcow2 file, as the backing store of the ``myhd'' drive.

The default run-vm.sh script that is returned by an invocation of guix system vm does not add a -nic user flag by default. To get network access from within the vm add the (dhcp-client-service) to your system definition and start the VM using $(guix system vm config.scm) -nic user.  An important caveat of using -nic user for networking is that ping will not work, because it uses the ICMP protocol.  You'll have to use a different command to check for network connectivity, for example guix download.

Connecting Through SSH
----------------------

To enable SSH inside a VM you need to add an SSH server like openssh-service-type to your VM (see openssh-service-type).  In addition you need to forward the SSH port, 22 by default, to the host.  You can do this with

     $(guix system vm config.scm) -nic user,model=virtio-net-pci,hostfwd=tcp::10022-:22

To connect to the VM you can run

     ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -p 10022 localhost

The -p tells ssh the port you want to connect to. -o UserKnownHostsFile=/dev/null prevents ssh from complaining every time you modify your config.scm file and the -o StrictHostKeyChecking=no prevents you from having to allow a connection to an unknown host every time you connect.

     If you find the above hostfwd example not to be working (e.g., your SSH client hangs attempting to connect to the mapped port of your VM), make sure that your Guix System VM has networking support, such as by using the dhcp-client-service-type service type.

Using virt-viewer with Spice
----------------------------

As an alternative to the default qemu graphical client you can use the remote-viewer from the virt-viewer package.  To connect pass the -spice port=5930,disable-ticketing flag to qemu.  See previous section for further information on how to do this.

Spice also allows you to do some nice stuff like share your clipboard with your VM.  To enable that you'll also have to pass the following flags to qemu:

     -device virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x5
     -chardev spicevmc,name=vdagent,id=vdagent
     -device virtserialport,nr=1,bus=virtio-serial0.0,chardev=vdagent,\
     name=com.redhat.spice.0

You'll also need to add the (spice-vdagent-service) to your system definition (see Spice service).

Defining Services
=================

The previous sections show the available services and how one can combine them in an operating-system declaration.  But how do we define them in the first place?  And what is a service anyway?

Service Composition
-------------------

Here we define a service as, broadly, something that extends the functionality of the operating system.  Often a service is a process---a daemon---started when the system boots: a secure shell server, a Web server, the Guix build daemon, etc.  Sometimes a service is a daemon whose execution can be triggered by another daemon---e.g., an FTP server started by inetd or a D-Bus service activated by dbus-daemon.  Occasionally, a service does not map to a daemon.  For instance, the ``account'' service collects user accounts and makes sure they exist when the system runs; the ``udev'' service collects device management rules and makes them available to the eudev daemon; the /etc service populates the /etc directory of the system.

Guix system services are connected by extensions.  For instance, the secure shell service extends the Shepherd---the initialization system, running as PID 1---by giving it the command lines to start and stop the secure shell daemon (see openssh-service-type); the UPower service extends the D-Bus service by passing it its .service specification, and extends the udev service by passing it device management rules (see upower-service); the Guix daemon service extends the Shepherd by passing it the command lines to start and stop the daemon, and extends the account service by passing it a list of required build user accounts (see Base Services).

All in all, services and their ``extends'' relations form a directed acyclic graph (DAG).  If we represent services as boxes and extensions as arrows, a typical system might provide something like this:

Typical service extension graph.

At the bottom, we see the system service, which produces the directory containing everything to run and boot the system, as returned by the guix system build command.  See Service Reference, to learn about the other service types shown here. See the guix system extension-graph command, for information on how to generate this representation for a particular operating system definition.

Technically, developers can define service types to express these relations.  There can be any number of services of a given type on the system---for instance, a system running two instances of the GNU secure shell server (lsh) has two instances of lsh-service-type, with different parameters.

The following section describes the programming interface for service types and services.

Service Types and Services
--------------------------

A service type is a node in the DAG described above.  Let us start with a simple example, the service type for the Guix build daemon (see Invoking guix-daemon):

     (define guix-service-type
       (service-type
        (name 'guix)
        (extensions
         (list (service-extension shepherd-root-service-type guix-shepherd-service)
               (service-extension account-service-type guix-accounts)
               (service-extension activation-service-type guix-activation)))
        (default-value (guix-configuration))))

It defines three things:

 1. A name, whose sole purpose is to make inspection and debugging easier.

 2. A list of service extensions, where each extension designates the target service type and a procedure that, given the parameters of the service, returns a list of objects to extend the service of that type.

     Every service type has at least one service extension.  The only exception is the boot service type, which is the ultimate service.

 3. Optionally, a default value for instances of this type.

In this example, guix-service-type extends three services:

shepherd-root-service-type
     The guix-shepherd-service procedure defines how the Shepherd service is extended.  Namely, it returns a <shepherd-service> object that defines how guix-daemon is started and stopped (see Shepherd Services).

account-service-type
     This extension for this service is computed by guix-accounts, which returns a list of user-group and user-account objects representing the build user accounts (see Invoking guix-daemon).

activation-service-type
     Here guix-activation is a procedure that returns a gexp, which is a code snippet to run at ``activation time''---e.g., when the service is booted.

A service of this type is instantiated like this:

     (service guix-service-type
              (guix-configuration
                (build-accounts 5)
                (extra-options '("--gc-keep-derivations"))))

The second argument to the service form is a value representing the parameters of this specific service instance. See guix-configuration, for information about the guix-configuration data type.  When the value is omitted, the default value specified by guix-service-type is used:

     (service guix-service-type)

guix-service-type is quite simple because it extends other services but is not extensible itself.

The service type for an extensible service looks like this:

     (define udev-service-type
       (service-type (name 'udev)
                     (extensions
                      (list (service-extension shepherd-root-service-type
                                               udev-shepherd-service)))

                     (compose concatenate)       ;concatenate the list of rules
                     (extend (lambda (config rules)
                               (udev-configuration
                                (inherit config)
                                (rules (append (udev-configuration-rules config)
                                               rules)))))))

This is the service type for the eudev device management daemon (https://github.com/eudev-project/eudev).  Compared to the previous example, in addition to an extension of shepherd-root-service-type, we see two new fields:

compose
     This is the procedure to compose the list of extensions to services of this type.

     Services can extend the udev service by passing it lists of rules; we compose those extensions simply by concatenating them.

extend
     This procedure defines how the value of the service is extended with the composition of the extensions.

     Udev extensions are composed into a list of rules, but the udev service value is itself a <udev-configuration> record.  So here, we extend that record by appending the list of rules it contains to the list of contributed rules.

description
     This is a string giving an overview of the service type.  The string can contain Texinfo markup (see Overview (GNU Texinfo)).  The guix system search command searches these strings and displays them (see Invoking guix system).

There can be only one instance of an extensible service type such as udev-service-type.  If there were more, the service-extension specifications would be ambiguous.

Still here?  The next section provides a reference of the programming interface for services.

Service Reference
-----------------

We have seen an overview of service types (see Service Types and Services).  This section provides a reference on how to manipulate services and service types.  This interface is provided by the (gnu services) module.

 -- Procedure: service type [value]
     Return a new service of TYPE, a <service-type> object (see below).  VALUE can be any object; it represents the parameters of this particular service instance.

     When VALUE is omitted, the default value specified by TYPE is used; if TYPE does not specify a default value, an error is raised.

     For instance, this:

          (service openssh-service-type)

     is equivalent to this:

          (service openssh-service-type
                   (openssh-configuration))

     In both cases the result is an instance of openssh-service-type with the default configuration.

 -- Procedure: service? obj
     Return true if OBJ is a service.

 -- Procedure: service-kind service
     Return the type of SERVICE---i.e., a <service-type> object.

 -- Procedure: service-value service
     Return the value associated with SERVICE.  It represents its parameters.

Here is an example of how a service is created and manipulated:

     (define s
       (service nginx-service-type
                (nginx-configuration
                 (nginx nginx)
                 (log-directory log-directory)
                 (run-directory run-directory)
                 (file config-file))))

     (service? s)
     => #t

     (eq? (service-kind s) nginx-service-type)
     => #t

The modify-services form provides a handy way to change the parameters of some of the services of a list such as %base-services (see %base-services).  It evaluates to a list of services.  Of course, you could always use standard list combinators such as map and fold to do that (see List Library (GNU Guile Reference Manual)); modify-services simply provides a more concise form for this common pattern.

 -- Special Form: modify-services services
     (type variable => body) ...

     Modify the services listed in SERVICES according to the given clauses.  Each clause has the form:

          (TYPE VARIABLE => BODY)

     where TYPE is a service type---e.g., guix-service-type---and VARIABLE is an identifier that is bound within the BODY to the service parameters---e.g., a guix-configuration instance---of the original service of that TYPE.

     The BODY should evaluate to the new service parameters, which will be used to configure the new service.  This new service will replace the original in the resulting list.  Because a service's service parameters are created using define-record-type*, you can write a succinct BODY that evaluates to the new service parameters by using the inherit feature that define-record-type* provides.

     Clauses can also have the following form:

          (delete TYPE)

     Such a clause removes all services of the given TYPE from SERVICES.

     See Using the Configuration System, for example usage.

Next comes the programming interface for service types.  This is something you want to know when writing new service definitions, but not necessarily when simply looking for ways to customize your operating-system declaration.

 -- Data Type: service-type
     This is the representation of a service type (see Service Types and Services).

     name
          This is a symbol, used only to simplify inspection and debugging.

     extensions
          A non-empty list of <service-extension> objects (see below).

     compose (default: #f)
          If this is #f, then the service type denotes services that cannot be extended---i.e., services that do not receive ``values'' from other services.

          Otherwise, it must be a one-argument procedure.  The procedure is called by fold-services and is passed a list of values collected from extensions.  It may return any single value.

     extend (default: #f)
          If this is #f, services of this type cannot be extended.

          Otherwise, it must be a two-argument procedure: fold-services calls it, passing it the initial value of the service as the first argument and the result of applying compose to the extension values as the second argument.  It must return a value that is a valid parameter value for the service instance.

     description
          This is a string, possibly using Texinfo markup, describing in a couple of sentences what the service is about.  This string allows users to find about the service through guix system search (see Invoking guix system).

     default-value (default: &no-default-value)
          The default value associated for instances of this service type.  This allows users to use the service form without its second argument:

               (service TYPE)

          The returned service in this case has the default value specified by TYPE.

     See Service Types and Services, for examples.

 -- Procedure: service-extension target-type compute
     Return a new extension for services of type TARGET-TYPE. COMPUTE must be a one-argument procedure: fold-services calls it, passing it the value associated with the service that provides the extension; it must return a valid value for the target service.

 -- Procedure: service-extension? obj
     Return true if OBJ is a service extension.

Occasionally, you might want to simply extend an existing service.  This involves creating a new service type and specifying the extension of interest, which can be verbose; the simple-service procedure provides a shorthand for this.

 -- Procedure: simple-service name target value
     Return a service that extends TARGET with VALUE.  This works by creating a singleton service type NAME, of which the returned service is an instance.

     For example, this extends mcron (see Scheduled Job Execution) with an additional job:

          (simple-service 'my-mcron-job mcron-service-type
                          #~(job '(next-hour (3)) "guix gc -F 2G"))

At the core of the service abstraction lies the fold-services procedure, which is responsible for ``compiling'' a list of services down to a single directory that contains everything needed to boot and run the system---the directory shown by the guix system build command (see Invoking guix system).  In essence, it propagates service extensions down the service graph, updating each node parameters on the way, until it reaches the root node.

 -- Procedure: fold-services services [#:target-type system-service-type]
     Fold SERVICES by propagating their extensions down to the root of type TARGET-TYPE; return the root service adjusted accordingly.

Lastly, the (gnu services) module also defines several essential service types, some of which are listed below.

 -- Variable: system-service-type
     This is the root of the service graph.  It produces the system directory as returned by the guix system build command.

 -- Variable: boot-service-type
     The type of the ``boot service'', which produces the boot script. The boot script is what the initial RAM disk runs when booting.

 -- Variable: etc-service-type
     The type of the /etc service.  This service is used to create files under /etc and can be extended by passing it name/file tuples such as:

          (list `("issue" ,(plain-file "issue" "Welcome!\n")))

     In this example, the effect would be to add an /etc/issue file pointing to the given file.

 -- Variable: setuid-program-service-type
     Type for the ``setuid-program service''.  This service collects lists of executable file names, passed as gexps, and adds them to the set of setuid and setgid programs on the system (see Setuid Programs).

 -- Variable: profile-service-type
     Type of the service that populates the system profile---i.e., the programs under /run/current-system/profile.  Other services can extend it by passing it lists of packages to add to the system profile.

 -- Variable: provenance-service-type
     This is the type of the service that records provenance meta-data in the system itself.  It creates several files under /run/current-system:

     channels.scm
          This is a ``channel file'' that can be passed to guix pull -C or guix time-machine -C, and which describes the channels used to build the system, if that information was available (see Channels).

     configuration.scm
          This is the file that was passed as the value for this provenance-service-type service.  By default, guix system reconfigure automatically passes the OS configuration file it received on the command line.

     provenance
          This contains the same information as the two other files but in a format that is more readily processable.

     In general, these two pieces of information (channels and configuration file) are enough to reproduce the operating system ``from source''.

          This information is necessary to rebuild your operating system, but it is not always sufficient.  In particular, configuration.scm itself is insufficient if it is not self-contained---if it refers to external Guile modules or to extra files.  If you want configuration.scm to be self-contained, we recommend that modules or files it refers to be part of a channel.

          Besides, provenance meta-data is ``silent'' in the sense that it does not change the bits contained in your system, except for the meta-data bits themselves.  Two different OS configurations or sets of channels can lead to the same system, bit-for-bit; when provenance-service-type is used, these two systems will have different meta-data and thus different store file names, which makes comparison less trivial.

     This service is automatically added to your operating system configuration when you use guix system reconfigure, guix system init, or guix deploy.

 -- Variable: linux-loadable-module-service-type
     Type of the service that collects lists of packages containing kernel-loadable modules, and adds them to the set of kernel-loadable modules.

     This service type is intended to be extended by other service types, such as below:

          (simple-service 'installing-module
                          linux-loadable-module-service-type
                          (list module-to-install-1
                                module-to-install-2))

     This does not actually load modules at bootup, only adds it to the kernel profile so that it can be loaded by other means.

Shepherd Services
-----------------

The (gnu services shepherd) module provides a way to define services managed by the GNU Shepherd, which is the initialization system---the first process that is started when the system boots, also known as PID 1 (see Introduction (The GNU Shepherd Manual)).

Services in the Shepherd can depend on each other.  For instance, the SSH daemon may need to be started after the syslog daemon has been started, which in turn can only happen once all the file systems have been mounted.  The simple operating system defined earlier (see Using the Configuration System) results in a service graph like this:

Typical shepherd service graph.

You can actually generate such a graph for any operating system definition using the guix system shepherd-graph command (see guix system shepherd-graph).

The %shepherd-root-service is a service object representing PID 1, of type shepherd-root-service-type; it can be extended by passing it lists of <shepherd-service> objects.

 -- Data Type: shepherd-service
     The data type representing a service managed by the Shepherd.

     provision
          This is a list of symbols denoting what the service provides.

          These are the names that may be passed to herd start, herd status, and similar commands (see Invoking herd (The GNU Shepherd Manual)).  See Defining Services (The GNU Shepherd Manual), for details.

     requirement (default: '())
          List of symbols denoting the Shepherd services this one depends on.

     one-shot? (default: #f)
          Whether this service is one-shot.  One-shot services stop immediately after their start action has completed.  See Slots of services (The GNU Shepherd Manual), for more info.

     respawn? (default: #t)
          Whether to restart the service when it stops, for instance when the underlying process dies.

     respawn-limit (default: #f)
          Set a limit on how many times and how frequently a service may be restarted by Shepherd before it is disabled.  See Defining Services (The GNU Shepherd Manual), for details.

     respawn-delay (default: #f)
          When true, this is the delay in seconds before restarting a failed service.

     start
     stop (default: #~(const #f))
          The start and stop fields refer to the Shepherd's facilities to start and stop processes (see Service De- and Constructors (The GNU Shepherd Manual)).  They are given as G-expressions that get expanded in the Shepherd configuration file (see G-Expressions).

     actions (default: '())
          This is a list of shepherd-action objects (see below) defining actions supported by the service, in addition to the standard start and stop actions.  Actions listed here become available as herd sub-commands:

               herd ACTION SERVICE [ARGUMENTS...]

     auto-start? (default: #t)
          Whether this service should be started automatically by the Shepherd.  If it is #f the service has to be started manually with herd start.

     documentation
          A documentation string, as shown when running:

               herd doc SERVICE-NAME

          where SERVICE-NAME is one of the symbols in provision (see Invoking herd (The GNU Shepherd Manual)).

     modules (default: %default-modules)
          This is the list of modules that must be in scope when start and stop are evaluated.

The example below defines a Shepherd service that spawns syslogd, the system logger from the GNU Networking Utilities (see syslogd (GNU Inetutils)):

     (let ((config (plain-file "syslogd.conf" "...")))
       (shepherd-service
         (documentation "Run the syslog daemon (syslogd).")
         (provision '(syslogd))
         (requirement '(user-processes))
         (start #~(make-forkexec-constructor
                    (list #$(file-append inetutils "/libexec/syslogd")
                          "--rcfile" #$config)
                    #:pid-file "/var/run/syslog.pid"))
         (stop #~(make-kill-destructor))))

Key elements in this example are the start and stop fields: they are staged code snippets that use the make-forkexec-constructor procedure provided by the Shepherd and its dual, make-kill-destructor (see Service De- and Constructors (The GNU Shepherd Manual)).  The start field will have shepherd spawn syslogd with the given option; note that we pass config after --rcfile, which is a configuration file declared above (contents of this file are omitted).  Likewise, the stop field tells how this service is to be stopped; in this case, it is stopped by making the kill system call on its PID.  Code staging is achieved using G-expressions: #~ stages code, while #$ ``escapes'' back to host code (see G-Expressions).

