     [file version.texi not included]

Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès

Copyright © 2013, 2014 Andreas Enge

Copyright © 2013 Nikita Karetnikov

Copyright © 2015 Mathieu Lirzin

Copyright © 2014 Pierre-Antoine Rault

Copyright © 2015 Taylan Ulrich Bayırlı/Kammer

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license is included in the section entitled ``GNU Free Documentation License''.

GNU Guix
********

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

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

GNU Guix (``Guix'' is pronounced like ``geeks'', or ``ɡiːks'' using the international phonetic alphabet (IPA).) is a functional package management tool for the GNU system.  Package management consists of all activities that relate to building packages from sources, honoring their build-time and run-time dependencies, installing packages in user environments, upgrading installed packages to new versions or rolling back to a previous set, removing unused software packages, etc.

The term functional refers to a specific package management discipline.  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 system's environment 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 of Guix's salient features: support for transactional package upgrade and rollback, per-user installation, and garbage collection of packages (see Features).

Guix has a command-line interface, which allows users to build, install, upgrade, and remove packages, as well as a Scheme programming interface.

Last but not least, Guix is used to build a distribution of the GNU system, with many GNU and non-GNU free software packages.  The Guix System Distribution, or GNU GuixSD, takes advantage of the core properties of Guix at the system level.  With GuixSD, users declare all aspects of the operating system configuration, and Guix takes care of instantiating that configuration in a reproducible, stateless fashion.  See GNU Distribution.

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

GNU Guix is available for download from its website at http://www.gnu.org/software/guix/.  This section describes the software requirements of Guix, as well as how to install it and get ready to use it.

Note that 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.

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.

Installing goes along these lines:

 1. Download the binary tarball from ftp://alpha.gnu.org/gnu/guix/guix-binary-VERSION.SYSTEM.tar.xz (As
     usual, make sure to download the associated .sig file and to
     verify the authenticity of the tarball against it!), where SYSTEM is x86_64-linux for an x86_64 machine already running the kernel Linux, and so on.

 2. As root, run:

          # cd /tmp
          # tar xf guix-binary-VERSION.SYSTEM.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.

 3. Make root's profile available under ~/.guix-profile:

          # ln -sf /var/guix/profiles/per-user/root/guix-profile \
                   ~root/.guix-profile

 4. Run the daemon:

          # ~root/.guix-profile/bin/guix-daemon --build-users-group=guixbuild

 5. 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/guix-profile/bin/guix

 6. To use substitutes from hydra.gnu.org (see Substitutes), authorize them:

          # guix archive --authorize < ~root/.guix-profile/share/guix/hydra.gnu.org.pub

And that's it!

The guix package must remain available in root's profile, or it would become subject to garbage collection---in which case you would find yourself badly handicapped by the lack of the guix command.

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

     make guix-binary.SYSTEM.tar.xz

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 depends on the following packages:

  * GNU Guile (http://gnu.org/software/guile/), version 2.0.7 or later;

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

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

The following dependencies are optional:

  * Installing Guile-JSON (http://savannah.nongnu.org/projects/guile-json/) will allow you to use the guix import pypi command (see Invoking guix import).  It is of interest primarily for developers and not for casual users.

  * Installing GnuTLS-Guile (http://gnutls.org/) will allow you to access https URLs with the guix download command (see Invoking guix download), the guix import pypi command, and the guix import cpan command.  This is primarily of interest to developers.  See how to install the GnuTLS bindings for Guile (GnuTLS-Guile).

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

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

  * libbz2 (http://www.bzip.org);

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

When a working installation of the Nix package manager (http://nixos.org/nix/) is available, you can instead configure Guix with --disable-daemon.  In that case, Nix replaces the three dependencies above.

Guix is compatible with Nix, so it is possible to share the same store between both.  To do so, you must pass configure not only the same --with-store-dir value, but also the same --localstatedir value.  The latter is essential because it specifies where the database that stores metadata about the store is located, among other things.  The default values for Nix are --with-store-dir=/nix/store and --localstatedir=/nix/var. Note that --disable-daemon is not required if your goal is to share the store with Nix.

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.

Upon failure, please email bug-guix@gnu.org and attach the test-suite.log file.  When tests/SOMETHING.scm fails, please also attach the SOMETHING.log file available in the top-level build directory.  Please specify the Guix version being used as well as version numbers of the dependencies (see Requirements) in your message.

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.  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). The guix-daemon program may then be run as root with:

     # 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 container's processes 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.

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.  When that feature is enabled, a list of user-specified build machines is read from /etc/guix/machines.scm; anytime a build is requested, for instance via guix build, the daemon attempts to offload it to one of the machines that satisfies the derivation's constraints, in particular its system type---e.g., x86_64-linux.  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 /etc/guix/machines.scm file typically looks like this:

     (list (build-machine
             (name "eightysix.example.org")
             (system "x86_64-linux")
             (user "bob")
             (speed 2.))    ; incredibly fast!

           (build-machine
             (name "meeps.example.org")
             (system "mips64el-linux")
             (user "alice")
             (private-key
              (string-append (getenv "HOME")
                             "/.lsh/identity-for-guix"))))

In the example above we specify a list of two build machines, one for the x86_64 architecture and one for the mips64el 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 the daemon may offload builds to.  The important fields are:

     name
          The remote machine's host name.

     system
          The remote machine's system type---e.g., "x86_64-linux".

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

     A number of optional fields may be specified:

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

     private-key
          The SSH private key file to use when connecting to the machine.

          Currently offloading uses GNU lsh as its SSH client (see Invoking lsh (GNU lsh Manual)).  Thus, the key file here must be an lsh key file.  This may change in the future, though.

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

     speed
          A ``relative speed factor''.  The offload scheduler will tend to prefer machines with a higher speed factor.

     features
          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.

The guix command must be in the search path on the build machines, since offloading works by invoking the guix archive and guix build commands.  In addition, the Guix modules must be in $GUILE_LOAD_PATH on the build machine---you can check whether this is the case by running:

     lsh build-machine guile -c '(use-modules (guix config))'

There's 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

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.

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

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.  Be aware that using a directory other than /tmp can affect build results---for example, with a longer directory name, a build process that uses Unix-domain sockets might hit the name length limitation for sun_path, which it would otherwise not hit.

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

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).

     By default substitutes are used, unless the client---such as the guix package command---is explicitly invoked with --no-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, http://hydra.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).

--no-build-hook
     Do not use the build hook.

     The build hook is a helper program that the daemon can start and to which it submits build requests.  This mechanism is used to offload builds to other machines (see Daemon Offload Setup).

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

--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.

--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.

--disable-log-compression
     Disable compression of the build logs.

     Unless --lose-logs is used, all the build logs are kept in the LOCALSTATEDIR.  To save space, the daemon automatically compresses them with bzip2 by default.  This option disables that.

--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 increasde 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 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.

     Note that when both --gc-keep-derivations and --gc-keep-outputs are used, 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 live.  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=SOCKET
     Listen for connections on SOCKET, the file name of a Unix-domain socket.  The default socket is LOCALSTATEDIR/daemon-socket/socket.  This option is only useful in exceptional circumstances, such as if you need to run several daemons on the same machine.

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

When using Guix on top of GNU/Linux distribution other than GuixSD, 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 host system's locale data.  Instead, you must first install one of the locale packages available with Guix and then define the LOCPATH environment variable (see LOCPATH (The GNU C Library Reference Manual)):

     $ guix package -i glibc-locales
     $ export 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 110 MiB.  Alternately, the glibc-utf8-locales is smaller but limited to a few UTF-8 locales.

X11 Fonts
---------

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

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 procedure 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.  Two user interfaces are provided for routine package management tasks: a command-line interface (see guix package), and a visual user interface in Emacs (see Emacs Interface).

Features
========

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 (note that Guix comes with an Emacs extension to shorten those file names, see Emacs Prettify.)

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 those 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 is subject to transactional upgrades and roll-back (see Using the Configuration System).

All those packages in the package store may be garbage-collected. Guix can determine which packages are still referenced by the 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.

Finally, 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).

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

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.  It 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

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 the Guix System Distribution, 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="$HOME/.guix-profile" \
     source "$HOME/.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/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 either a simple package name, such as guile, or a package name followed by a hyphen and version number, such as guile-1.8.8 or simply guile-1.8 (in the latter case, the newest version prefixed by 1.8 is selected.)