 -- Data Type: shepherd-action
     This is the data type that defines additional actions implemented by a Shepherd service (see above).

     name
          Symbol naming the action.

     documentation
          This is a documentation string for the action.  It can be viewed by running:

               herd doc SERVICE action ACTION

     procedure
          This should be a gexp that evaluates to a procedure of at least one argument, which is the ``running value'' of the service (see Slots of services (The GNU Shepherd Manual)).

     The following example defines an action called say-hello that kindly greets the user:

          (shepherd-action
            (name 'say-hello)
            (documentation "Say hi!")
            (procedure #~(lambda (running . args)
                           (format #t "Hello, friend! arguments: ~s\n"
                                   args)
                           #t)))

     Assuming this action is added to the example service, then you can do:

          # herd say-hello example
          Hello, friend! arguments: ()
          # herd say-hello example a b c
          Hello, friend! arguments: ("a" "b" "c")

     This, as you can see, is a fairly sophisticated way to say hello. See Defining Services (The GNU Shepherd Manual), for more info on actions.

 -- Procedure: shepherd-configuration-action
     Return a configuration action to display FILE, which should be the name of the service's configuration file.

     It can be useful to equip services with that action.  For example, the service for the Tor anonymous router (see tor-service-type) is defined roughly like this:

          (let ((torrc (plain-file "torrc" ...)))
            (shepherd-service
              (provision '(tor))
              (requirement '(user-processes loopback syslogd))

              (start #~(make-forkexec-constructor
                        (list #$(file-append tor "/bin/tor") "-f" #$torrc)
                        #:user "tor" #:group "tor"))
              (stop #~(make-kill-destructor))
              (actions (list (shepherd-configuration-action torrc)))
              (documentation "Run the Tor anonymous network overlay.")))

     Thanks to this action, administrators can inspect the configuration file passed to tor with this shell command:

          cat $(herd configuration tor)

     This can come in as a handy debugging tool!

 -- Variable: shepherd-root-service-type
     The service type for the Shepherd ``root service''---i.e., PID 1.

     This is the service type that extensions target when they want to create shepherd services (see Service Types and Services, for an example). Each extension must pass a list of <shepherd-service>.  Its value must be a shepherd-configuration, as described below.

 -- Data Type: shepherd-configuration
     This data type represents the Shepherd's configuration.

     shepherd (default: shepherd)
          The Shepherd package to use.

     services (default: '())
          A list of <shepherd-service> to start. You should probably use the service extension mechanism instead (see Shepherd Services).

The following example specifies the Shepherd package for the operating system:

     (operating-system
       ;; ...
       (services (append (list openssh-service-type))
                 ;; ...
                 %desktop-services)
       ;; ...
       ;; Use own Shepherd package.
       (essential-services
        (modify-services (operating-system-default-essential-services
                          this-operating-system)
          (shepherd-root-service-type config => (shepherd-configuration
                                                 (inherit config)
                                                 (shepherd my-shepherd))))))

 -- Variable: %shepherd-root-service
     This service represents PID 1.

Complex Configurations
----------------------

Some programs might have rather complex configuration files or formats, and to make it easier to create Scheme bindings for these configuration files, you can use the utilities defined in the (gnu services configuration) module.

The main utility is the define-configuration macro, a helper used to define a Scheme record type (see Record Overview (GNU Guile Reference Manual)).  The fields from this Scheme record can be serialized using serializers, which are procedures that take some kind of Scheme value and translates them into another Scheme value or G-Expressions.

 -- Macro: define-configuration name clause1 clause2 ...
     Create a record type named NAME that contains the fields found in the clauses.

     A clause has the following form:

          (FIELD-NAME
           TYPE-DECL
           DOCUMENTATION
           OPTION*
           ...)

     FIELD-NAME is an identifier that denotes the name of the field in the generated record.

     TYPE-DECL is either TYPE for fields that require a value to be set or (TYPE DEFAULT-VALUE) otherwise.

     TYPE is the type of the value corresponding to FIELD-NAME; since Guile is untyped, a predicate procedure---TYPE?---will be called on the value corresponding to the field to ensure that the value is of the correct type.  This means that if say, TYPE is package, then a procedure named package? will be applied on the value to make sure that it is indeed a <package> object.

     DEFAULT-VALUE is the default value corresponding to the field; if none is specified, the user is forced to provide a value when creating an object of the record type.

     DOCUMENTATION is a string formatted with Texinfo syntax which should provide a description of what setting this field does.

     OPTION* is one of the following subclauses:

     empty-serializer
          Exclude this field from serialization.

     (serializer SERIALIZER)
          SERIALIZER is the name of a procedure which takes two arguments, the first is the name of the field, and the second is the value corresponding to the field.  The procedure should return a string or G-Expressions that represents the content that will be serialized to the configuration file.  If none is specified, a procedure of the name serialize-TYPE will be used.

          An example of a simple serializer procedure:

               (define (serialize-boolean field-name value)
                 (let ((value (if value "true" "false")))
                   #~(string-append '#$field-name " = " #$value)))

     (sanitizer SANITIZER)
          SANITIZER is a procedure which takes one argument, a user-supplied value, and returns a ``sanitized'' value for the field. If no sanitizer is specified, a default sanitizer is used, which raises an error if the value is not of type TYPE.

          An example of a sanitizer for a field that accepts both strings and symbols looks like this:

               (define (sanitize-foo value)
                 (cond ((string? value) value)
                       ((symbol? value) (symbol->string value))
                       (else (error "bad value"))))

     In some cases multiple different configuration records might be defined in the same file, but their serializers for the same type might have to be different, because they have different configuration formats.  For example, the serialize-boolean procedure for the Getmail service would have to be different from the one for the Transmission service.  To make it easier to deal with this situation, one can specify a serializer prefix by using the prefix literal in the define-configuration form.  This means that one doesn't have to manually specify a custom SERIALIZER for every field.

          (define (foo-serialize-string field-name value)
            ...)

          (define (bar-serialize-string field-name value)
            ...)

          (define-configuration foo-configuration
            (label
             string
             "The name of label.")
            (prefix foo-))

          (define-configuration bar-configuration
            (ip-address
             string
             "The IPv4 address for this device.")
            (prefix bar-))

     However, in some cases you might not want to serialize any of the values of the record, to do this, you can use the no-serialization literal.  There is also the define-configuration/no-serialization macro which is a shorthand of this.

          ;; Nothing will be serialized to disk.
          (define-configuration foo-configuration
            (field
             (string "test")
             "Some documentation.")
            (no-serialization))

          ;; The same thing as above.
          (define-configuration/no-serialization bar-configuration
            (field
             (string "test")
             "Some documentation."))

 -- Macro: define-maybe type
     Sometimes a field should not be serialized if the user doesn’t specify a value.  To achieve this, you can use the define-maybe macro to define a ``maybe type''; if the value of a maybe type is left unset, or is set to the %unset-value value, then it will not be serialized.

     When defining a ``maybe type'', the corresponding serializer for the regular type will be used by default.  For example, a field of type maybe-string will be serialized using the serialize-string procedure by default, you can of course change this by specifying a custom serializer procedure.  Likewise, the type of the value would have to be a string, or left unspecified.

          (define-maybe string)

          (define (serialize-string field-name value)
            ...)

          (define-configuration baz-configuration
            (name
             ;; If set to a string, the `serialize-string' procedure will be used
             ;; to serialize the string.  Otherwise this field is not serialized.
             maybe-string
             "The name of this module."))

     Like with define-configuration, one can set a prefix for the serializer name by using the prefix literal.

          (define-maybe integer
            (prefix baz-))

          (define (baz-serialize-integer field-name value)
            ...)

     There is also the no-serialization literal, which when set means that no serializer will be defined for the ``maybe type'', regardless of whether its value is set or not. define-maybe/no-serialization is a shorthand for specifying the no-serialization literal.

          (define-maybe/no-serialization symbol)

          (define-configuration/no-serialization test-configuration
            (mode
             maybe-symbol
             "Docstring."))

 -- Procedure: maybe-value-set? value
     Predicate to check whether a user explicitly specified the value of a maybe field.

 -- Procedure: serialize-configuration configuration fields
     Return a G-expression that contains the values corresponding to the FIELDS of CONFIGURATION, a record that has been generated by define-configuration.  The G-expression can then be serialized to disk by using something like mixed-text-file.

Once you have defined a configuration record, you will most likely also want to document it so that other people know to use it.  To help with that, there are two procedures, both of which are documented below.

 -- Procedure: generate-documentation documentation documentation-name
     Generate a Texinfo fragment from the docstrings in DOCUMENTATION, a list of (LABEL FIELDS SUB-DOCUMENTATION ...). LABEL should be a symbol and should be the name of the configuration record.  FIELDS should be a list of all the fields available for the configuration record.

     SUB-DOCUMENTATION is a (FIELD-NAME CONFIGURATION-NAME) tuple.  FIELD-NAME is the name of the field which takes another configuration record as its value, and CONFIGURATION-NAME is the name of that configuration record.

     SUB-DOCUMENTATION is only needed if there are nested configuration records.  For example, the getmail-configuration record (see Mail Services) accepts a getmail-configuration-file record in one of its rcfile field, therefore documentation for getmail-configuration-file is nested in getmail-configuration.

          (generate-documentation
            `((getmail-configuration ,getmail-configuration-fields
               (rcfile getmail-configuration-file))
              ...)
            'getmail-configuration)

     DOCUMENTATION-NAME should be a symbol and should be the name of the configuration record.

 -- Procedure: configuration->documentation configuration-symbol
     Take CONFIGURATION-SYMBOL, the symbol corresponding to the name used when defining a configuration record with define-configuration, and print the Texinfo documentation of its fields.  This is useful if there aren’t any nested configuration records since it only prints the documentation for the top-level fields.

As of right now, there is no automated way to generate documentation for configuration records and put them in the manual.  Instead, every time you make a change to the docstrings of a configuration record, you have to manually call generate-documentation or configuration->documentation, and paste the output into the doc/guix.texi file.

Below is an example of a record type created using define-configuration and friends.

     (use-modules (gnu services)
                  (guix gexp)
                  (gnu services configuration)
                  (srfi srfi-26)
                  (srfi srfi-1))

     ;; Turn field names, which are Scheme symbols into strings
     (define (uglify-field-name field-name)
       (let ((str (symbol->string field-name)))
         ;; field? -> is-field
         (if (string-suffix? "?" str)
             (string-append "is-" (string-drop-right str 1))
             str)))

     (define (serialize-string field-name value)
       #~(string-append #$(uglify-field-name field-name) " = " #$value "\n"))

     (define (serialize-integer field-name value)
       (serialize-string field-name (number->string value)))

     (define (serialize-boolean field-name value)
       (serialize-string field-name (if value "true" "false")))

     (define (serialize-contact-name field-name value)
       #~(string-append "\n[" #$value "]\n"))

     (define (list-of-contact-configurations? lst)
       (every contact-configuration? lst))

     (define (serialize-list-of-contact-configurations field-name value)
       #~(string-append #$@(map (cut serialize-configuration <>
                                     contact-configuration-fields)
                                value)))

     (define (serialize-contacts-list-configuration configuration)
       (mixed-text-file
        "contactrc"
        #~(string-append "[Owner]\n"
                         #$(serialize-configuration
                            configuration contacts-list-configuration-fields))))

     (define-maybe integer)
     (define-maybe string)

     (define-configuration contact-configuration
       (name
        string
        "The name of the contact."
        serialize-contact-name)
       (phone-number
        maybe-integer
        "The person's phone number.")
       (email
        maybe-string
        "The person's email address.")
       (married?
        boolean
        "Whether the person is married."))

     (define-configuration contacts-list-configuration
       (name
        string
        "The name of the owner of this contact list.")
       (email
        string
        "The owner's email address.")
       (contacts
        (list-of-contact-configurations '())
        "A list of @code{contact-configuation} records which contain
     information about all your contacts."))

A contacts list configuration could then be created like this:

     (define my-contacts
       (contacts-list-configuration
        (name "Alice")
        (email "alice@example.org")
        (contacts
         (list (contact-configuration
                (name "Bob")
                (phone-number 1234)
                (email "bob@gnu.org")
                (married? #f))
               (contact-configuration
                (name "Charlie")
                (phone-number 0000)
                (married? #t))))))

After serializing the configuration to disk, the resulting file would look like this:

     [owner]
     name = Alice
     email = alice@example.org

     [Bob]
     phone-number = 1234
     email = bob@gnu.org
     is-married = false

     [Charlie]
     phone-number = 0
     is-married = true

System Troubleshooting Tips
***************************

Guix System allows rebooting into a previous generation should the last one be malfunctioning, which makes it quite robust against being broken irreversibly.  This feature depends on GRUB being correctly functioning though, which means that if for whatever reasons your GRUB installation becomes corrupted during a system reconfiguration, you may not be able to easily boot into a previous generation.  A technique that can be used in this case is to chroot into your broken system and reconfigure it from there.  Such technique is explained below.

Chrooting into an existing system
=================================

This section details how to chroot to an already installed Guix System with the aim of reconfiguring it, for example to fix a broken GRUB installation.  The process is similar to how it would be done on other GNU/Linux systems, but there are some Guix System particularities such as the daemon and profiles that make it worthy of explaining here.

 1. Obtain a bootable image of Guix System.  It is recommended the latest development snapshot so the kernel and the tools used are at least as as new as those of your installed system; it can be retrieved from the https://ci.guix.gnu.org (https://ci.guix.gnu.org/search/latest/ISO-9660?query=spec:images+status:success+system:x86_64-linux+image.iso) URL.  Follow the see USB Stick and DVD Installation section for copying it to a bootable media.

 2. Boot the image, and proceed with the graphical text-based installer until your network is configured.  Alternatively, you could configure the network manually by following the manual-installation-networking section.  If you get the error RTNETLINK answers: Operation not possible due to RF-kill, try rfkill list followed by rfkill unblock 0, where 0 is your device identifier (ID).

 3. Switch to a virtual console (tty) if you haven't already by pressing simultaneously the Control + Alt + F4 keys.  Mount your file system at /mnt.  Assuming your root partition is /dev/sda2, you would do:

          mount /dev/sda2 /mnt

 4. Mount special block devices and Linux-specific directories:

          mount --rbind /proc /mnt/proc
          mount --rbind /sys /mnt/sys
          mount --rbind /dev /mnt/dev

     If your system is EFI-based, you must also mount the ESP partition. Assuming it is /dev/sda1, you can do so with:

          mount /dev/sda1 /mnt/boot/efi

 5. Enter your system via chroot:

          chroot /mnt /bin/sh

 6. Source the system profile as well as your USER profile to setup the environment, where USER is the user name used for the Guix System you are attempting to repair:

          source /var/guix/profiles/system/profile/etc/profile
          source /home/USER/.guix-profile/etc/profile

     To ensure you are working with the Guix revision you normally would as your normal user, also source your current Guix profile:

          source /home/USER/.config/guix/current/etc/profile

 7. Start a minimal guix-daemon in the background:

          guix-daemon --build-users-group=guixbuild --disable-chroot &

 8. Edit your Guix System configuration if needed, then reconfigure with:

          guix system reconfigure your-config.scm

 9. Finally, you should be good to reboot the system to test your fix.

Home Configuration
******************

Guix supports declarative configuration of home environments by utilizing the configuration mechanism described in the previous chapter (see Defining Services), but for user's dotfiles and packages.  It works both on Guix System and foreign distros and allows users to declare all the packages and services that should be installed and configured for the user.  Once a user has written a file containing a home-environment record, such a configuration can be instantiated by an unprivileged user with the guix home command (see Invoking guix home).

The user's home environment usually consists of three basic parts: software, configuration, and state.  Software in mainstream distros are usually installed system-wide, but with GNU Guix most software packages can be installed on a per-user basis without needing root privileges, and are thus considered part of the user’s home environment. Packages on their own are not very useful in many cases, because often they require some additional configuration, usually config files that reside in XDG_CONFIG_HOME (~/.config by default) or other directories.  Everything else can be considered state, like media files, application databases, and logs.

Using Guix for managing home environments provides a number of advantages:

  * All software can be configured in one language (Guile Scheme), this gives users the ability to share values between configurations of different programs.

  * A well-defined home environment is self-contained and can be created in a declarative and reproducible way---there is no need to grab external binaries or manually edit some configuration file.

  * After every guix home reconfigure invocation, a new home environment generation will be created.  This means that users can rollback to a previous home environment generation so they don’t have to worry about breaking their configuration.

  * It is possible to manage stateful data with Guix Home, this includes the ability to automatically clone Git repositories on the initial setup of the machine, and periodically running commands like rsync to sync data with another host.  This functionality is still in an experimental stage, though.

Declaring the Home Environment
==============================

The home environment is configured by providing a home-environment declaration in a file that can be passed to the guix home command (see Invoking guix home).  The easiest way to get started is by generating an initial configuration with guix home import:

     guix home import ~/src/guix-config

The guix home import command reads some of the ``dot files'' such as ~/.bashrc found in your home directory and copies them to the given directory, ~/src/guix-config in this case; it also reads the contents of your profile, ~/.guix-profile, and, based on that, it populates ~/src/guix-config/home-configuration.scm with a Home configuration that resembles your current configuration.