     If no version number is specified, the newest available version will be selected.  In addition, PACKAGE 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).

     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 independently.

     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.

     Finally, when installing a GNU package, the tool reports the availability of a newer upstream version.  In the future, it may provide the option of installing directly from the upstream version, even if that version is not yet in the distribution.

--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.

--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).

--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 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")))

--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 meta-data.

     Installing, removing, or upgrading packages from a generation that has been rolled back to overwrites previous future generations.  Thus, the history of a profile's generations 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.

     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.

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

--verbose
     Produce verbose output.  In particular, emit the environment's build log on the standard error port.

--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.  Print all the meta-data 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
          name: glibc
          version: 2.17

          name: libgc
          version: 7.2alpha6

     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
          ...

--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=python | recsel -p name,version
          name: python
          version: 2.7.6

          name: python
          version: 3.3.5

     You may also specify the full name of a package to only get details about a specific version of it:

          $ guix package --show=python-3.3.5 | recsel -p name,version
          name: python
          version: 3.3.5

--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 installed 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 lesser 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 roll-back to them. Consequently, this command must be used with care.

Finally, since guix package may actually start build processes, it supports all the common build options that guix build supports (see common build options).

     [file emacs.texi not included]

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

Guix supports transparent source/binary deployment, which means that it can either build things locally, or download pre-built items from a server.  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.

The hydra.gnu.org server is a front-end to a build farm that builds packages from the GNU distribution continuously for some architectures, and makes them available as substitutes.  This is the default source of substitutes; it can be overridden by passing guix-daemon the --substitute-urls option (see Invoking guix-daemon).

To allow Guix to download substitutes from hydra.gnu.org, you must add its 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 hydra.gnu.org to not be compromised and to serve genuine substitutes.

This public key is installed along with Guix, in PREFIX/share/guix/hydra.gnu.org.pub, 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 < hydra.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
     The following files 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
     ...

This indicates that substitutes from hydra.gnu.org are usable and will be downloaded, when possible, for future builds.

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

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.

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 hydra.gnu.org substitutes can be convenient, we encourage users to also build on their own, or even run their own build farm, such that hydra.gnu.org is 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.

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 exactly one directory in the store.  When running guix package -i 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 package -i glib

The command to install its documentation is:

     guix package -i glib:doc

Some packages install programs with different ``dependency footprints''. For instance, the WordNet package install 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).

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 packages are listed in the third column of the output of guix package --list-available (see Invoking guix package).

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 includes default user profiles, and may be augmented with guix build --root, for example (see Invoking guix build).

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).

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.

--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-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 an element's closure.

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 daemon's database actually exist in /gnu/store.

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

     When passing --verify=contents, the daemon will compute the content hash of each store item and compare 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.

--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.

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.

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.

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

--verbose
     Produce verbose output, writing build logs to the standard error output.

--url=URL
     Download the source tarball of Guix from URL.

     By default, the tarball is taken from its canonical address at gnu.org, for the stable branch of Guix.

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

Invoking guix archive
=====================

The guix archive command allows users to export files from the store into a single archive, and to later import them. In particular, it allows store files to be transferred from one machine to another machine's store.  For example, 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 target machine's store.  The --missing option can help figure out which items are missing from the target's store.

Archives are stored in the ``Nix archive'' or ``Nar'' format, which is comparable in spirit to `tar', but with a few noteworthy differences that make it more appropriate for our purposes.  First, rather than recording all Unix meta-data 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.

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 daemons.  This is a prerequisite before archives can be exported with --export.  Note that this operation usually takes time, because it needs to gather enough entropy to generate the key pair.

     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. Alternately, 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'' (http://people.csail.mit.edu/rivest/Sexp.txt) and is structured as an access-control list in the Simple Public-Key Infrastructure (SPKI) (http://theworld.com/~cme/spki.txt).

To export store files as an archive to the 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 same options that can be passed to the guix build command (see common build options).

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 a 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.

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))

     (define-public hello
       (package
         (name "hello")
         (version "2.8")
         (source (origin
                  (method url-fetch)
                  (uri (string-append "mirror://gnu/hello/hello-" version
                                      ".tar.gz"))
                  (sha256
                   (base32 "0wqd8sjmxfskrflaxywc7gqw7sfawrfvdxd9skxawzfgyy0pzdz6"))))
         (build-system gnu-build-system)
         (arguments `(#:configure-flags '("--enable-silent-rules")))
         (inputs `(("gawk" ,gawk)))
         (synopsis "Hello, GNU world: An example GNU package")
         (description "Guess what GNU Hello prints!")
         (home-page "http://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 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 into 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.

  * 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.

  * The inputs field specifies inputs to the build process---i.e., build-time or run-time dependencies of the package.  Here, we define an input called "gawk" whose value is that of 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.

Once a package definition is in place, the package may actually be built using the guix build command-line tool (see Invoking guix build).  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.

Eventually, 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).

 -- Scheme 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:

 -- Scheme 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 "mips64el-linux-gnu" (see GNU configuration triplets (GNU Configure and Build System)).

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.

     source
          An origin object telling how the source code for the package should be acquired (see origin Reference).

     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.  This is a list, typically containing sequential keyword-value pairs.

     inputs (default: '())
          Package or derivation inputs to the build.  This is a list of lists, where each list has the name of the input (a string) as its first element, a package or derivation object as its second element, and optionally the name of the output of the package or derivation that should be used, which defaults to "out".

     propagated-inputs (default: '())
          This field is like inputs, but the specified packages will be force-installed 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 a library needs headers of another library to compile, or needs another shared library to be linked alongside itself when a program wants to link to it.

     native-inputs (default: '())
          This field is like inputs, but in case of a cross-compilation it will be ensured that packages for the architecture of the build machine are present, such that executables from them can be used during the build.

          This is typically where you would 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).

     self-native-input? (default: #f)
          This is a Boolean field telling whether the package should use itself as a native input when cross-compiling.

     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.

     replacement (default: #f)
          This must 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.

     license
          The license of the package; a value from (guix licenses).

     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".

     maintainers (default: '())
          The list of maintainers of the package, as maintainer objects.

     location (default: source location of the package form)
          The source location of the package.  It's useful to override this when inheriting from another package, in which case this field is not automatically corrected.

origin Reference
----------------

This section summarizes all the options available in origin declarations (see Defining Packages).

 -- 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 procedure that will handle the URI.

          Examples include:

          URL-FETCH from (guix download)
               download a file the HTTP, HTTPS, or FTP URL specified in the uri field;

          GIT-FETCH from (guix git-download)
               clone the Git version control repository, and check out the revision specified in the uri field as a git-reference object; a git-reference looks like this:

                    (git-reference
                      (url "git://git.debian.org/git/pkg-shadow/shadow")
                      (commit "v4.1.5.1"))

     sha256
          A bytevector containing the SHA-256 hash of the source.  Typically the base32 form is used here to generate the bytevector from a base-32 string.

     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's recommended to provide the file name explicitly because the default is not very descriptive.

     patches (default: '())
          A list of file names containing patches to be applied to the source.

     snippet (default: #f)
          A quoted piece of code that will be run in the source directory to make any modifications, which is 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.

     imported-modules (default: '())
          The list of Guile modules to import in the patch derivation, for use by the snippet.

     patch-guile (default: #f)
          The Guile package that should be used in the patching process.  When this is #f, a sensible default is used.

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 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).

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 packages and many other packages.  It is provided by the (guix build-system gnu) module.

 -- Scheme 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 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, notably (Please see the (guix build gnu-build-system) modules for more details about the build phases.):

     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-builds? 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).

     The build-side module (guix build gnu-build-system) defines %STANDARD-PHASES as the default list of build phases. %STANDARD-PHASES is a list of symbol/procedure pairs, where the procedure implements the actual phase.

     The list of phases used for a particular package can be changed with the #:phases parameter.  For instance, passing:

          #:phases (alist-delete 'configure %standard-phases)

     means that all the phases described above will be used, except the configure phase.

     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 don't have to mention them.

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.

 -- Scheme 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 (http://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.

 -- Scheme 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 found under bin/ are able to find GLib's ``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 GLib's GSettings schemas (https://developer.gnome.org/gio/stable/glib-compile-schemas.html) 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.

 -- Scheme 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 their PYTHONPATH environment variable points to all the Python libraries they depend on.