A simple setup can include Bash and a custom text configuration, like in the example below.  Don't be afraid to declare home environment parts, which overlaps with your current dot files: before installing any configuration files, Guix Home will back up existing config files to a separate place in the home directory.

     It is highly recommended that you manage your shell or shells with Guix Home, because it will make sure that all the necessary scripts are sourced by the shell configuration file.  Otherwise you will need to do it manually. (see Configuring the Shell).

          [file he-config-bare-bones.scm not included]

The packages field should be self-explanatory, it will install the list of packages into the user's profile.  The most important field is services, it contains a list of home services, which are the basic building blocks of a home environment.

There is no daemon (at least not necessarily) related to a home service, a home service is just an element that is used to declare part of home environment and extend other parts of it.  The extension mechanism discussed in the previous chapter (see Defining Services) should not be confused with Shepherd services (see Shepherd Services).  Using this extension mechanism and some Scheme code that glues things together gives the user the freedom to declare their own, very custom, home environments.

Once the configuration looks good, you can first test it in a throw-away ``container'':

     guix home container config.scm

The command above spawns a shell where your home environment is running. The shell runs in a container, meaning it's isolated from the rest of the system, so it's a good way to try out your configuration---you can see if configuration bits are missing or misbehaving, if daemons get started, and so on.  Once you exit that shell, you're back to the prompt of your original shell ``in the real world''.

Once you have a configuration file that suits your needs, you can reconfigure your home by running:

     guix home reconfigure config.scm

This ``builds'' your home environment and creates ~/.guix-home pointing to it.  Voilà!

     Make sure the operating system has elogind, systemd, or a similar mechanism to create the XDG run-time directory and has the XDG_RUNTIME_DIR variable set.  Failing that, the on-first-login script will not execute anything, and processes like user Shepherd and its descendants will not start.

Configuring the Shell
=====================

This section is safe to skip if your shell or shells are managed by Guix Home.  Otherwise, read it carefully.

There are a few scripts that must be evaluated by a login shell to activate the home environment.  The shell startup files only read by login shells often have profile suffix.  For more information about login shells see Invoking Bash (The GNU Bash Reference Manual) and see Bash Startup Files (The GNU Bash Reference Manual).

The first script that needs to be sourced is setup-environment, which sets all the necessary environment variables (including variables declared by the user) and the second one is on-first-login, which starts Shepherd for the current user and performs actions declared by other home services that extends home-run-on-first-login-service-type.

Guix Home will always create ~/.profile, which contains the following lines:

     HOME_ENVIRONMENT=$HOME/.guix-home
     . $HOME_ENVIRONMENT/setup-environment
     $HOME_ENVIRONMENT/on-first-login

This makes POSIX compliant login shells activate the home environment. However, in most cases this file won't be read by most modern shells, because they are run in non POSIX mode by default and have their own *profile startup files.  For example Bash will prefer ~/.bash_profile in case it exists and only if it doesn't will it fallback to ~/.profile.  Zsh (if no additional options are specified) will ignore ~/.profile, even if ~/.zprofile doesn't exist.

To make your shell respect ~/.profile, add . ~/.profile or source ~/.profile to the startup file for the login shell.  In case of Bash, it is ~/.bash_profile, and in case of Zsh, it is ~/.zprofile.

     This step is only required if your shell is not managed by Guix Home. Otherwise, everything will be done automatically.

Home Services
=============

A home service is not necessarily something that has a daemon and is managed by Shepherd (see Jump Start (The GNU Shepherd Manual)), in most cases it doesn't.  It's a simple building block of the home environment, often declaring a set of packages to be installed in the home environment profile, a set of config files to be symlinked into XDG_CONFIG_HOME (~/.config by default), and environment variables to be set by a login shell.

There is a service extension mechanism (see Service Composition) which allows home services to extend other home services and utilize capabilities they provide; for example: declare mcron jobs (see GNU Mcron) by extending Mcron Home Service; declare daemons by extending Shepherd Home Service; add commands, which will be invoked on by the Bash by extending home-bash-service-type.

A good way to discover available home services is using the guix home search command (see Invoking guix home).  After the required home services are found, include its module with the use-modules form (see Using Guile Modules (The GNU Guile Reference Manual)), or the #:use-modules directive (see Creating Guile Modules (The GNU Guile Reference Manual)) and declare a home service using the service function, or extend a service type by declaring a new service with the simple-service procedure from (gnu services).

Essential Home Services
-----------------------

There are a few essential home services defined in (gnu home services), they are mostly for internal use and are required to build a home environment, but some of them will be useful for the end user.

 -- Variable: home-environment-variables-service-type
     The service of this type will be instantiated by every home environment automatically by default, there is no need to define it, but someone may want to extend it with a list of pairs to set some environment variables.

          (list ("ENV_VAR1" . "value1")
                ("ENV_VAR2" . "value2"))

     The easiest way to extend a service type, without defining a new service type is to use the simple-service helper from (gnu services).

          (simple-service 'some-useful-env-vars-service
          		home-environment-variables-service-type
          		`(("LESSHISTFILE" . "$XDG_CACHE_HOME/.lesshst")
                            ("SHELL" . ,(file-append zsh "/bin/zsh"))
                            ("USELESS_VAR" . #f)
                            ("_JAVA_AWT_WM_NONREPARENTING" . #t)
                            ("LITERAL_VALUE" . ,(literal-string "${abc}"))))

     If you include such a service in you home environment definition, it will add the following content to the setup-environment script (which is expected to be sourced by the login shell):

          export LESSHISTFILE="$XDG_CACHE_HOME/.lesshst"
          export SHELL="/gnu/store/2hsg15n644f0glrcbkb1kqknmmqdar03-zsh-5.8/bin/zsh"
          export _JAVA_AWT_WM_NONREPARENTING
          export LITERAL_VALUE='${abc}'

     Notice that literal-string above lets us declare that a value is to be interpreted as a literal string, meaning that ``special characters'' such as the dollar sign will not be interpreted by the shell.

          Make sure that module (gnu packages shells) is imported with use-modules or any other way, this namespace contains the definition of the zsh package, which is used in the example above.

     The association list (see Association Lists (The GNU Guile Reference manual)) is a data structure containing key-value pairs, for home-environment-variables-service-type the key is always a string, the value can be a string, string-valued gexp (see G-Expressions), file-like object (see file-like object) or boolean.  For gexps, the variable will be set to the value of the gexp; for file-like objects, it will be set to the path of the file in the store (see The Store); for #t, it will export the variable without any value; and for #f, it will omit variable.

 -- Variable: home-profile-service-type
     The service of this type will be instantiated by every home environment automatically, there is no need to define it, but you may want to extend it with a list of packages if you want to install additional packages into your profile.  Other services, which need to make some programs available to the user will also extend this service type.

     The extension value is just a list of packages:

          (list htop vim emacs)

     The same approach as simple-service (see simple-service) for home-environment-variables-service-type can be used here, too.  Make sure that modules containing the specified packages are imported with use-modules.  To find a package or information about its module use guix search (see Invoking guix package).  Alternatively, specification->package can be used to get the package record from a string without importing its related module.

There are few more essential services, but users are not expected to extend them.

 -- Variable: home-service-type
     The root of home services DAG, it generates a folder, which later will be symlinked to ~/.guix-home, it contains configurations, profile with binaries and libraries, and some necessary scripts to glue things together.

 -- Variable: home-run-on-first-login-service-type
     The service of this type generates a Guile script, which is expected to be executed by the login shell.  It is only executed if the special flag file inside XDG_RUNTIME_DIR hasn't been created, this prevents redundant executions of the script if multiple login shells are spawned.

     It can be extended with a gexp.  However, to autostart an application, users should not use this service, in most cases it's better to extend home-shepherd-service-type with a Shepherd service (see Shepherd Services), or extend the shell's startup file with the required command using the appropriate service type.

 -- Variable: home-files-service-type
     The service of this type allows to specify a list of files, which will go to ~/.guix-home/files, usually this directory contains configuration files (to be more precise it contains symlinks to files in /gnu/store), which should be placed in $XDG_CONFIG_DIR or in rare cases in $HOME.  It accepts extension values in the following format:

          `((".sway/config" ,sway-file-like-object)
            (".tmux.conf" ,(local-file "./tmux.conf")))

     Each nested list contains two values: a subdirectory and file-like object.  After building a home environment ~/.guix-home/files will be populated with appropriate content and all nested directories will be created accordingly, however, those files won't go any further until some other service will do it.  By default a home-symlink-manager-service-type, which creates necessary symlinks in home folder to files from ~/.guix-home/files and backs up already existing, but clashing configs and other things, is a part of essential home services (enabled by default), but it's possible to use alternative services to implement more advanced use cases like read-only home.  Feel free to experiment and share your results.

It is often the case that Guix Home users already have a setup for versioning their user configuration files (also known as dot files) in a single directory, and some way of automatically deploy changes to their user home.

The home-dotfiles-service-type from (gnu home services dotfiles) is designed to ease the way into using Guix Home for this kind of users, allowing them to point the service to their dotfiles directory, which must follow the layout suggested by GNU Stow (https://www.gnu.org/software/stow/), and have their dotfiles automatically deployed to their user home, without migrating them to Guix native configurations.

The dotfiles directory layout is expected to be structured as follows. Please keep in mind that it is advisable to keep your dotfiles directories under version control, for example in the same repository where you'd track your Guix Home configuration.

     ~$ tree -a ./dotfiles/
     dotfiles/
     ├── git
     │   └── .gitconfig
     ├── gpg
     │   └── .gnupg
     │       ├── gpg-agent.conf
     │       └── gpg.conf
     ├── guile
     │   └── .guile
     ├── guix
     │   └── .config
     │       └── guix
     │           └── channels.scm
     ├── nix
     │   ├── .config
     │   │   └── nixpkgs
     │   │       └── config.nix
     │   └── .nix-channels
     ├── tmux
     │   └── .tmux.conf
     └── vim
         └── .vimrc

     13 directories, 10 files

For an informal specification please refer to the Stow manual (see Introduction). A suitable configuration would then be:

     (home-environment
       ;; ...
       (services
         (service home-dotfiles-service-type
                  (home-dotfiles-configuration
                    (directories (list "./dotfiles"))))))

The expected home directory state would then be:

     .
     ├── .config
     │   ├── guix
     │   │   └── channels.scm
     │   └── nixpkgs
     │       └── config.nix
     ├── .gitconfig
     ├── .gnupg
     │   ├── gpg-agent.conf
     │   └── gpg.conf
     ├── .guile
     ├── .nix-channels
     ├── .tmux.conf
     └── .vimrc

 -- Variable: home-dotfiles-service-type
     Return a service which is very similiar to home-files-service-type (and actually extends it), but designed to ease the way into using Guix Home for users that already track their dotfiles under some kind of version control.  This service allows users to point Guix Home to their dotfiles directory and have their files automatically deployed to their home directory just like Stow would, without migrating all of their dotfiles to Guix native configurations.

 -- Data Type: home-dotfiles-configuration
     Available home-dotfiles-configuration fields are:

     source-directory (default: (current-source-directory))
          The path where dotfile directories are resolved. By default dotfile directories are resolved relative the source location where home-dotfiles-configuration appears.

     directories (type: list-of-strings)
          The list of dotfiles directories where home-dotfiles-service-type will look for application dotfiles.

     exclude (default: '(".*~" ".*\\.swp" "\\.git" "\\.gitignore"))
          The list of file patterns home-dotfiles-service-type will exclude while visiting each one of the directories.

 -- Variable: home-xdg-configuration-files-service-type
     The service is very similar to home-files-service-type (and actually extends it), but used for defining files, which will go to ~/.guix-home/files/.config, which will be symlinked to $XDG_CONFIG_DIR by home-symlink-manager-service-type (for example) during activation.  It accepts extension values in the following format:

          `(("sway/config" ,sway-file-like-object)
            ;; -> ~/.guix-home/files/.config/sway/config
            ;; -> $XDG_CONFIG_DIR/sway/config (by symlink-manager)
            ("tmux/tmux.conf" ,(local-file "./tmux.conf")))

 -- Variable: home-activation-service-type
     The service of this type generates a guile script, which runs on every guix home reconfigure invocation or any other action, which leads to the activation of the home environment.

 -- Variable: home-symlink-manager-service-type
     The service of this type generates a guile script, which will be executed during activation of home environment, and do a few following steps:

      1. Reads the content of files/ directory of current and pending home environments.

      2. Cleans up all symlinks created by symlink-manager on previous activation.  Also, sub-directories, which become empty also will be cleaned up.

      3. Creates new symlinks the following way: It looks files/ directory (usually defined with home-files-service-type, home-xdg-configuration-files-service-type and maybe some others), takes the files from files/.config/ subdirectory and put respective links in XDG_CONFIG_DIR.  For example symlink for files/.config/sway/config will end up in $XDG_CONFIG_DIR/sway/config.  The rest files in files/ outside of files/.config/ subdirectory will be treated slightly different: symlink will just go to $HOME. files/.some-program/config will end up in $HOME/.some-program/config.

      4. If some sub-directories are missing, they will be created.

      5. If there is a clashing files on the way, they will be backed up.

     symlink-manager is a part of essential home services and is enabled and used by default.

Shells
------

Shells play a quite important role in the environment initialization process, you can configure them manually as described in section Configuring the Shell, but the recommended way is to use home services listed below.  It's both easier and more reliable.

Each home environment instantiates home-shell-profile-service-type, which creates a ~/.profile startup file for all POSIX-compatible shells.  This file contains all the necessary steps to properly initialize the environment, but many modern shells like Bash or Zsh prefer their own startup files, that's why the respective home services (home-bash-service-type and home-zsh-service-type) ensure that ~/.profile is sourced by ~/.bash_profile and ~/.zprofile, respectively.

Shell Profile Service
.....................

 -- Data Type: home-shell-profile-configuration
     Available home-shell-profile-configuration fields are:

     profile (default: '()) (type: text-config)
          home-shell-profile is instantiated automatically by home-environment, DO NOT create this service manually, it can only be extended.  profile is a list of file-like objects, which will go to ~/.profile.  By default ~/.profile contains the initialization code which must be evaluated by the login shell to make home-environment's profile available to the user, but other commands can be added to the file if it is really necessary.  In most cases shell's configuration files are preferred places for user's customizations. Extend home-shell-profile service only if you really know what you do.

Bash Home Service
.................

 -- Data Type: home-bash-configuration
     Available home-bash-configuration fields are:

     package (default: bash) (type: package)
          The Bash package to use.

     guix-defaults? (default: #t) (type: boolean)
          Add sane defaults like reading /etc/bashrc and coloring the output of ls to the top of the .bashrc file.

     environment-variables (default: '()) (type: alist)
          Association list of environment variables to set for the Bash session.  The rules for the home-environment-variables-service-type apply here (see Essential Home Services).  The contents of this field will be added after the contents of the bash-profile field.

     aliases (default: '()) (type: alist)
          Association list of aliases to set for the Bash session.  The aliases will be defined after the contents of the bashrc field has been put in the .bashrc file.  The alias will automatically be quoted, so something like this:

               '(("ls" . "ls -alF"))

          turns into

               alias ls="ls -alF"

     bash-profile (default: '()) (type: text-config)
          List of file-like objects, which will be added to .bash_profile. Used for executing user's commands at start of login shell (In most cases the shell started on tty just after login).  .bash_login won't be ever read, because .bash_profile always present.

     bashrc (default: '()) (type: text-config)
          List of file-like objects, which will be added to .bashrc.  Used for executing user's commands at start of interactive shell (The shell for interactive usage started by typing bash or by terminal app or any other program).

     bash-logout (default: '()) (type: text-config)
          List of file-like objects, which will be added to .bash_logout. Used for executing user's commands at the exit of login shell.  It won't be read in some cases (if the shell terminates by exec'ing another process for example).

You can extend the Bash service by using the home-bash-extension configuration record, whose fields must mirror that of home-bash-configuration (see home-bash-configuration).  The contents of the extensions will be added to the end of the corresponding Bash configuration files (see Bash Startup Files (The GNU Bash Reference Manual).

For example, here is how you would define a service that extends the Bash service such that ~/.bash_profile defines an additional environment variable, PS1:

     (define bash-fancy-prompt-service
       (simple-service 'bash-fancy-prompt
                       home-bash-service-type
                       (home-bash-extension
                        (environment-variables
                         '(("PS1" . "\\u \\wλ "))))))

You would then add bash-fancy-prompt-service to the list in the services field of your home-environment.  The reference of home-bash-extension follows.

 -- Data Type: home-bash-extension
     Available home-bash-extension fields are:

     environment-variables (default: '()) (type: alist)
          Additional environment variables to set.  These will be combined with the environment variables from other extensions and the base service to form one coherent block of environment variables.

     aliases (default: '()) (type: alist)
          Additional aliases to set.  These will be combined with the aliases from other extensions and the base service.

     bash-profile (default: '()) (type: text-config)
          Additional text blocks to add to .bash_profile, which will be combined with text blocks from other extensions and the base service.

     bashrc (default: '()) (type: text-config)
          Additional text blocks to add to .bashrc, which will be combined with text blocks from other extensions and the base service.

     bash-logout (default: '()) (type: text-config)
          Additional text blocks to add to .bash_logout, which will be combined with text blocks from other extensions and the base service.

Zsh Home Service
................