     Which Python package is used can be specified with the #:python parameter.

 -- Scheme 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.

 -- Scheme 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.

     Which Ruby package is used can be specified with the #:ruby parameter.

 -- Scheme 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.

 -- Scheme 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.

 -- Scheme Variable: emacs-build-system
     This variable is exported by (guix build-system emacs).  It implements an installation procedure similar to the one of Emacs' own packaging system (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.  Each package is installed in its own directory under share/emacs/site-lisp/guix.d.

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.

 -- Scheme 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's output(s)---as with build-expression->derivation (see build-expression->derivation).

The Store
=========

Conceptually, the store is where derivations that have been successfully built are stored---by default, under /gnu/store. Sub-directories in the store are referred to as store paths.  The store has an associated database that contains information such has the store paths referred to by each store path, and the list of valid store paths---paths that result from a successful build.

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 it requests, and read the result---these are remote procedure calls, or RPCs.

The (guix store) module provides procedures to connect to the daemon, and to perform RPCs.  These are described below.

 -- Scheme Procedure: open-connection [FILE] [#:reserve-space? #t]
     Connect to the daemon over the Unix-domain socket at FILE.  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.

 -- Scheme Procedure: close-connection SERVER
     Close the connection to SERVER.

 -- Scheme 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.

 -- Scheme Procedure: valid-path? SERVER PATH
     Return #t when PATH is a valid store path.

 -- Scheme 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.

 -- Scheme Procedure: build-derivations SERVER DERIVATIONS
     Build DERIVATIONS (a list of <derivation> objects or derivation paths), and return when the worker is done building them. Return #t on success.

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 contain 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 derivations, 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).

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:

 -- Scheme 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] [#:leaked-env-vars #f] [#:local-build? #f]
     [#:substitutable? #t]
     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.

     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.

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.

 -- Scheme 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]
     [#: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, 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 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 Guile's REPL with new ``meta-commands'' to make it easier to deal with monadic procedures: run-in-store, and enter-store-monad.  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.

The main syntactic forms to deal with monads in general are provided by the (guix monads) module and are described below.

 -- Scheme Syntax: with-monad MONAD BODY ...
     Evaluate any >>= or return forms in BODY as being in MONAD.

 -- Scheme Syntax: return VAL
     Return a monadic value that encapsulates VAL.

 -- Scheme Syntax: >>= 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

 -- Scheme Syntax: mlet MONAD ((VAR MVAL) ...)
     BODY ...
 -- Scheme Syntax: mlet* MONAD ((VAR MVAL) ...)
     BODY ...
     Bind the variables VAR to the monadic values MVAL in BODY.  The form (VAR -> VAL) binds VAR to the ``normal'' value VAL, as per let.

     mlet* is to mlet what let* is to let (see Local Bindings (GNU Guile Reference Manual)).

 -- Scheme System: mbegin MONAD MEXP ...
     Bind MEXP and the following monadic expressions in sequence, returning the result of the last 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.

The (guix monads) module provides the state monad, which allows an additional value---the state---to be threaded through monadic procedure calls.

 -- Scheme 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.

 -- Scheme 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.

 -- Scheme 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.)

 -- Scheme 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: interned-file FILE [NAME]
     [#:recursive? #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.

     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.

 -- 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). Those 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 those 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, etc.

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 Scheme's homoiconicity---code has a direct representation as data---comes in handy for that.  But we need more than Scheme's normal quasiquote mechanism 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 in three syntactic forms: gexp, ungexp, and ungexp-splicing (or simply: #~, #$, and #$@), which are comparable respectively to quasiquote, unquote, and unquote-splicing (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 can be defined, such that these objects can also be inserted into gexps.  For example, a useful type of high-level object that can be inserted in a gexp is ``file-like objects'', which make it easy to add files to the store and 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 derivation's output directory name.

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 #$output)
            (system* (string-append #+coreutils "/bin/ln")
                     "-s"
                     (string-append #$emacs "/bin/emacs")
                     (string-append #$output "/bin/vi")))
        #:target "mips64el-linux")

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.

The syntactic form to construct gexps is summarized below.

 -- Scheme Syntax: #~EXP
 -- Scheme Syntax: (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).

     #+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.)

 -- Scheme 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]
     [#:references-graphs #f] [#:allowed-references #f]
     [#:leaked-env-vars #f]
     [#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f]
     Return a derivation NAME that runs EXP (a gexp) with GUILE-FOR-BUILD (a derivation) on SYSTEM.  When TARGET is true, it is used as the cross-compilation target triplet for packages referred to by EXP.

     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)).

     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 PACKAGE)
          (FILE-NAME PACKAGE OUTPUT)
          (FILE-NAME DERIVATION)
          (FILE-NAME DERIVATION OUTPUT)
          (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.

     The other arguments are as for derivation (see Derivations).

The local-file and plain-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* (string-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.

 -- Scheme Procedure: local-file FILE [NAME]
     [#:recursive? #t]
     Return an object representing local file FILE to add to the store; this object can be used in a gexp.  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.

     This is the declarative counterpart of the interned-file monadic procedure (see interned-file).

 -- Scheme Procedure: plain-file NAME CONTENT
     Return an object representing a text file called NAME with the given CONTENT (a string) to be added to the store.

     This is the declarative counterpart of text-file.

 -- Monadic Procedure: gexp->script NAME EXP
     Return an executable script NAME that runs EXP using GUILE with MODULES in its search 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 (string-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 (string-append "/gnu/store/...-coreutils-8.22"/bin/ls")
                 "ls")

 -- Monadic Procedure: gexp->file NAME EXP
     Return a derivation that builds a file NAME containing EXP.

     The resulting file holds references to all the dependencies of EXP or a subset thereof.

 -- 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 references COREUTILS, GREP, and SED, thereby preventing them from being garbage-collected during its lifetime.

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.

Utilities
*********

This section describes tools primarily targeted at developers and users who write new package definitions.  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...

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 disambiguation among several same-named packages or package variants is needed.

The OPTIONS may be zero or more of the following:

--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.

     Alternately, 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 packages' source derivations, rather than the packages themselves.

     For instance, guix build -S gcc returns something like /gnu/store/...-gcc-4.7.2.tar.bz2, which is GCC's source tarball.

     The returned source tarball is the result of applying any patches and code snippets specified in the package's origin (see Defining 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 all packages' source derivations, 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 all packages' source derivations, as well as all source derivations for packages' transitive inputs.  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 host's system type.

     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 allows users to build packages in a complete 32-bit environment.

--target=TRIPLET
     Cross-build for TRIPLET, which must be a valid GNU triplet, such as "mips64el-linux-gnu" (see GNU configuration triplets (GNU Configure and Build System)).

--with-source=SOURCE
     Use SOURCE as the source of the corresponding package. SOURCE must be a file name or a URL, as for guix download (see Invoking guix download).

     The ``corresponding package'' is taken to be one specified on the command line whose name matches the base of SOURCE---e.g., if SOURCE is /src/guile-2.0.10.tar.gz, the corresponding package is guile.  Likewise, the version string is inferred from SOURCE; in the previous example, it's 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-1.7.tar.gz

     As a developer, --with-source makes it easy to test release candidates:

          guix build guile --with-source=../guile-2.0.9.219-e1bb7.tar.xz

     ... 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

--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.

--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.

--log-file
     Return the build log file names for the given PACKAGE-OR-DERIVATIONs, 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)'

In addition, 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 fail, 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.

--dry-run
-n
     Do not build the derivations.

--fallback
     When substituting a pre-built binary fails, fall back to building packages locally.

--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-build-hook
     Do not attempt to offload builds via the daemon's ``build hook'' (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.

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

     By default there is no timeout.  This behavior can be restored with --timeout=0.

--verbosity=LEVEL
     Use the given verbosity level.  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.

--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.

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.

Invoking guix edit
==================

So many packages, so many source files!  The guix edit command facilitates the life of packagers by pointing their editor at the source file containing the definition of the specified packages.  For instance:

     guix edit gcc-4.8 vim

launches the program specified in the EDITOR environment variable to edit the recipe of GCC 4.8.4 and that of Vim.

If you are using Emacs, note that the Emacs user interface provides similar functionality in the ``package info'' and ``package list'' buffers created by M-x guix-search-by-name and similar commands (see Emacs Commands).