 -- Data Type: home-zsh-configuration
     Available home-zsh-configuration fields are:

     package (default: zsh) (type: package)
          The Zsh package to use.

     xdg-flavor? (default: #t) (type: boolean)
          Place all the configs to $XDG_CONFIG_HOME/zsh.  Makes ~/.zshenv to set ZDOTDIR to $XDG_CONFIG_HOME/zsh. Shell startup process will continue with $XDG_CONFIG_HOME/zsh/.zshenv.

     environment-variables (default: '()) (type: alist)
          Association list of environment variables to set for the Zsh session.

     zshenv (default: '()) (type: text-config)
          List of file-like objects, which will be added to .zshenv.  Used for setting user's shell environment variables.  Must not contain commands assuming the presence of tty or producing output.  Will be read always.  Will be read before any other file in ZDOTDIR.

     zprofile (default: '()) (type: text-config)
          List of file-like objects, which will be added to .zprofile.  Used for executing user's commands at start of login shell (In most cases the shell started on tty just after login).  Will be read before .zlogin.

     zshrc (default: '()) (type: text-config)
          List of file-like objects, which will be added to .zshrc.  Used for executing user's commands at start of interactive shell (The shell for interactive usage started by typing zsh or by terminal app or any other program).

     zlogin (default: '()) (type: text-config)
          List of file-like objects, which will be added to .zlogin.  Used for executing user's commands at the end of starting process of login shell.

     zlogout (default: '()) (type: text-config)
          List of file-like objects, which will be added to .zlogout.  Used for executing user's commands at the exit of login shell.  It won't be read in some cases (if the shell terminates by exec'ing another process for example).

Inputrc Profile Service
.......................

The GNU Readline package (https://tiswww.cwru.edu/php/chet/readline/rltop.html) includes Emacs and vi editing modes, with the ability to customize the configuration with settings in the ~/.inputrc file.  With the gnu home services shells module, you can setup your readline configuration in a predictable manner, as shown below. For more information about configuring an ~/.inputrc file, see Readline Init File (GNU Readline).

 -- Variable: home-inputrc-service-type

     This is the service to setup various .inputrc configurations. The settings in .inputrc are read by all programs which are linked with GNU Readline.

     Here is an example of a service and its configuration that you could add to the services field of your home-environment:

          (service home-inputrc-service-type
                   (home-inputrc-configuration
                     (key-bindings
                      `(("Control-l" . "clear-screen")))
                     (variables
                      `(("bell-style" . "visible")
                        ("colored-completion-prefix" . #t)
                        ("editing-mode" . "vi")
                        ("show-mode-in-prompt" . #t)))
                     (conditional-constructs
                      `(("$if mode=vi" .
                         ,(home-inputrc-configuration
                            (variables
                             `(("colored-stats" . #t)
                               ("enable-bracketed-paste" . #t)))))
                        ("$else" .
                         ,(home-inputrc-configuration
                            (variables
                             `(("show-all-if-ambiguous" . #t)))))
                        ("endif" . #t)
                        ("$include" . "/etc/inputrc")
                        ("$include" . ,(file-append
                                         (specification->package "readline")
                                         "/etc/inputrc"))))))

     The example above starts with a combination of key-bindings and variables.  The conditional-constructs show how it is possible to add conditionals and includes.  In the example above colored-stats is only enabled if the editing mode is vi style, and it also reads any additional configuration located in /etc/inputrc or in /gnu/store/...-readline/etc/inputrc.

     The value associated with a home-inputrc-service-type instance must be a home-inputrc-configuration record, as described below.

 -- Data Type: home-inputrc-configuration
     Available home-inputrc-configuration fields are:

     key-bindings (default: '()) (type: alist)
          Association list of readline key bindings to be added to the ~/.inputrc file.

               '((\"Control-l\" . \"clear-screen\"))

          turns into

               Control-l: clear-screen

     variables (default: '()) (type: alist)
          Association list of readline variables to set.

               '((\"bell-style\" . \"visible\")
                 (\"colored-completion-prefix\" . #t))

          turns into

               set bell-style visible
               set colored-completion-prefix on

     conditional-constructs (default: '()) (type: alist)
          Association list of conditionals to add to the initialization file.  This includes $if, else, endif and include and they receive a value of another home-inputrc-configuration.

               (conditional-constructs
                `((\"$if mode=vi\" .
                    ,(home-inputrc-configuration
                       (variables
                        `((\"show-mode-in-prompt\" . #t)))))
                  (\"$else\" .
                    ,(home-inputrc-configuration
                       (key-bindings
                        `((\"Control-l\" . \"clear-screen\")))))
                  (\"$endif\" . #t)))

          turns into

               $if mode=vi
               set show-mode-in-prompt on
               $else
               Control-l: clear-screen
               $endif

     extra-content (default: "") (type: text-config)
          Extra content appended as-is to the configuration file.  Run man readline for more information about all the configuration options.

Scheduled User's Job Execution
------------------------------

The (gnu home services mcron) module provides an interface to GNU mcron, a daemon to run jobs at scheduled times (see GNU mcron).  The information about system's mcron is applicable here (see Scheduled Job Execution), the only difference for home services is that they have to be declared in a home-environment record instead of an operating-system record.

 -- Variable: home-mcron-service-type
     This is the type of the mcron home service, whose value is a home-mcron-configuration object.  It allows to manage scheduled tasks.

     This service type can be the target of a service extension that provides additional job specifications (see Service Composition).  In other words, it is possible to define services that provide additional mcron jobs to run.

 -- Data Type: home-mcron-configuration
     Available home-mcron-configuration fields are:

     mcron (default: mcron) (type: file-like)
          The mcron package to use.

     jobs (default: '()) (type: list-of-gexps)
          This is a list of gexps (see G-Expressions), where each gexp corresponds to an mcron job specification (see mcron job specifications (GNU mcron)).

     log? (default: #t) (type: boolean)
          Log messages to standard output.

     log-format (default: "~1@*~a ~a: ~a~%") (type: string)
          (ice-9 format) format string for log messages.  The default value produces messages like "PID NAME: MESSAGE" (see Invoking (GNU mcron)).  Each message is also prefixed by a timestamp by GNU Shepherd.

Power Management Home Services
------------------------------

The (gnu home services pm) module provides home services pertaining to battery power.

 -- Variable: home-batsignal-service-type
     Service for batsignal, a program that monitors battery levels and warns the user through desktop notifications when their battery is getting low.  You can also configure a command to be run when the battery level passes a point deemed ``dangerous''.  This service is configured with the home-batsignal-configuration record.

 -- Data Type: home-batsignal-configuration
     Data type representing the configuration for batsignal.

     warning-level (default: 15)
          The battery level to send a warning message at.

     warning-message (default: #f)
          The message to send as a notification when the battery level reaches the warning-level.  Setting to #f uses the default message.

     critical-level (default: 5)
          The battery level to send a critical message at.

     critical-message (default: #f)
          The message to send as a notification when the battery level reaches the critical-level.  Setting to #f uses the default message.

     danger-level (default: 2)
          The battery level to run the danger-command at.

     danger-command (default: #f)
          The command to run when the battery level reaches the danger-level. Setting to #f disables running the command entirely.

     full-level (default: #f)
          The battery level to send a full message at.  Setting to #f disables sending the full message entirely.

     full-message (default: #f)
          The message to send as a notification when the battery level reaches the full-level.  Setting to #f uses the default message.

     batteries (default: '())
          The batteries to monitor.  Setting to '() tries to find batteries automatically.

     poll-delay (default: 60)
          The time in seconds to wait before checking the batteries again.

     icon (default: #f)
          A file-like object to use as the icon for battery notifications.  Setting to #f disables notification icons entirely.

     notifications? (default: #t)
          Whether to send any notifications.

     notifications-expire? (default: #f)
          Whether notifications sent expire after a time.

     notification-command (default: #f)
          Command to use to send messages.  Setting to #f sends a notification through libnotify.

     ignore-missing? (default: #f)
          Whether to ignore missing battery errors.

Managing User Daemons
---------------------

The (gnu home services shepherd) module supports the definitions of per-user Shepherd services (see Introduction (The GNU Shepherd Manual)).  You extend home-shepherd-service-type with new services; Guix Home then takes care of starting the shepherd daemon for you when you log in, which in turns starts the services you asked for.

 -- Variable: home-shepherd-service-type
     The service type for the userland Shepherd, which allows one to manage long-running processes or one-shot tasks.  User's Shepherd is not an init process (PID 1), but almost all other information described in (see Shepherd Services) is applicable here too.

     This is the service type that extensions target when they want to create shepherd services (see Service Types and Services, for an example). Each extension must pass a list of <shepherd-service>.  Its value must be a home-shepherd-configuration, as described below.

 -- Data Type: home-shepherd-configuration
     This data type represents the Shepherd's configuration.

     shepherd (default: shepherd)
          The Shepherd package to use.

     auto-start? (default: #t)
          Whether or not to start Shepherd on first login.

     services (default: '())
          A list of <shepherd-service> to start. You should probably use the service extension mechanism instead (see Shepherd Services).

Secure Shell
------------

The OpenSSH package (https://www.openssh.com) includes a client, the ssh command, that allows you to connect to remote machines using the SSH (secure shell) protocol.  With the (gnu home services ssh) module, you can set up OpenSSH so that it works in a predictable fashion, almost independently of state on the local machine. To do that, you instantiate home-openssh-service-type in your Home configuration, as explained below.

 -- Variable: home-openssh-service-type
     This is the type of the service to set up the OpenSSH client.  It takes care of several things:

       * providing a ~/.ssh/config file based on your configuration so that ssh knows about hosts you regularly connect to and their associated parameters;

       * providing a ~/.ssh/authorized_keys, which lists public keys that the local SSH server, sshd, may accept to connect to this user account;

       * optionally providing a ~/.ssh/known_hosts file so that ssh can authenticate hosts you connect to.

     Here is an example of a service and its configuration that you could add to the services field of your home-environment:

          (service home-openssh-service-type
                   (home-openssh-configuration
                    (hosts
                     (list (openssh-host (name "ci.guix.gnu.org")
                                         (user "charlie"))
                           (openssh-host (name "chbouib")
                                         (host-name "chbouib.example.org")
                                         (user "supercharlie")
                                         (port 10022))))
                    (authorized-keys (list (local-file "alice.pub")))))

     The example above lists two hosts and their parameters.  For instance, running ssh chbouib will automatically connect to chbouib.example.org on port 10022, logging in as user supercharlie.  Further, it marks the public key in alice.pub as authorized for incoming connections.

     The value associated with a home-openssh-service-type instance must be a home-openssh-configuration record, as describe below.

 -- Data Type: home-openssh-configuration
     This is the datatype representing the OpenSSH client and server configuration in one's home environment.  It contains the following fields:

     hosts (default: '())
          A list of openssh-host records specifying host names and associated connection parameters (see below).  This host list goes into ~/.ssh/config, which ssh reads at startup.

     known-hosts (default: *unspecified*)
          This must be either:

            * *unspecified*, in which case home-openssh-service-type leaves it up to ssh and to the user to maintain the list of known hosts at ~/.ssh/known_hosts, or

            * a list of file-like objects, in which case those are concatenated and emitted as ~/.ssh/known_hosts.

          The ~/.ssh/known_hosts contains a list of host name/host key pairs that allow ssh to authenticate hosts you connect to and to detect possible impersonation attacks.  By default, ssh updates it in a TOFU, trust-on-first-use fashion, meaning that it records the host's key in that file the first time you connect to it. This behavior is preserved when known-hosts is set to *unspecified*.

          If you instead provide a list of host keys upfront in the known-hosts field, your configuration becomes self-contained and stateless: it can be replicated elsewhere or at another point in time. Preparing this list can be relatively tedious though, which is why *unspecified* is kept as a default.

     authorized-keys (default: #false)
          The default #false value means: Leave any ~/.ssh/authorized_keys file alone.  Otherwise, this must be a list of file-like objects, each of which containing an SSH public key that should be authorized to connect to this machine.

          Concretely, these files are concatenated and made available as ~/.ssh/authorized_keys.  If an OpenSSH server, sshd, is running on this machine, then it may take this file into account: this is what sshd does by default, but be aware that it can also be configured to ignore it.

     add-keys-to-agent (default: no)
          This string specifies whether keys should be automatically added to a running ssh-agent.  If this option is set to yes and a key is loaded from a file, the key and its passphrase are added to the agent with the default lifetime, as if by ssh-add.  If this option is set to ask, ssh will require confirmation.  If this option is set to confirm, each use of the key must be confirmed.  If this option is set to no, no keys are added to the agent.  Alternately, this option may be specified as a time interval to specify the key's lifetime in ssh-agent, after which it will automatically be removed.  The argument must be no, yes, confirm (optionally followed by a time interval), ask or a time interval.

 -- Data Type: openssh-host
     Available openssh-host fields are:

     name (type: string)
          Name of this host declaration.  A openssh-host must define only name or match-criteria.  Use host-name \"*\" for top-level options.

     host-name (type: maybe-string)
          Host name---e.g., "foo.example.org" or "192.168.1.2".

     match-criteria (type: maybe-match-criteria)
          When specified, this string denotes the set of hosts to which the entry applies, superseding the host-name field.  Its first element must be all or one of ssh-match-keywords.  The rest of the elements are arguments for the keyword, or other criteria.  A openssh-host must define only name or match-criteria.  Other host configuration options will apply to all hosts matching match-criteria.

     address-family (type: maybe-address-family)
          Address family to use when connecting to this host: one of AF_INET (for IPv4 only), AF_INET6 (for IPv6 only). Additionally, the field can be left unset to allow any address family.

     identity-file (type: maybe-string)
          The identity file to use---e.g., "/home/charlie/.ssh/id_ed25519".

     port (type: maybe-natural-number)
          TCP port number to connect to.

     user (type: maybe-string)
          User name on the remote host.

     forward-x11? (type: maybe-boolean)
          Whether to forward remote client connections to the local X11 graphical display.

     forward-x11-trusted? (type: maybe-boolean)
          Whether remote X11 clients have full access to the original X11 graphical display.

     forward-agent? (type: maybe-boolean)
          Whether the authentication agent (if any) is forwarded to the remote machine.

     compression? (type: maybe-boolean)
          Whether to compress data in transit.

     proxy (type: maybe-proxy-command-or-jump-list)
          The command to use to connect to the server or a list of SSH hosts to jump through before connecting to the server.  The field may be set to either a proxy-command or a list of proxy-jump records.

          As an example, a proxy-command to connect via an HTTP proxy at 192.0.2.0 would be constructed with: (proxy-command "nc -X connect -x 192.0.2.0:8080 %h %p").

           -- Data Type: proxy-jump
               Available proxy-jump fields are:

               user (type: maybe-string)
                    User name on the remote host.

               host-name (type: string)
                    Host name---e.g., foo.example.org or 192.168.1.2.

               port (type: maybe-natural-number)
                    TCP port number to connect to.

     host-key-algorithms (type: maybe-string-list)
          The list of accepted host key algorithms---e.g., '("ssh-ed25519").

     accepted-key-types (type: maybe-string-list)
          The list of accepted user public key types.

     extra-content (default: "") (type: raw-configuration-string)
          Extra content appended as-is to this Host block in ~/.ssh/config.

The parcimonie service runs a daemon that slowly refreshes a GnuPG public key from a keyserver.  It refreshes one key at a time; between every key update parcimonie sleeps a random amount of time, long enough for the previously used Tor circuit to expire.  This process is meant to make it hard for an attacker to correlate the multiple key update.

As an example, here is how you would configure parcimonie to refresh the keys in your GnuPG keyring, as well as those keyrings created by Guix, such as when running guix import:

     (service home-parcimonie-service-type
              (home-parcimonie-configuration
                (refresh-guix-keyrings? #t)))

This assumes that the Tor anonymous routing daemon is already running on your system.  On Guix System, this can be achieved by setting up tor-service-type (see tor-service-type).

The service reference is given below.

 -- Variable: parcimonie-service-type
     This is the service type for parcimonie (Parcimonie's web site (https://salsa.debian.org/intrigeri/parcimonie)). Its value must be a home-parcimonie-configuration, as shown below.

 -- Data Table: home-parcimonie-configuration
     Available home-parcimonie-configuration fields are:

     parcimonie (default: parcimonie) (type: file-like)
          The parcimonie package to use.

     verbose? (default: #f) (type: boolean)
          Whether to have more verbose logging from the service.

     gnupg-already-torified? (default: #f) (type: boolean)
          Whether GnuPG is already configured to pass all traffic through Tor (https://torproject.org).

     refresh-guix-keyrings? (default: #f) (type: boolean)
          Guix creates a few keyrings in the $XDG_CONFIG_DIR, such as when running guix import (see Invoking guix import).  Setting this to #t will also refresh any keyrings which Guix has created.

     extra-content (default: #f) (type: raw-configuration-string)
          Raw content to add to the parcimonie command.

The OpenSSH package (https://www.openssh.com) includes a daemon, the ssh-agent command, that manages keys to connect to remote machines using the SSH (secure shell) protocol.  With the (gnu home services ssh) service, you can configure the OpenSSH ssh-agent to run upon login.  See home-gpg-agent-service-type, for an alternative to OpenSSH's ssh-agent.

Here is an example of a service and its configuration that you could add to the services field of your home-environment:

     (service home-ssh-agent-service-type
              (home-ssh-agent-configuration
               (extra-options '("-t" "1h30m"))))

 -- Variable: home-ssh-agent-service-type
     This is the type of the ssh-agent home service, whose value is a home-ssh-agent-configuration object.

 -- Data Type: home-ssh-agent-configuration
     Available home-ssh-agent-configuration fields are:

     openssh (default: openssh) (type: file-like)
          The OpenSSH package to use.

     socket-directory (default: XDG_RUNTIME_DIR/ssh-agent") (type: gexp)
          The directory to write the ssh-agent's socket file.

     extra-options (default: '())
          Extra options will be passed to ssh-agent, please run man ssh-agent for more information.

GNU Privacy Guard
-----------------

The (gnu home services gnupg) module provides services that help you set up the GNU Privacy Guard, also known as GnuPG or GPG, in your home environment.

The gpg-agent service configures and sets up GPG's agent, the program that is responsible for managing OpenPGP private keys and, optionally, OpenSSH (secure shell) private keys (see Invoking GPG-AGENT (Using the GNU Privacy Guard)).

As an example, here is how you would configure gpg-agent with SSH support such that it uses the Emacs-based Pinentry interface when prompting for a passphrase:

     (service home-gpg-agent-service-type
              (home-gpg-agent-configuration
               (pinentry-program
                (file-append pinentry-emacs "/bin/pinentry-emacs"))
               (ssh-support? #t)))

The service reference is given below.

 -- Variable: home-gpg-agent-service-type
     This is the service type for gpg-agent (see Invoking GPG-AGENT (Using the GNU Privacy Guard)).  Its value must be a home-gpg-agent-configuration, as shown below.

 -- Data Type: home-gpg-agent-configuration
     Available home-gpg-agent-configuration fields are:

     gnupg (default: gnupg) (type: file-like)
          The GnuPG package to use.

     pinentry-program (type: file-like)
          Pinentry program to use.  Pinentry is a small user interface that gpg-agent delegates to anytime it needs user input for a passphrase or PIN (personal identification number) (see Using the PIN-Entry).

     ssh-support? (default: #f) (type: boolean)
          Whether to enable SSH (secure shell) support.  When true, gpg-agent acts as a drop-in replacement for OpenSSH's ssh-agent program, taking care of OpenSSH secret keys and directing passphrase requests to the chosen Pinentry program.

     default-cache-ttl (default: 600) (type: integer)
          Time a cache entry is valid, in seconds.

     max-cache-ttl (default: 7200) (type: integer)
          Maximum time a cache entry is valid, in seconds.  After this time a cache entry will be expired even if it has been accessed recently.

     default-cache-ttl-ssh (default: 1800) (type: integer)
          Time a cache entry for SSH keys is valid, in seconds.

     max-cache-ttl-ssh (default: 7200) (type: integer)
          Maximum time a cache entry for SSH keys is valid, in seconds.

     extra-content (default: "") (type: raw-configuration-string)
          Raw content to add to the end of ~/.gnupg/gpg-agent.conf.

Desktop Home Services
---------------------

The (gnu home services desktop) module provides services that you may find useful on ``desktop'' systems running a graphical user environment such as Xorg.

 -- Variable: home-x11-service-type
     This is the service type representing the X Window graphical display server (also referred to as ``X11'').

     X Window is necessarily started by a system service; on Guix System, starting it is the responsibility of gdm-service-type and similar services (see X Window).  At the level of Guix Home, as an unprivileged user, we cannot start X Window; all we can do is check whether it is running.  This is what this service does.

     As a user, you probably don't need to worry or explicitly instantiate home-x11-service-type.  Services that require an X Window graphical display, such as home-redshift-service-type below, instantiate it and depend on its corresponding x11-display Shepherd service (see Shepherd Home Service).

     When X Window is running, the x11-display Shepherd service starts and sets the DISPLAY environment variable of the shepherd process, using its original value if it was already set; otherwise, it fails to start.

     The service can also be forced to use a given value for DISPLAY, like so:

          herd start x11-display :3

     In the example above, x11-display is instructed to set DISPLAY to :3.

 -- Variable: home-redshift-service-type
     This is the service type for Redshift (https://github.com/jonls/redshift), a program that adjusts the display color temperature according to the time of day.  Its associated value must be a home-redshift-configuration record, as shown below.

     A typical configuration, where we manually specify the latitude and longitude, might look like this:

          (service home-redshift-service-type
                   (home-redshift-configuration
                    (location-provider 'manual)
                    (latitude 35.81)    ;northern hemisphere
                    (longitude -0.80))) ;west of Greenwich

 -- Data Type: home-redshift-configuration
     Available home-redshift-configuration fields are:

     redshift (default: redshift) (type: file-like)
          Redshift package to use.

     location-provider (default: geoclue2) (type: symbol)
          Geolocation provider---'manual or 'geoclue2.  In the former case, you must also specify the latitude and longitude fields so Redshift can determine daytime at your place. In the latter case, the Geoclue system service must be running; it will be queried for location information.

     adjustment-method (default: randr) (type: symbol)
          Color adjustment method.

     daytime-temperature (default: 6500) (type: integer)
          Daytime color temperature (kelvins).

     nighttime-temperature (default: 4500) (type: integer)
          Nighttime color temperature (kelvins).

     daytime-brightness (type: maybe-inexact-number)
          Daytime screen brightness, between 0.1 and 1.0, or left unspecified.

     nighttime-brightness (type: maybe-inexact-number)
          Nighttime screen brightness, between 0.1 and 1.0, or left unspecified.

     latitude (type: maybe-inexact-number)
          Latitude, when location-provider is 'manual.

     longitude (type: maybe-inexact-number)
          Longitude, when location-provider is 'manual.

     dawn-time (type: maybe-string)
          Custom time for the transition from night to day in the morning---"HH:MM" format.  When specified, solar elevation is not used to determine the daytime/nighttime period.

     dusk-time (type: maybe-string)
          Likewise, custom time for the transition from day to night in the evening.

     extra-content (default: "") (type: raw-configuration-string)
          Extra content appended as-is to the Redshift configuration file.  Run man redshift for more information about the configuration file format.

 -- Variable: home-dbus-service-type
     This is the service type for running a session-specific D-Bus, for unprivileged applications that require D-Bus to be running.

 -- Data Type: home-dbus-configuration
     The configuration record for home-dbus-service-type.

     dbus (default: dbus)
          The package providing the /bin/dbus-daemon command.

 -- Variable: home-unclutter-service-type
     This is the service type for Unclutter, a program that runs on the background of an X11 session and detects when the X pointer hasn't moved for a specified idle timeout, after which it hides the cursor so that you can focus on the text underneath.  Its associated value must be a home-unclutter-configuration record, as shown below.

     A typical configuration, where we manually specify the idle timeout (in seconds), might look like this:

          (service home-unclutter-service-type
                   (home-unclutter-configuration
                    (idle-timeout 2)))

 -- Data Type: home-unclutter-configuration
     The configuration record for home-unclutter-service-type.

     unclutter (default: unclutter) (type: file-like)
          Unclutter package to use.

     idle-timeout (default: 5) (type: integer)
          A timeout in seconds after which to hide cursor.

 -- Variable: home-xmodmap-service-type
     This is the service type for the xmodmap (https://gitlab.freedesktop.org/xorg/app/xmodmap) utility to modify keymaps and pointer button mappings under the Xorg display server.  Its associated value must be a home-xmodmap-configuration record, as shown below.

     The key-map field takes a list of objects, each of which is either a statement (a string) or an assignment (a pair of strings).  As an example, the snippet below swaps around the Caps_Lock and the Control_L keys, by first removing the keysyms (on the right-hand side) from the corresponding modifier maps (on the left-hand side), re-assigning them by swapping each other out, and finally adding back the keysyms to the modifier maps.

          (service home-xmodmap-service-type
                   (home-xmodmap-configuration
                    (key-map '(("remove Lock" . "Caps_Lock")
                               ("remove Control" . "Control_L")
                               ("keysym Control_L" . "Caps_Lock")
                               ("keysym Caps_Lock" . "Control_L")
                               ("add Lock" . "Caps_Lock")
                               ("add Control" . "Control_L")))))

 -- Data Type: home-xmodmap-configuration
     The configuration record for home-xmodmap-service-type.  Its available fields are:

     xmodmap (default: xmodmap) (type: file-like)
          The xmodmap package to use.

     key-map (default: '()) (type: list)
          The list of expressions to be read by xmodmap on service startup.

Guix Home Services
------------------

The (gnu home services guix) module provides services for user-specific Guix configuration.

 -- Variable: home-channels-service-type
     This is the service type for managing $XDG_CONFIG_HOME/guix/channels.scm, the file that controls the channels received on guix pull (see Channels).  Its associated value is a list of channel records, defined in the (guix channels) module.

     Generally, it is better to extend this service than to directly configure it, as its default value is the default guix channel(s) defined by %default-channels.  If you configure this service directly, be sure to include a guix channel.  See Specifying Additional Channels and Using a Custom Guix Channel for more details.

     A typical extension for adding a channel might look like this:

          (simple-service 'variant-packages-service
                          home-channels-service-type
                          (list
                           (channel
                            (name 'variant-packages)
                            (url "https://example.org/variant-packages.git"))))

Fonts Home Services
-------------------

The (gnu home services fontutils) module provides services for user-specific Fontconfig setup.  The Fontconfig (https://www.freedesktop.org/wiki/Software/fontconfig) library is used by many applications to access fonts on the system.

 -- Variable: home-fontconfig-service-type
     This is the service type for generating configurations for Fontconfig. Its associated value is a list of either strings (or gexps) pointing to fonts locations, or SXML (see SXML (GNU Guile Reference Manual)) fragments to be converted into XML and put inside the main fontconfig node.

     Generally, it is better to extend this service than to directly configure it, as its default value is the default Guix Home's profile font installation path (~/.guix-home/profile/share/fonts).  If you configure this service directly, be sure to include the above directory.

     Here's how you'd extend it to include fonts installed with the Nix package manager, and to prefer your favourite monospace font:

          (simple-service 'additional-fonts-service
                          home-fontconfig-service-type
                          (list "~/.nix-profile/share/fonts"
                                '(alias
                                  (family "monospace")
                                  (prefer
                                   (family "Liberation Mono")))))

Sound Home Services
-------------------

The (gnu home services sound) module provides services related to sound support.

PulseAudio RTP Streaming Services
.................................

The following services dynamically reconfigure the PulseAudio sound server (https://pulseaudio.org): they let you toggle broadcast of audio output over the network using the RTP (real-time transport protocol) and, correspondingly, playback of sound received over RTP.  Once home-pulseaudio-rtp-sink-service-type is among your home services, you can start broadcasting audio output by running this command:

     herd start pulseaudio-rtp-sink

You can then run a PulseAudio-capable mixer, such as pavucontrol or pulsemixer (both from the same-named package) to control which audio stream(s) should be sent to the RTP ``sink''.

By default, audio is broadcasted to a multicast address: any device on the LAN (local area network) receives it and may play it. Using multicast in this way puts a lot of pressure on the network and degrades its performance, so you may instead prefer sending to specifically one device.  The first way to do that is by specifying the IP address of the target device when starting the service:

     herd start pulseaudio-rtp-sink 192.168.1.42

The other option is to specify this IP address as the one to use by default in your home environment configuration:

     (service home-pulseaudio-rtp-sink-service-type
              "192.168.1.42")

On the device where you intend to receive and play the RTP stream, you can use home-pulseaudio-rtp-source-service-type, like so:

     (service home-pulseaudio-rtp-source-service-type)

This will then let you start the receiving module for PulseAudio:

     herd start pulseaudio-rtp-source

Again, by default it will listen on the multicast address.  If, instead, you'd like it to listen for direct incoming connections, you can do that by running:

     (service home-pulseaudio-rtp-source-service-type
              "0.0.0.0")

The reference of these services is given below.

 -- Variable: home-pulseaudio-rtp-sink-service-type
 -- Variable: home-pulseaudio-rtp-source-service-type
     This is the type of the service to send, respectively receive, audio streams over RTP (real-time transport protocol).

     The value associated with this service is the IP address (a string) where to send, respectively receive, the audio stream.  By default, audio is sent/received on multicast address %pulseaudio-rtp-multicast-address.

     This service defines one Shepherd service: pulseaudio-rtp-sink, respectively pulseaudio-rtp-source.  The service is not started by default, so you have to explicitly start it when you want to turn it on, as in this example:

          herd start pulseaudio-rtp-sink

     Stopping the Shepherd service turns off broadcasting.

 -- Variable: %pulseaudio-rtp-multicast-address
     This is the multicast address used by default by the two services above.

PipeWire Home Service
.....................

PipeWire (https://pipewire.org) provides a low-latency, graph-based audio and video processing service.  In addition to its native protocol, it can also be used as a replacement for both JACK and PulseAudio.

While PipeWire provides the media processing and API, it does not, directly, know about devices such as sound cards, nor how you might want to connect applications, hardware, and media processing filters. Instead, PipeWire relies on a session manager to specify all these relationships.  While you may use any session manager you wish, for most people the WirePlumber (https://pipewire.pages.freedesktop.org/wireplumber/) session manager, a reference implementation provided by the PipeWire project itself, suffices, and that is the one home-pipewire-service-type uses.

PipeWire can be used as a replacement for PulseAudio by setting enable-pulseaudio? to #t in home-pipewire-configuration, so that existing PulseAudio clients may use it without any further configuration.

In addition, JACK clients may connect to PipeWire by using the pw-jack program, which comes with PipeWire.  Simply prefix the command with pw-jack when you run it, and audio data should go through PipeWire:

     pw-jack mpv -ao=jack sound-file.wav

For more information on PulseAudio emulation, see https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/Config-PulseAudio, for JACK, see https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/Config-JACK.

As PipeWire does not use dbus to start its services on demand (as PulseAudio does), home-pipewire-service-type uses Shepherd to start services when logged in, provisioning the pipewire, wireplumber, and, if configured, pipewire-pulseaudio services.  See Shepherd Home Service.

 -- Variable: home-pipewire-service-type
     This provides the service definition for pipewire, which will run on login.  Its value is a home-pipewire-configuration object.

     To start the service, add it to the service field of your home-environment, such as:

          (service home-pipewire-service-type)

 -- Data Type: home-pipewire-configuration
     Available home-pipewire-configuration fields are:

     pipewire (default: pipewire) (type: file-like)
          The PipeWire package to use.

     wireplumber (default: wireplumber) (type: file-like)
          The WirePlumber package to use.

     enable-pulseaudio? (default: #t) (type: boolean)
          When true, enable PipeWire's PulseAudio emulation support, allowing PulseAudio clients to use PipeWire transparently.

Mail Home Services
------------------

The (gnu home services mail) module provides services that help you set up the tools to work with emails in your home environment.

MSMTP (https://marlam.de/msmtp) is a SMTP (Simple Mail Transfer Protocol) client.  It sends mail to a predefined SMTP server that takes care of proper delivery.

The service reference is given below.

 -- Variable: home-msmtp-service-type
     This is the service type for msmtp.  Its value must be a home-msmtp-configuration, as shown below.  It provides the ~/.config/msmtp/config file.

     As an example, here is how you would configure msmtp for a single account:

          (service home-msmtp-service-type
                   (home-msmtp-configuration
                    (accounts
                     (list
                      (msmtp-account
                       (name "alice")
                       (configuration
                        (msmtp-configuration
                         (host "mail.example.org")
                         (port 587)
                         (user "alice")
                         (password-eval "pass Mail/alice"))))))))

 -- Data Type: home-msmtp-configuration
     Available home-msmtp-configuration fields are:

     defaults (type: msmtp-configuration)
          The configuration that will be set as default for all accounts.

     accounts (default: '()) (type: list-of-msmtp-accounts)
          A list of msmtp-account records which contain information about all your accounts.

     default-account (type: maybe-string)
          Set the default account.

     extra-content (default: "") (type: string)
          Extra content appended as-is to the configuration file.  Run man msmtp for more information about the configuration file format.

 -- Data Type: msmtp-account
     Available msmtp-account fields are:

     name (type: string)
          The unique name of the account.

     configuration (type: msmtp-configuration)
          The configuration for this given account.

 -- Data Type: msmtp-configuration
     Available msmtp-configuration fields are:

     auth? (type: maybe-boolean)
          Enable or disable authentication.

     tls? (type: maybe-boolean)
          Enable or disable TLS (also known as SSL) for secured connections.

     tls-starttls? (type: maybe-boolean)
          Choose the TLS variant: start TLS from within the session (‘on’, default), or tunnel the session through TLS (‘off’).

     tls-trust-file (type: maybe-string)
          Activate server certificate verification using a list of trusted Certification Authorities (CAs).

     log-file (type: maybe-string)
          Enable logging to the specified file.  An empty argument disables logging.  The file name ‘-’ directs the log information to standard output.

     host (type: maybe-string)
          The SMTP server to send the mail to.

     port (type: maybe-integer)
          The port that the SMTP server listens on.  The default is 25 ("smtp"), unless TLS without STARTTLS is used, in which case it is 465 ("smtps").

     user (type: maybe-string)
          Set the user name for authentication.

     from (type: maybe-string)
          Set the envelope-from address.

     password-eval (type: maybe-string)
          Set the password for authentication to the output (stdout) of the command cmd.

     extra-content (default: "") (type: string)
          Extra content appended as-is to the configuration block.  Run man msmtp for more information about the configuration file format.

Messaging Home Services
-----------------------

The ZNC bouncer (https://znc.in) can be run as a daemon to manage your IRC presence.  With the (gnu home services messaging) service, you can configure ZNC to run upon login.

You will have to provide a ~/.znc/configs/znc.conf separately.

Here is an example of a service and its configuration that you could add to the services field of your home-environment:

     (service home-znc-service-type)

 -- Variable: home-znc-service-type
     This is the type of the ZNC home service, whose value is a home-znc-configuration object.