Invoking guix download
======================

When writing a package definition, developers typically need to download the package's 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.

The following option is available:

--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.

Invoking guix hash
==================

The guix hash command computes the SHA256 hash of a file. It is primarily a convenience tool for anyone contributing to the distribution: it computes the cryptographic hash of a file, which can be used in the definition of a package (see Defining Packages).

The general syntax is:

     guix hash OPTION FILE

guix hash has the following option:

--format=FMT
-f FMT
     Write the hash in the format specified by FMT.

     Supported formats: 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
     Compute the hash on FILE recursively.

     In this case, the hash is computed on an archive containing FILE, including its children if it is a directory.  Some of FILE's meta-data 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.  Meta-data such as time stamps has no impact on the hash (see Invoking guix archive).

Invoking guix import
====================

The guix import command is useful for people willing to add a package to the distribution but who'd rather do as little work as possible to get there---a legitimate demand.  The command knows of a few repositories from which it can ``import'' package meta-data.  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 meta-data, and OPTIONS specifies a package identifier and other options specific to IMPORTER.  Currently, the available ``importers'' are:

gnu
     Import meta-data 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's 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's signature.  See --key-download.

pypi
     Import meta-data from the Python Package Index (https://pypi.python.org/) (This functionality requires Guile-JSON to be installed. See Requirements.).  Information is taken from the JSON-formatted description available at pypi.python.org and usually includes all the relevant information, including package dependencies.

     The command below imports meta-data for the itsdangerous Python package:

          guix import pypi itsdangerous

cpan
     Import meta-data from MetaCPAN (https://www.metacpan.org/). Information is taken from the JSON-formatted meta-data provided through MetaCPAN's API (https://api.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 command below imports meta-data for the Acme::Boolean Perl module:

          guix import cpan Acme::Boolean

nix
     Import meta-data from a local copy of the source of the Nixpkgs distribution (http://nixos.org/nixpkgs/) (This relies on the nix-instantiate command of Nix (http://nixos.org/nix/).).  Package definitions in Nixpkgs are typically written in a mixture of Nix-language and Bash code.  This command only imports the high-level package structure that is written in the Nix language.  It normally includes all the basic fields of a package definition.

     When importing a GNU package, the synopsis and descriptions are replaced by their canonical upstream variant.

     As an example, the command below imports the package definition of LibreOffice (more precisely, it imports the definition of the package bound to the libreoffice top-level attribute):

          guix import nix ~/path/to/nixpkgs libreoffice

hackage
     Import meta-data from 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 the standard input.

     --no-test-dependencies
     -t
          Do not include dependencies required by the test suites only.

     --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.

     The command below imports meta-data 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 a hyphen and a version number as in the following example:

          guix import hackage mtl-2.1.3.1

elpa
     Import meta-data 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 (http://elpa.gnu.org/packages), selected by the gnu identifier.  This is the default.

            - MELPA-Stable (http://stable.melpa.org/packages), selected by the melpa-stable identifier.

            - MELPA (http://melpa.org/packages), selected by the melpa identifier.

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 developers of the GNU software distribution.  By default, it 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

It does so by browsing each package's FTP directory and determining the highest version number of the source tarballs therein (Currently, this only works for GNU packages.).

When passed --update, it modifies distribution source files to update the version numbers and source tarball hashes of those packages' recipes (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 gpg, and finally computing its hash.  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 it's successful, the key is added to the user's keyring; otherwise, guix refresh reports an error.

The following options are supported:

--update
-u
     Update distribution source files (package recipes) in place. See Defining Packages, for more information on package definitions.

--select=[SUBSET]
-s SUBSET
     Select all the packages in SUBSET, one of core or non-core.

     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.

In addition, guix refresh can be passed one or more package names, as in this example:

     guix refresh -u emacs idutils gcc-4.8.4

The command above specifically updates the emacs and idutils packages.  The --select option would have no effect in this case.

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.

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 geiser-0.4 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.

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.

--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.

Invoking guix lint
==================

The guix lint 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
     Probe home-page and source URLs and report those that are invalid.

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:

--checkers
-c
     Only enable the checkers specified in a comma-separated list using the names returned by --list-checkers.

--list-checkers
-l
     List and describe all the available checkers that will be run on packages and exit.