 -- Data Type: home-znc-configuration
     Available home-znc-configuration fields are:

     znc (default: znc) (type: file-like)
          The ZNC package to use.

     extra-options (default: '())
          Extra options will be passed to znc, please run man znc for more information.

Media Home Services
-------------------

The Kodi media center (https://kodi.tv) can be run as a daemon on a media server.  With the (gnu home services kodi) service, you can configure Kodi to run upon login.

Here is an example of a service and its configuration that you could add to the services field of your home-environment:

     (service home-kodi-service-type
       (home-kodi-configuration
        (extra-options '("--settings="<settings-file>"))))

 -- Variable: home-kodi-service-type
     This is the type of the Kodi home service, whose value is a home-kodi-configuration object.

 -- Data Type: home-kodi-configuration
     Available home-kodi-configuration fields are:

     kodi (default: kodi) (type: file-like)
          The Kodi package to use.

     extra-options (default: '())
          Extra options will be passed to kodi, please run man kodi for more information.

Networking Home Services
------------------------

This section lists services somewhat networking-related that you may use with Guix Home.

The (gnu home services syncthing) module provides a service to set up the https://syncthing.net (Syncthing) continuous file backup service.

 -- Variable: home-syncthing-service-type
     This is the service type for the syncthing daemon; it is the Home counterpart of the syncthing-service-type system service (see syncthing-service-type).  The value for this service type is a syncthing-configuration.

     Here is how you would set it up with the default configuration:

          (service home-syncthing-service-type)

     For a custom configuration, wrap you syncthing-configuration in for-home, as in this example:

          (service home-syncthing-service-type
                   (for-home
                    (syncthing-configuration (logflags 5))))

     For details about syncthing-configuration, check out the documentation of the system service (see syncthing-service-type).

Miscellaneous Home Services
---------------------------

This section lists Home services that lack a better place.

Dictionary Service
..................

The (gnu home services dict) module provides the following service:

 -- Variable: home-dicod-service-type
     This is the type of the service that runs the dicod daemon, an implementation of DICT server (see Dicod (GNU Dico Manual)).

     You can add open localhost to your ~/.dico file to make localhost the default server for dico client (see Initialization File (GNU Dico Manual)).

This service is a direct mapping of the dicod-service-type system service (see Dictionary Service).  You can use it like this:

     (service home-dicod-service-type)

You may specify a custom configuration by providing a dicod-configuration record, exactly like for dicod-service-type, but wrapping it in for-home:

     (service home-dicod-service-type
              (for-home
               (dicod-configuration ...)))

Invoking guix home
==================

Once you have written a home environment declaration (see Declaring the Home Environment, it can be instantiated using the guix home command.  The synopsis is:

     guix home OPTIONS... ACTION FILE

FILE must be the name of a file containing a home-environment declaration.  ACTION specifies how the home environment is instantiated, but there are few auxiliary actions which don't instantiate it.  Currently the following values are supported:

search
     Display available home service type definitions that match the given regular expressions, sorted by relevance:

          $ guix home search shell
          name: home-shell-profile
          location: gnu/home/services/shells.scm:100:2
          extends: home-files
          description: Create `~/.profile', which is used for environment initialization of POSIX compliant login shells.
          + This service type can be extended with a list of file-like objects.
          relevance: 6

          name: home-fish
          location: gnu/home/services/shells.scm:640:2
          extends: home-files home-profile
          description: Install and configure Fish, the friendly interactive shell.
          relevance: 3

          name: home-zsh
          location: gnu/home/services/shells.scm:290:2
          extends: home-files home-profile
          description: Install and configure Zsh.
          relevance: 1

          name: home-bash
          location: gnu/home/services/shells.scm:508:2
          extends: home-files home-profile
          description: Install and configure GNU Bash.
          relevance: 1

          ...

     As for guix search, the result is written in recutils format, which makes it easy to filter the output (see GNU recutils databases (GNU recutils manual)).

container
     Spawn a shell in an isolated environment---a container---containing your home as specified by FILE.

     For example, this is how you would start an interactive shell in a container with your home:

          guix home container config.scm

     This is a throw-away container where you can lightheartedly fiddle with files; any changes made within the container, any process started---all this disappears as soon as you exit that shell.

     As with guix shell, several options control that container:

     --network
     -N
          Enable networking within the container (it is disabled by default).

     --expose=SOURCE[=TARGET]
     --share=SOURCE[=TARGET]
          As with guix shell, make directory SOURCE of the host system available as TARGET inside the container---read-only if you pass --expose, and writable if you pass --share (see --expose and --share).

     Additionally, you can run a command in that container, instead of spawning an interactive shell.  For instance, here is how you would check which Shepherd services are started in a throw-away home container:

          guix home container config.scm -- herd status

     The command to run in the container must come after -- (double hyphen).

edit
     Edit or view the definition of the given Home service types.

     For example, the command below opens your editor, as specified by the EDITOR environment variable, on the definition of the home-mcron service type:

          guix home edit home-mcron

reconfigure
     Build the home environment described in FILE, and switch to it. Switching means that the activation script will be evaluated and (in basic scenario) symlinks to configuration files generated from home-environment declaration will be created in ~.  If the file with the same path already exists in home folder it will be moved to ~/TIMESTAMP-guix-home-legacy-configs-backup, where TIMESTAMP is a current UNIX epoch time.

          It is highly recommended to run guix pull once before you run guix home reconfigure for the first time (see Invoking guix pull).

     This effects all the configuration specified in FILE.  The command starts Shepherd services specified in FILE that are not currently running; if a service is currently running, this command will arrange for it to be upgraded the next time it is stopped (e.g. by herd stop SERVICE or herd restart SERVICE).

     This command creates a new generation whose number is one greater than the current generation (as reported by guix home list-generations).  If that generation already exists, it will be overwritten.  This behavior mirrors that of guix package (see Invoking guix package).

     Upon completion, the new home is deployed under ~/.guix-home. This directory contains provenance meta-data: the list of channels in use (see Channels) and FILE itself, when available.  You can view the provenance information by running:

          guix home describe

     This information is useful should you later want to inspect how this particular generation was built.  In fact, assuming FILE is self-contained, you can later rebuild generation N of your home environment with:

          guix time-machine \
            -C /var/guix/profiles/per-user/USER/guix-home-N-link/channels.scm -- \
            home reconfigure \
            /var/guix/profiles/per-user/USER/guix-home-N-link/configuration.scm

     You can think of it as some sort of built-in version control!  Your home is not just a binary artifact: it carries its own source.

switch-generation
     Switch to an existing home generation.  This action atomically switches the home profile to the specified home generation.

     The target generation can be specified explicitly by its generation number.  For example, the following invocation would switch to home generation 7:

          guix home switch-generation 7

     The target generation can also be specified relative to the current generation with the form +N or -N, where +3 means ``3 generations ahead of the current generation,'' and -1 means ``1 generation prior to the current generation.''  When specifying a negative value such as -1, you must precede it with -- to prevent it from being parsed as an option.  For example:

          guix home switch-generation -- -1

     This action will fail if the specified generation does not exist.

roll-back
     Switch to the preceding home generation.  This is the inverse of reconfigure, and it is exactly the same as invoking switch-generation with an argument of -1.

delete-generations
     Delete home generations, making them candidates for garbage collection (see Invoking guix gc, for information on how to run the ``garbage collector'').

     This works in the same way as guix package --delete-generations (see --delete-generations).  With no arguments, all home generations but the current one are deleted:

          guix home delete-generations

     You can also select the generations you want to delete.  The example below deletes all the home generations that are more than two months old:

          guix home delete-generations 2m

build
     Build the derivation of the home environment, which includes all the configuration files and programs needed.  This action does not actually install anything.

describe
     Describe the current home generation: its file name, as well as provenance information when available.

     To show installed packages in the current home generation's profile, the --list-installed flag is provided, with the same syntax that is used in guix package --list-installed (see Invoking guix package).  For instance, the following command shows a table of all the packages with ``emacs'' in their name that are installed in the current home generation's profile:

          guix home describe --list-installed=emacs

list-generations
     List a summary of each generation of the home environment available on disk, in a human-readable way.  This is similar to the --list-generations option of guix package (see Invoking guix package).

     Optionally, one can specify a pattern, with the same syntax that is used in guix package --list-generations, to restrict the list of generations displayed.  For instance, the following command displays generations that are up to 10 days old:

          guix home list-generations 10d

     The --list-installed flag may also be specified, with the same syntax that is used in guix home describe.  This may be helpful if trying to determine when a package was added to the home profile.

import
     Generate a home environment from the packages in the default profile and configuration files found in the user's home directory.  The configuration files will be copied to the specified directory, and a home-configuration.scm will be populated with the home environment.  Note that not every home service that exists is supported (see Home Services).

          $ guix home import ~/guix-config
          guix home: '/home/alice/guix-config' populated with all the Home configuration files

And there's more!  guix home also provides the following sub-commands to visualize how the services of your home environment relate to one another:

extension-graph
     Emit to standard output the service extension graph of the home environment defined in FILE (see Service Composition, for more information on service extensions).  By default the output is in Dot/Graphviz format, but you can choose a different format with --graph-backend, as with guix graph (see --backend):

     The command:

          guix home extension-graph FILE | xdot -

     shows the extension relations among services.

shepherd-graph
     Emit to standard output the dependency graph of shepherd services of the home environment defined in FILE.  See Shepherd Services, for more information and for an example graph.

     Again, the default output format is Dot/Graphviz, but you can pass --graph-backend to select a different one.

OPTIONS can contain any of the common build options (see Common Build Options).  In addition, OPTIONS can contain one of the following:

--expression=EXPR
-e EXPR
     Consider the home-environment EXPR evaluates to. This is an alternative to specifying a file which evaluates to a home environment.

--allow-downgrades
     Instruct guix home reconfigure to allow system downgrades.

     Just like guix system, guix home reconfigure, by default, prevents you from downgrading your home to older or unrelated revisions compared to the channel revisions that were used to deploy it---those shown by guix home describe.  Using --allow-downgrades allows you to bypass that check, at the risk of downgrading your home---be careful!

Documentation
*************

In most cases packages installed with Guix come with documentation. There are two main documentation formats: ``Info'', a browsable hypertext format used for GNU software, and ``manual pages'' (or ``man pages''), the linear documentation format traditionally found on Unix. Info manuals are accessed with the info command or with Emacs, and man pages are accessed using man.

You can look for documentation of software installed on your system by keyword.  For example, the following command searches for information about ``TLS'' in Info manuals:

     $ info -k TLS
     "(emacs)Network Security" -- STARTTLS
     "(emacs)Network Security" -- TLS
     "(gnutls)Core TLS API" -- gnutls_certificate_set_verify_flags
     "(gnutls)Core TLS API" -- gnutls_certificate_set_verify_function
     ...

The command below searches for the same keyword in man pages (The database searched by man -k is only created in profiles that contain the man-db package.):

     $ man -k TLS
     SSL (7)              - OpenSSL SSL/TLS library
     certtool (1)         - GnuTLS certificate tool
     ...{}

These searches are purely local to your computer so you have the guarantee that documentation you find corresponds to what you have actually installed, you can access it off-line, and your privacy is respected.

Once you have these results, you can view the relevant documentation by running, say:

     $ info "(gnutls)Core TLS API"

or:

     $ man certtool

Info manuals contain sections and indices as well as hyperlinks like those found in Web pages.  The info reader (see Info reader (Stand-alone GNU Info)) and its Emacs counterpart (see Misc Help (The GNU Emacs Manual)) provide intuitive key bindings to navigate manuals.  See Getting Started (Info: An Introduction), for an introduction to Info navigation.

Platforms
*********

The packages and systems built by Guix are intended, like most computer programs, to run on a CPU with a specific instruction set, and under a specific operating system.  Those programs are often also targeting a specific kernel and system library.  Those constraints are captured by Guix in platform records.

platform Reference
==================

The platform data type describes a platform: an ISA (instruction set architecture), combined with an operating system and possibly additional system-wide settings such as the ABI (application binary interface).

 -- Data Type: platform
     This is the data type representing a platform.

     target
          This field specifies the platform's GNU triplet as a string (see GNU configuration triplets (Autoconf)).

     system
          This string is the system type as it is known to Guix and passed, for instance, to the --system option of most commands.

          It usually has the form "CPU-KERNEL", where CPU is the target CPU and KERNEL the target operating system kernel.

          It can be for instance "aarch64-linux" or "armhf-linux". You will encounter system types when you perform native builds (see Native Builds).

     linux-architecture (default: #false)
          This optional string field is only relevant if the kernel is Linux.  In that case, it corresponds to the ARCH variable used when building Linux, "mips" for instance.

     rust-target (default: #false)
          This optional string field is used to determine which rust target is best supported by this platform.  For example, the base level system targeted by armhf-linux system is closest to armv7-unknown-linux-gnueabihf.

     glibc-dynamic-linker
          This field is the name of the GNU C Library dynamic linker for the corresponding system, as a string.  It can be "/lib/ld-linux-armhf.so.3".

Supported Platforms
===================

The (guix platforms ...) modules export the following variables, each of which is bound to a platform record.

 -- Variable: armv7-linux
     Platform targeting ARM v7 CPU running GNU/Linux.

 -- Variable: aarch64-linux
     Platform targeting ARM v8 CPU running GNU/Linux.

 -- Variable: mips64-linux
     Platform targeting MIPS little-endian 64-bit CPU running GNU/Linux.

 -- Variable: powerpc-linux
     Platform targeting PowerPC big-endian 32-bit CPU running GNU/Linux.

 -- Variable: powerpc64le-linux
     Platform targeting PowerPC little-endian 64-bit CPU running GNU/Linux.

 -- Variable: riscv64-linux
     Platform targeting RISC-V 64-bit CPU running GNU/Linux.

 -- Variable: i686-linux
     Platform targeting x86 CPU running GNU/Linux.

 -- Variable: x86_64-linux
     Platform targeting x86 64-bit CPU running GNU/Linux.

 -- Variable: i686-mingw
     Platform targeting x86 CPU running Windows, with run-time support from MinGW.

 -- Variable: x86_64-mingw
     Platform targeting x86 64-bit CPU running Windows, with run-time support from MinGW.

 -- Variable: i586-gnu
     Platform targeting x86 CPU running GNU/Hurd (also referred to as ``GNU'').

 -- Variable: avr
     Platform targeting AVR CPUs without an operating system, with run-time support from AVR Libc.

 -- Variable: or1k-elf
     Platform targeting OpenRISC 1000 CPU without an operating system and without a C standard library.

Creating System Images
**********************

When it comes to installing Guix System for the first time on a new machine, you can basically proceed in three different ways.  The first one is to use an existing operating system on the machine to run the guix system init command (see Invoking guix system).  The second one, is to produce an installation image (see Building the Installation Image). This is a bootable system which role is to eventually run guix system init.  Finally, the third option would be to produce an image that is a direct instantiation of the system you wish to run.  That image can then be copied on a bootable device such as an USB drive or a memory card.  The target machine would then directly boot from it, without any kind of installation procedure.

The guix system image command is able to turn an operating system definition into a bootable image.  This command supports different image types, such as mbr-hybrid-raw, iso9660 and docker.  Any modern x86_64 machine will probably be able to boot from an iso9660 image.  However, there are a few machines out there that require specific image types.  Those machines, in general using ARM processors, may expect specific partitions at specific offsets.

This chapter explains how to define customized system images and how to turn them into actual bootable images.

image Reference
===============

The image record, described right after, allows you to define a customized bootable system image.

 -- Data Type: image
     This is the data type representing a system image.

     name (default: #false)
          The image name as a symbol, 'my-iso9660 for instance.  The name is optional and it defaults to #false.

     format
          The image format as a symbol.  The following formats are supported:

            * disk-image, a raw disk image composed of one or multiple partitions.

            * compressed-qcow2, a compressed qcow2 image composed of one or multiple partitions.

            * docker, a Docker image.

            * iso9660, an ISO-9660 image.

            * tarball, a tar.gz image archive.

            * wsl2, a WSL2 image.

     platform (default: #false)
          The platform record the image is targeting (see Platforms), aarch64-linux for instance.  By default, this field is set to #false and the image will target the host platform.

     size (default: 'guess)
          The image size in bytes or 'guess.  The 'guess symbol, which is the default, means that the image size will be inferred based on the image content.

     operating-system
          The image's operating-system record that is instantiated.

     partition-table-type (default: 'mbr)
          The image partition table type as a symbol.  Possible values are 'mbr and 'gpt.  It default to 'mbr.

     partitions (default: '())
          The image partitions as a list of partition records (see partition Reference).

     compression? (default: #true)
          Whether the image content should be compressed, as a boolean.  It defaults to #true and only applies to 'iso9660 image formats.

     volatile-root? (default: #true)
          Whether the image root partition should be made volatile, as a boolean.

          This is achieved by using a RAM backed file system (overlayfs) that is mounted on top of the root partition by the initrd.  It defaults to #true.  When set to #false, the image root partition is mounted as read-write partition by the initrd.

     shared-store? (default: #false)
          Whether the image's store should be shared with the host system, as a boolean.  This can be useful when creating images dedicated to virtual machines.  When set to #false, which is the default, the image's operating-system closure is copied to the image.  Otherwise, when set to #true, it is assumed that the host store will be made available at boot, using a 9p mount for instance.

     shared-network? (default: #false)
          Whether to use the host network interfaces within the image, as a boolean.  This is only used for the 'docker image format.  It defaults to #false.

     substitutable? (default: #true)
          Whether the image derivation should be substitutable, as a boolean.  It defaults to true.

partition Reference
-------------------

In image record may contain some partitions.

 -- Data Type: partition
     This is the data type representing an image partition.

     size (default: 'guess)
          The partition size in bytes or 'guess.  The 'guess symbol, which is the default, means that the partition size will be inferred based on the partition content.

     offset (default: 0)
          The partition's start offset in bytes, relative to the image start or the previous partition end.  It defaults to 0 which means that there is no offset applied.

     file-system (default: "ext4")
          The partition file system as a string, defaulting to "ext4".  The supported values are "vfat", "fat16", "fat32" and "ext4".  "vfat", "fat16" and "fat32" partitions without the 'esp flag are by default LBA compatible.

     file-system-options (default: '())
          The partition file system creation options that should be passed to the partition creation tool, as a list of strings.  This is only supported when creating "ext4" partitions.

          See the "extended-options" man page section of the "mke2fs" tool for a more complete reference.

     label
          The partition label as a mandatory string, "my-root" for instance.

     uuid (default: #false)
          The partition UUID as an uuid record (see File Systems).  By default it is #false, which means that the partition creation tool will attribute a random UUID to the partition.

     flags (default: '())
          The partition flags as a list of symbols.  Possible values are 'boot and 'esp.  The 'boot flags should be set if you want to boot from this partition.  Exactly one partition should have this flag set, usually the root one. The 'esp flag identifies a UEFI System Partition.

     initializer (default: #false)
          The partition initializer procedure as a gexp.  This procedure is called to populate a partition.  If no initializer is passed, the initialize-root-partition procedure from the (gnu build image) module is used.

Instantiate an Image
====================

Let's say you would like to create an MBR image with three distinct partitions:

  * The ESP (EFI System Partition), a partition of 40 MiB at offset 1024 KiB with a vfat file system.

  * an ext4 partition of 50 MiB data file, and labeled ``data''.

  * an ext4 bootable partition containing the %simple-os operating-system.

You would then write the following image definition in a my-image.scm file for instance.

     (use-modules (gnu)
                  (gnu image)
                  (gnu tests)
                  (gnu system image)
                  (guix gexp))

     (define MiB (expt 2 20))

     (image
      (format 'disk-image)
      (operating-system %simple-os)
      (partitions
       (list
        (partition
         (size (* 40 MiB))
         (offset (* 1024 1024))
         (label "GNU-ESP")
         (file-system "vfat")
         (flags '(esp))
         (initializer (gexp initialize-efi-partition)))
        (partition
         (size (* 50 MiB))
         (label "DATA")
         (file-system "ext4")
         (initializer #~(lambda* (root . rest)
                          (mkdir root)
                          (call-with-output-file
                              (string-append root "/data")
                            (lambda (port)
                              (format port "my-data"))))))
        (partition
         (size 'guess)
         (label root-label)
         (file-system "ext4")
         (flags '(boot))
         (initializer (gexp initialize-root-partition))))))

Note that the first and third partitions use generic initializers procedures, initialize-efi-partition and initialize-root-partition respectively.  The initialize-efi-partition installs a GRUB EFI loader that is loading the GRUB bootloader located in the root partition.  The initialize-root-partition instantiates a complete system as defined by the %simple-os operating-system.

You can now run:

     guix system image my-image.scm

to instantiate the image definition.  That produces a disk image which has the expected structure:

     $ parted $(guix system image my-image.scm) print
     ...
     Model:  (file)
     Disk /gnu/store/yhylv1bp5b2ypb97pd3bbhz6jk5nbhxw-disk-image: 1714MB
     Sector size (logical/physical): 512B/512B
     Partition Table: msdos
     Disk Flags:

     Number  Start   End     Size    Type     File system  Flags
      1      1049kB  43.0MB  41.9MB  primary  fat16        esp
      2      43.0MB  95.4MB  52.4MB  primary  ext4
      3      95.4MB  1714MB  1619MB  primary  ext4         boot

The size of the boot partition has been inferred to 1619MB so that it is large enough to host the %simple-os operating-system.

You can also use existing image record definitions and inherit from them to simplify the image definition.  The (gnu system image) module provides the following image definition variables.

 -- Variable: mbr-disk-image
     An MBR disk-image composed of a single ROOT partition.  The ROOT partition starts at a 1 MiB offset so that the bootloader can install itself in the post-MBR gap.

 -- Variable: mbr-hybrid-disk-image
     An MBR disk-image composed of two partitions: a 64 bits ESP partition and a ROOT boot partition.  The ESP partition starts at a 1 MiB offset so that a BIOS compatible bootloader can install itself in the post-MBR gap.  The image can be used by x86_64 and i686 machines supporting only legacy BIOS booting.  The ESP partition ensures that it can also be used by newer machines relying on UEFI booting, hence the hybrid denomination.

 -- Variable: efi-disk-image
     A GPT disk-image composed of two partitions: a 64 bits ESP partition and a ROOT boot partition.  This image can be used on most x86_64 and i686 machines, supporting BIOS or UEFI booting.

 -- Variable: efi32-disk-image
     Same as efi-disk-image but with a 32 bits EFI partition.

 -- Variable: iso9660-image
     An ISO-9660 image composed of a single bootable partition.  This image can also be used on most x86_64 and i686 machines.

 -- Variable: docker-image
     A Docker image that can be used to spawn a Docker container.

Using the efi-disk-image we can simplify our previous image declaration this way:

     (use-modules (gnu)
                  (gnu image)
                  (gnu tests)
                  (gnu system image)
                  (guix gexp)
                  (ice-9 match))

     (define MiB (expt 2 20))

     (define data
       (partition
        (size (* 50 MiB))
        (label "DATA")
        (file-system "ext4")
        (initializer #~(lambda* (root . rest)
                         (mkdir root)
                         (call-with-output-file
                             (string-append root "/data")
                           (lambda (port)
                             (format port "my-data")))))))

     (image
      (inherit efi-disk-image)
      (operating-system %simple-os)
      (partitions
       (match (image-partitions efi-disk-image)
         ((esp root)
          (list esp data root)))))

This will give the exact same image instantiation but the image declaration is simpler.

image-type Reference
====================

The guix system image command can, as we saw above, take a file containing an image declaration as argument and produce an actual disk image from it.  The same command can also handle a file containing an operating-system declaration as argument.  In that case, how is the operating-system turned into an image?

That's where the image-type record intervenes.  This record defines how to transform an operating-system record into an image record.

 -- Data Type: image-type
     This is the data type representing an image-type.

     name
          The image-type name as a mandatory symbol, 'efi32-raw for instance.

     constructor
          The image-type constructor, as a mandatory procedure that takes an operating-system record as argument and returns an image record.

There are several image-type records provided by the (gnu system image) and the (gnu system images ...) modules.

 -- Variable: mbr-raw-image-type
     Build an image based on the mbr-disk-image image.

 -- Variable: mbr-hybrid-raw-image-type
     Build an image based on the mbr-hybrid-disk-image image.

 -- Variable: efi-raw-image-type
     Build an image based on the efi-disk-image image.

 -- Variable: efi32-raw-image-type
     Build an image based on the efi32-disk-image image.

 -- Variable: qcow2-image-type
     Build an image based on the mbr-disk-image image but with the compressed-qcow2 image format.

 -- Variable: iso-image-type
     Build a compressed image based on the iso9660-image image.

 -- Variable: uncompressed-iso-image-type
     Build an image based on the iso9660-image image but with the compression? field set to #false.

 -- Variable: docker-image-type
     Build an image based on the docker-image image.

 -- Variable: raw-with-offset-image-type
     Build an MBR image with a single partition starting at a 1024KiB offset.  This is useful to leave some room to install a bootloader in the post-MBR gap.

 -- Variable: pinebook-pro-image-type
     Build an image that is targeting the Pinebook Pro machine.  The MBR image contains a single partition starting at a 9MiB offset.  The u-boot-pinebook-pro-rk3399-bootloader bootloader will be installed in this gap.

 -- Variable: rock64-image-type
     Build an image that is targeting the Rock64 machine.  The MBR image contains a single partition starting at a 16MiB offset.  The u-boot-rock64-rk3328-bootloader bootloader will be installed in this gap.

 -- Variable: novena-image-type
     Build an image that is targeting the Novena machine.  It has the same characteristics as raw-with-offset-image-type.

 -- Variable: pine64-image-type
     Build an image that is targeting the Pine64 machine.  It has the same characteristics as raw-with-offset-image-type.

 -- Variable: hurd-image-type
     Build an image that is targeting a i386 machine running the Hurd kernel.  The MBR image contains a single ext2 partitions with specific file-system-options flags.

 -- Variable: hurd-qcow2-image-type
     Build an image similar to the one built by the hurd-image-type but with the format set to 'compressed-qcow2.

 -- Variable: wsl2-image-type
     Build an image for the WSL2 (Windows Subsystem for Linux 2). It can be imported by running:

          wsl --import Guix ./guix ./wsl2-image.tar.gz
          wsl -d Guix

So, if we get back to the guix system image command taking an operating-system declaration as argument.  By default, the mbr-raw-image-type is used to turn the provided operating-system into an actual bootable image.

To use a different image-type, the --image-type option can be used.  The --list-image-types option will list all the supported image types.  It turns out to be a textual listing of all the image-types variables described just above (see Invoking guix system).

Image Modules
=============

Let's take the example of the Pine64, an ARM based machine.  To be able to produce an image targeting this board, we need the following elements:

  * An operating-system record containing at least an appropriate kernel (linux-libre-arm64-generic) and bootloader u-boot-pine64-lts-bootloader) for the Pine64.

  * Possibly, an image-type record providing a way to turn an operating-system record to an image record suitable for the Pine64.

  * An actual image that can be instantiated with the guix system image command.

The (gnu system images pine64) module provides all those elements: pine64-barebones-os, pine64-image-type and pine64-barebones-raw-image respectively.

The module returns the pine64-barebones-raw-image in order for users to be able to run:

     guix system image gnu/system/images/pine64.scm

Now, thanks to the pine64-image-type record declaring the 'pine64-raw image-type, one could also prepare a my-pine.scm file with the following content:

     (use-modules (gnu system images pine64))
     (operating-system
       (inherit pine64-barebones-os)
       (timezone "Europe/Athens"))

to customize the pine64-barebones-os, and run:

     $ guix system image --image-type=pine64-raw my-pine.scm

Note that there are other modules in the gnu/system/images directory targeting Novena, Pine64, PinebookPro and Rock64 machines.

Installing Debugging Files
**************************

Program binaries, as produced by the GCC compilers for instance, are typically written in the ELF format, with a section containing debugging information.  Debugging information is what allows the debugger, GDB, to map binary code to source code; it is required to debug a compiled program in good conditions.

This chapter explains how to use separate debug info when packages provide it, and how to rebuild packages with debug info when it's missing.

Separate Debug Info
===================

The problem with debugging information is that it takes up a fair amount of disk space.  For example, debugging information for the GNU C Library weighs in at more than 60 MiB.  Thus, as a user, keeping all the debugging info of all the installed programs is usually not an option. Yet, space savings should not come at the cost of an impediment to debugging---especially in the GNU system, which should make it easier for users to exert their computing freedom (see GNU Distribution).

Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a mechanism that allows users to get the best of both worlds: debugging information can be stripped from the binaries and stored in separate files.  GDB is then able to load debugging information from those files, when they are available (see Separate Debug Files (Debugging with GDB)).

The GNU distribution takes advantage of this by storing debugging information in the lib/debug sub-directory of a separate package output unimaginatively called debug (see Packages with Multiple Outputs).  Users can choose to install the debug output of a package when they need it.  For instance, the following command installs the debugging information for the GNU C Library and for GNU Guile:

     guix install glibc:debug guile:debug

GDB must then be told to look for debug files in the user's profile, by setting the debug-file-directory variable (consider setting it from the ~/.gdbinit file, see Startup (Debugging with GDB)):

     (gdb) set debug-file-directory ~/.guix-profile/lib/debug

From there on, GDB will pick up debugging information from the .debug files under ~/.guix-profile/lib/debug.

Below is an alternative GDB script which is useful when working with other profiles.  It takes advantage of the optional Guile integration in GDB.  This snippet is included by default on Guix System in the ~/.gdbinit file.

     guile
     (use-modules (gdb))
     (execute (string-append "set debug-file-directory "
                             (or (getenv "GDB_DEBUG_FILE_DIRECTORY")
                                 "~/.guix-profile/lib/debug")))
     end

In addition, you will most likely want GDB to be able to show the source code being debugged.  To do that, you will have to unpack the source code of the package of interest (obtained with guix build --source, see Invoking guix build), and to point GDB to that source directory using the directory command (see directory (Debugging with GDB)).

The debug output mechanism in Guix is implemented by the gnu-build-system (see Build Systems).  Currently, it is opt-in---debugging information is available only for the packages with definitions explicitly declaring a debug output.  To check whether a package has a debug output, use guix package --list-available (see Invoking guix package).

Read on for how to deal with packages lacking a debug output.

Rebuilding Debug Info
=====================

As we saw above, some packages, but not all, provide debugging info in a debug output.  What can you do when debugging info is missing? The --with-debug-info option provides a solution to that: it allows you to rebuild the package(s) for which debugging info is missing---and only those---and to graft those onto the application you're debugging.  Thus, while it's not as fast as installing a debug output, it is relatively inexpensive.

Let's illustrate that.  Suppose you're experiencing a bug in Inkscape and would like to see what's going on in GLib, a library that's deep down in its dependency graph.  As it turns out, GLib does not have a debug output and the backtrace GDB shows is all sadness:

     (gdb) bt
     #0  0x00007ffff5f92190 in g_getenv ()
        from /gnu/store/...-glib-2.62.6/lib/libglib-2.0.so.0
     #1  0x00007ffff608a7d6 in gobject_init_ctor ()
        from /gnu/store/...-glib-2.62.6/lib/libgobject-2.0.so.0
     #2  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@entry=1, argv=argv@entry=0x7fffffffcfd8,
         env=env@entry=0x7fffffffcfe8) at dl-init.c:72
     #3  0x00007ffff7fe2866 in call_init (env=0x7fffffffcfe8, argv=0x7fffffffcfd8, argc=1, l=<optimized out>)
         at dl-init.c:118

To address that, you install Inkscape linked against a variant GLib that contains debug info:

     guix install inkscape --with-debug-info=glib

This time, debugging will be a whole lot nicer:

     $ gdb --args sh -c 'exec inkscape'
     ...
     (gdb) b g_getenv
     Function "g_getenv" not defined.
     Make breakpoint pending on future shared library load? (y or [n]) y
     Breakpoint 1 (g_getenv) pending.
     (gdb) r
     Starting program: /gnu/store/...-profile/bin/sh -c exec\ inkscape
     ...
     (gdb) bt
     #0  g_getenv (variable=variable@entry=0x7ffff60c7a2e "GOBJECT_DEBUG") at ../glib-2.62.6/glib/genviron.c:252
     #1  0x00007ffff608a7d6 in gobject_init () at ../glib-2.62.6/gobject/gtype.c:4380
     #2  gobject_init_ctor () at ../glib-2.62.6/gobject/gtype.c:4493
     #3  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@entry=3, argv=argv@entry=0x7fffffffd088,
         env=env@entry=0x7fffffffd0a8) at dl-init.c:72
     ...

Much better!

Note that there can be packages for which --with-debug-info will not have the desired effect.  See --with-debug-info, for more information.

Using TeX and LaTeX
*******************

Guix provides packages for the TeX, LaTeX, ConTeXt, LuaTeX, and related typesetting systems, taken from the TeX Live distribution (https://www.tug.org/texlive/).  However, because TeX Live is so huge and because finding one's way in this maze is tricky, so this section provides some guidance on how to deploy the relevant packages to compile TeX and LaTeX documents.

TeX Live currently comes in two mutually exclusive flavors in Guix:

  * The ``monolithic'' texlive package: it comes with every single TeX Live package (roughly 4,200), but it is huge---more than 4 GiB for a single package!

  * A ``modular'' TeX Live distribution, in which you only install the packages, always prefixed with texlive-, you need.

So to insist, these two flavors cannot be combined (No rule without exception! As the monolithic TeX Live does not contain the biber executable, it is okay to combine it with texlive-biber, which does.).  If in the modular setting your document does not compile, the solution is not to add the monolithic texlive package, but to add the set of missing packages from the modular distribution.

Building a coherent system that provides all the essential tools and, at the same time, satisfies all of its internal dependencies can be a difficult task.  It is therefore recommended to start with sets of packages, called collections, and schemes, the name for collections of collections.  The following command lists available schemes and collections (see Invoking guix package):

     guix search texlive-\(scheme\|collection\) | recsel -p name,description

If needed, you may then complete your system with individual packages, particularly when they belong to a large collection you're not otherwise interested in.

For instance, the following manifest is a reasonable, yet frugal starting point for a French LaTeX user:

     (specifications->manifest
      '("rubber"

        "texlive-scheme-basic"
        "texlive-collection-latexrecommended"
        "texlive-collection-fontsrecommended"
        "texlive-babel-french"

        ;; From "latexextra" collection.
        "texlive-tabularray"
        ;; From "binextra" collection.
        "texlive-texdoc"))

If you come across a document that does not compile in such a basic setting, the main difficulty is finding the missing packages.  In this case, pdflatex and similar commands tend to fail with obscure error messages along the lines of:

     doc.tex: File `tikz.sty' not found.
     doc.tex:7: Emergency stop.

or, for a missing font:

     kpathsea: Running mktexmf phvr7t
     ! I can't find file `phvr7t'.

How do you determine what the missing package is?  In the first case, you will find the answer by running:

     $ guix search texlive tikz
     name: texlive-pgf
     version: 59745
     ...

In the second case, guix search turns up nothing.  Instead, you can search the TeX Live package database using the tlmgr command:

     $ tlmgr info phvr7t
     tlmgr: cannot find package phvr7t, searching for other matches:

     Packages containing `phvr7t' in their title/description:

     Packages containing files matching `phvr7t':
     helvetic:
             texmf-dist/fonts/tfm/adobe/helvetic/phvr7t.tfm
             texmf-dist/fonts/tfm/adobe/helvetic/phvr7tn.tfm
             texmf-dist/fonts/vf/adobe/helvetic/phvr7t.vf
             texmf-dist/fonts/vf/adobe/helvetic/phvr7tn.vf
     tex4ht:
             texmf-dist/tex4ht/ht-fonts/alias/adobe/helvetic/phvr7t.htf

The file is available in the TeX Live helvetic package, which is known in Guix as texlive-helvetic.  Quite a ride, but you found it!

Security Updates
****************

Occasionally, important security vulnerabilities are discovered in software packages and must be patched.  Guix developers try hard to keep track of known vulnerabilities and to apply fixes as soon as possible in the master branch of Guix (we do not yet provide a ``stable'' branch containing only security updates).  The guix lint tool helps developers find out about vulnerable versions of software packages in the distribution:

     $ guix lint -c cve
     gnu/packages/base.scm:652:2: glibc@2.21: probably vulnerable to CVE-2015-1781, CVE-2015-7547
     gnu/packages/gcc.scm:334:2: gcc@4.9.3: probably vulnerable to CVE-2015-5276
     gnu/packages/image.scm:312:2: openjpeg@2.1.0: probably vulnerable to CVE-2016-1923, CVE-2016-1924
     ...

See Invoking guix lint, for more information.

Guix follows a functional package management discipline (see Introduction), which implies that, when a package is changed, every package that depends on it must be rebuilt.  This can significantly slow down the deployment of fixes in core packages such as libc or Bash, since basically the whole distribution would need to be rebuilt.  Using pre-built binaries helps (see Substitutes), but deployment may still take more time than desired.

To address this, Guix implements grafts, a mechanism that allows for fast deployment of critical updates without the costs associated with a whole-distribution rebuild.  The idea is to rebuild only the package that needs to be patched, and then to ``graft'' it onto packages explicitly installed by the user and that were previously referring to the original package.  The cost of grafting is typically very low, and order of magnitudes lower than a full rebuild of the dependency chain.

For instance, suppose a security update needs to be applied to Bash. Guix developers will provide a package definition for the ``fixed'' Bash, say bash-fixed, in the usual way (see Defining Packages).  Then, the original package definition is augmented with a replacement field pointing to the package containing the bug fix:

     (define bash
       (package
         (name "bash")
         ;; ...
         (replacement bash-fixed)))

From there on, any package depending directly or indirectly on Bash---as reported by guix gc --requisites (see Invoking guix gc)---that is installed is automatically ``rewritten'' to refer to bash-fixed instead of bash.  This grafting process takes time proportional to the size of the package, usually less than a minute for an ``average'' package on a recent machine.  Grafting is recursive: when an indirect dependency requires grafting, then grafting ``propagates'' up to the package that the user is installing.

Currently, the length of the name and version of the graft and that of the package it replaces (bash-fixed and bash in the example above) must be equal.  This restriction mostly comes from the fact that grafting works by patching files, including binary files, directly. Other restrictions may apply: for instance, when adding a graft to a package providing a shared library, the original shared library and its replacement must have the same SONAME and be binary-compatible.

The --no-grafts command-line option allows you to forcefully avoid grafting (see --no-grafts). Thus, the command:

     guix build bash --no-grafts

returns the store file name of the original Bash, whereas:

     guix build bash

returns the store file name of the ``fixed'', replacement Bash.  This allows you to distinguish between the two variants of Bash.

To verify which Bash your whole profile refers to, you can run (see Invoking guix gc):

     guix gc -R $(readlink -f ~/.guix-profile) | grep bash

... and compare the store file names that you get with those above. Likewise for a complete Guix system generation:

     guix gc -R $(guix system build my-config.scm) | grep bash

Lastly, to check which Bash running processes are using, you can use the lsof command:

     lsof | grep /gnu/store/.*bash

Bootstrapping
*************

Bootstrapping in our context refers to how the distribution gets built ``from nothing''.  Remember that the build environment of a derivation contains nothing but its declared inputs (see Introduction).  So there's an obvious chicken-and-egg problem: how does the first package get built?  How does the first compiler get compiled?

It is tempting to think of this question as one that only die-hard hackers may care about.  However, while the answer to that question is technical in nature, its implications are wide-ranging.  How the distribution is bootstrapped defines the extent to which we, as individuals and as a collective of users and hackers, can trust the software we run.  It is a central concern from the standpoint of security and from a user freedom viewpoint.

The GNU system is primarily made of C code, with libc at its core.  The GNU build system itself assumes the availability of a Bourne shell and command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and `grep'.  Furthermore, build programs---programs that run ./configure, make, etc.---are written in Guile Scheme (see Derivations).  Consequently, to be able to build anything at all, from scratch, Guix relies on pre-built binaries of Guile, GCC, Binutils, libc, and the other packages mentioned above---the bootstrap binaries.

These bootstrap binaries are ``taken for granted'', though we can also re-create them if needed (see Preparing to Use the Bootstrap Binaries).

The Full-Source Bootstrap
=========================

Guix---like other GNU/Linux distributions---is traditionally bootstrapped from a set of bootstrap binaries: Bourne shell, command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and `grep' and Guile, GCC, Binutils, and the GNU C Library (see Bootstrapping).  Usually, these bootstrap binaries are ``taken for granted.''

Taking the bootstrap binaries for granted means that we consider them to be a correct and trustworthy ``seed'' for building the complete system. Therein lies a problem: the combined size of these bootstrap binaries is about 250MB (see Bootstrappable Builds (GNU Mes)).  Auditing or even inspecting these is next to impossible.

For i686-linux and x86_64-linux, Guix now features a full-source bootstrap.  This bootstrap is rooted in hex0-seed from the Stage0 (https://savannah.gnu.org/projects/stage0) package.  The hex0 program is minimalist assembler: it reads space-separated hexadecimal digits (nibbles) from a file, possibly including comments, and emits on standard output the bytes corresponding to those hexadecimal numbers.  The source code of this initial hex0 program is a file called hex0_x86.hex0 (https://github.com/oriansj/bootstrap-seeds/blob/master/POSIX/x86/hex0_x86.hex0) and is written in the hex0 language.

Hex0 is self-hosting, which means that it can build itself:

     ./hex0-seed hex0_x86.hex0 hex0

Hex0 it is the ASCII-equivalent of the binary program and can be produced by doing something much like:

     sed 's/[;#].*$//g' hex0_x86.hex0 | xxd -r -p > hex0
     chmod +x hex0

It is because of this ASCII-binary equivalence that we can bless this initial 357-byte binary as source, and hence `full-source bootstrap''.

The bootstrap then continues: hex0 builds hex1 and then on to M0, hex2, M1, mescc-tools and finally M2-Planet.  Then, using mescc-tools, M2-Planet we build Mes (see GNU Mes Reference Manual (GNU Mes), a Scheme interpreter and C compiler in Scheme).  From here on starts the more traditional C-based bootstrap of the GNU System.

Another step that Guix has taken is to replace the shell and all its utilities with implementations in Guile Scheme, the Scheme-only bootstrap.  Gash (see Gash (The Gash manual)) is a POSIX-compatible shell that replaces Bash, and it comes with Gash Utils which has minimalist replacements for Awk, the GNU Core Utilities, Grep, Gzip, Sed, and Tar.

Building the GNU System from source is currently only possible by adding some historical GNU packages as intermediate steps (Packages such as gcc-2.95.3, binutils-2.14, glibc-2.2.5, gzip-1.2.4, tar-1.22, and some others.  For details, see gnu/packages/commencement.scm.).  As Gash and Gash Utils mature, and GNU packages become more bootstrappable again (e.g., new releases of GNU Sed will also ship as gzipped tarballs again, as alternative to the hard to bootstrap xz-compression), this set of added packages can hopefully be reduced again.

The graph below shows the resulting dependency graph for gcc-core-mesboot0, the bootstrap compiler used for the traditional bootstrap of the rest of the Guix System.

Dependency graph of gcc-core-mesboot0

Work is ongoing to bring these bootstraps to the arm-linux and aarch64-linux architectures and to the Hurd.

If you are interested, join us on #bootstrappable on the Libera.Chat IRC network or discuss on bug-mes@gnu.org or gash-devel@nongnu.org.

Preparing to Use the Bootstrap Binaries
=======================================

Dependency graph of the early bootstrap derivations

The figure above shows the very beginning of the dependency graph of the distribution, corresponding to the package definitions of the (gnu packages bootstrap) module.  A similar figure can be generated with guix graph (see Invoking guix graph), along the lines of:

     guix graph -t derivation \
       -e '(@@ (gnu packages bootstrap) %bootstrap-gcc)' \
       | dot -Tps > gcc.ps

or, for the further Reduced Binary Seed bootstrap

     guix graph -t derivation \
       -e '(@@ (gnu packages bootstrap) %bootstrap-mes)' \
       | dot -Tps > mes.ps

At this level of detail, things are slightly complex.  First, Guile itself consists of an ELF executable, along with many source and compiled Scheme files that are dynamically loaded when it runs.  This gets stored in the guile-2.0.7.tar.xz tarball shown in this graph.  This tarball is part of Guix's ``source'' distribution, and gets inserted into the store with add-to-store (see The Store).

But how do we write a derivation that unpacks this tarball and adds it to the store?  To solve this problem, the guile-bootstrap-2.0.drv derivation---the first one that gets built---uses bash as its builder, which runs build-bootstrap-guile.sh, which in turn calls tar to unpack the tarball.  Thus, bash, tar, xz, and mkdir are statically-linked binaries, also part of the Guix source distribution, whose sole purpose is to allow the Guile tarball to be unpacked.

Once guile-bootstrap-2.0.drv is built, we have a functioning Guile that can be used to run subsequent build programs.  Its first task is to download tarballs containing the other pre-built binaries---this is what the .tar.xz.drv derivations do.  Guix modules such as ftp-client.scm are used for this purpose.  The module-import.drv derivations import those modules in a directory in the store, using the original layout.  The module-import-compiled.drv derivations compile those modules, and write them in an output directory with the right layout.  This corresponds to the #:modules argument of build-expression->derivation (see Derivations).

Finally, the various tarballs are unpacked by the derivations gcc-bootstrap-0.drv, glibc-bootstrap-0.drv, or bootstrap-mes-0.drv and bootstrap-mescc-tools-0.drv, at which point we have a working C tool chain.

Building the Build Tools
========================

Bootstrapping is complete when we have a full tool chain that does not depend on the pre-built bootstrap tools discussed above.  This no-dependency requirement is verified by checking whether the files of the final tool chain contain references to the /gnu/store directories of the bootstrap inputs.  The process that leads to this ``final'' tool chain is described by the package definitions found in the (gnu packages commencement) module.

The guix graph command allows us to ``zoom out'' compared to the graph above, by looking at the level of package objects instead of individual derivations---remember that a package may translate to several derivations, typically one derivation to download its source, one to build the Guile modules it needs, and one to actually build the package from source.  The command:

     guix graph -t bag \
       -e '(@@ (gnu packages commencement)
               glibc-final-with-bootstrap-bash)' | xdot -

displays the dependency graph leading to the ``final'' C library (You may notice the glibc-intermediate label, suggesting that it is not quite final, but as a good approximation, we will consider it final.), depicted below.

Dependency graph of the early packages

The first tool that gets built with the bootstrap binaries is GNU Make---noted make-boot0 above---which is a prerequisite for all the following packages.  From there Findutils and Diffutils get built.

Then come the first-stage Binutils and GCC, built as pseudo cross tools---i.e., with --target equal to --host.  They are used to build libc.  Thanks to this cross-build trick, this libc is guaranteed not to hold any reference to the initial tool chain.

From there the final Binutils and GCC (not shown above) are built.  GCC uses ld from the final Binutils, and links programs against the just-built libc.  This tool chain is used to build the other packages used by Guix and by the GNU Build System: Guile, Bash, Coreutils, etc.

And voilà!  At this point we have the complete set of build tools that the GNU Build System expects.  These are in the %final-inputs variable of the (gnu packages commencement) module, and are implicitly used by any package that uses gnu-build-system (see gnu-build-system).

Building the Bootstrap Binaries
===============================

Because the final tool chain does not depend on the bootstrap binaries, those rarely need to be updated.  Nevertheless, it is useful to have an automated way to produce them, should an update occur, and this is what the (gnu packages make-bootstrap) module provides.

The following command builds the tarballs containing the bootstrap binaries (Binutils, GCC, glibc, for the traditional bootstrap and linux-libre-headers, bootstrap-mescc-tools, bootstrap-mes for the Reduced Binary Seed bootstrap, and Guile, and a tarball containing a mixture of Coreutils and other basic command-line tools):

     guix build bootstrap-tarballs

The generated tarballs are those that should be referred to in the (gnu packages bootstrap) module mentioned at the beginning of this section.

Still here?  Then perhaps by now you've started to wonder: when do we reach a fixed point?  That is an interesting question!  The answer is unknown, but if you would like to investigate further (and have significant computational and storage resources to do so), then let us know.

Reducing the Set of Bootstrap Binaries
======================================

Our traditional bootstrap includes GCC, GNU Libc, Guile, etc.  That's a lot of binary code!  Why is that a problem?  It's a problem because these big chunks of binary code are practically non-auditable, which makes it hard to establish what source code produced them.  Every unauditable binary also leaves us vulnerable to compiler backdoors as described by Ken Thompson in the 1984 paper Reflections on Trusting Trust.

This is mitigated by the fact that our bootstrap binaries were generated from an earlier Guix revision.  Nevertheless it lacks the level of transparency that we get in the rest of the package dependency graph, where Guix always gives us a source-to-binary mapping.  Thus, our goal is to reduce the set of bootstrap binaries to the bare minimum.

The Bootstrappable.org web site (https://bootstrappable.org) lists on-going projects to do that.  One of these is about replacing the bootstrap GCC with a sequence of assemblers, interpreters, and compilers of increasing complexity, which could be built from source starting from a simple and auditable assembler.

Our first major achievement is the replacement of GCC, the GNU C Library and Binutils by MesCC-Tools (a simple hex linker and macro assembler) and Mes (see GNU Mes Reference Manual (GNU Mes), a Scheme interpreter and C compiler in Scheme).  Neither MesCC-Tools nor Mes can be fully bootstrapped yet and thus we inject them as binary seeds.  We call this the Reduced Binary Seed bootstrap, as it has halved the size of our bootstrap binaries!  Also, it has eliminated the C compiler binary; i686-linux and x86_64-linux Guix packages are now bootstrapped without any binary C compiler.

Work is ongoing to make MesCC-Tools and Mes fully bootstrappable and we are also looking at any other bootstrap binaries.  Your help is welcome!

Porting to a New Platform
*************************

As discussed above, the GNU distribution is self-contained, and self-containment is achieved by relying on pre-built ``bootstrap binaries'' (see Bootstrapping).  These binaries are specific to an operating system kernel, CPU architecture, and application binary interface (ABI).  Thus, to port the distribution to a platform that is not yet supported, one must build those bootstrap binaries, and update the (gnu packages bootstrap) module to use them on that platform.

Fortunately, Guix can cross compile those bootstrap binaries. When everything goes well, and assuming the GNU tool chain supports the target platform, this can be as simple as running a command like this one:

     guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs

For this to work, it is first required to register a new platform as defined in the (guix platform) module.  A platform is making the connection between a GNU triplet (see GNU configuration triplets (Autoconf)), the equivalent SYSTEM in Nix notation, the name of the GLIBC-DYNAMIC-LINKER, and the corresponding Linux architecture name if applicable (see Platforms).

Once the bootstrap tarball are built, the (gnu packages bootstrap) module needs to be updated to refer to these binaries on the target platform.  That is, the hashes and URLs of the bootstrap tarballs for the new platform must be added alongside those of the currently supported platforms.  The bootstrap Guile tarball is treated specially: it is expected to be available locally, and gnu/local.mk has rules to download it for the supported architectures; a rule for the new platform must be added as well.

In practice, there may be some complications.  First, it may be that the extended GNU triplet that specifies an ABI (like the eabi suffix above) is not recognized by all the GNU tools.  Typically, glibc recognizes some of these, whereas GCC uses an extra --with-abi configure flag (see gcc.scm for examples of how to handle this). Second, some of the required packages could fail to build for that platform.  Lastly, the generated binaries could be broken for some reason.

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Acknowledgments
***************

Guix is based on the Nix package manager (https://nixos.org/nix/), which was designed and implemented by Eelco Dolstra, with contributions from other people (see the nix/AUTHORS file in Guix).  Nix pioneered functional package management, and promoted unprecedented features, such as transactional package upgrades and rollbacks, per-user profiles, and referentially transparent build processes.  Without this work, Guix would not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been an inspiration for Guix.

GNU Guix itself is a collective work with contributions from a number of people.  See the AUTHORS file in Guix for more information on these fine people.  The THANKS file lists people who have helped by reporting bugs, taking care of the infrastructure, providing artwork and themes, making suggestions, and more---thank you!

GNU Free Documentation License
******************************

     [file fdl-1.3.texi not included]