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).  These are the typical issues that guix size can highlight.

The command can be passed a package specification 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/...-coreutils-8.23          70.0    13.9  19.8%
     /gnu/store/...-gmp-6.0.0a              55.3     2.5   3.6%
     /gnu/store/...-acl-2.2.52              53.7     0.5   0.7%
     /gnu/store/...-attr-2.4.46             53.2     0.3   0.5%
     /gnu/store/...-gcc-4.8.4-lib           52.9    15.7  22.4%
     /gnu/store/...-glibc-2.21              37.2    37.2  53.1%

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 3 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 item's size to the space occupied by all the items listed here.

In this example, we see that the closure of Coreutils weighs in at 70 MiB, half of which is taken by libc.  (That libc represents a large fraction of the closure is not a problem per se because it is always available on the system anyway.)

When the package passed to guix size is available in the store, 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 package is not in the store, guix size reports information based on information about the available substitutes (see Substitutes).  This allows it to profile disk usage of store items that are not even on disk, only available remotely.

The available options are:

--map-file=FILE
     Write to FILE a graphical map of disk usage as a PNG 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 (http://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.

Invoking guix environment
=========================

The purpose of guix environment is to assist hackers in creating reproducible development environments without polluting their package profile.  The guix environment tool takes one or more packages, builds all of the necessary inputs, and creates a shell environment to use them.

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 specified packages are not built yet, guix environment automatically builds them.  The new shell's environment 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.).

guix environment defines the GUIX_ENVIRONMENT variable in the shell it spaws.  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

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.  The --exec option can be used to specify the command to run instead.

     guix environment guile --exec=make

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 2.7 and NumPy:

     guix environment --ad-hoc python2-numpy python-2.7 -E python

The available options are summarized below.

--expression=EXPR
-e EXPR
     Create an environment for the package 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.

--load=FILE
-l FILE
     Create an environment for the package 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]

--exec=COMMAND

-E COMMAND
     Execute COMMAND in the new environment.

--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 -E 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).

--pure
     Unset existing environment variables when building the new environment. This has the effect of creating an environment in which search paths only contain package inputs.

--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.

It also supports all of the common build options that guix build supports (see common build options).

Invoking guix publish
=====================

The purpose of guix publish is to enable users to easily share their store with others, which 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 Hydra, the software behind the hydra.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 system's signing key, 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 general syntax is:

     guix publish OPTIONS...

Running guix publish without any additional arguments will spawn an HTTP server on port 8080:

     guix publish

Once a publishing server has been authorized (see Invoking guix archive), the daemon may download substitutes from it:

     guix-daemon --substitute-urls=http://example.org:8080

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.

--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.

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 (http://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).  To distinguish between the two, we refer to the standalone distribution as the Guix System Distribution, or GuixSD.

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 (http://www.gnu.org/software/guix/package-list.html) or by running guix package (see Invoking guix package):

     guix package --list-available

Our goal has been 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 VFP3D16 coprocessor, using the EABI hard-float ABI, and Linux-Libre kernel.

mips64el-linux
     little-endian 64-bit MIPS processors, specifically the Loongson series, n32 application binary interface (ABI), and Linux-Libre kernel.

GuixSD itself is currently only available on i686 and x86_64.

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.

System Installation
===================

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

You're 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 Help (Info: An Introduction).  Hit l afterwards to come back here.

Limitations
-----------

As of version VERSION, the Guix System Distribution (GuixSD) is not production-ready.  It may contain bugs and lack important features.  Thus, if you are looking for a stable production system that respects your freedom as a computer user, a good solution at this point is to consider one of more established GNU/Linux distributions (http://www.gnu.org/distros/free-distros.html).  We hope you can soon switch to the GuixSD without fear, of course.  In the meantime, you can also keep using your distribution and try out the package manager on top of it (see Installation).

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

  * The installation process does not include a graphical user interface and requires familiarity with GNU/Linux (see the following subsections to get a feel of what that means.)

  * The system does not yet provide GNOME and KDE; it provides Xfce, though, if graphical desktop environments are your thing.

  * Support for the Logical Volume Manager (LVM) is missing.

  * Few system services are currently supported out-of-the-box (see Services).

  * On the order of 1,900 packages are available, which means that you may occasionally find that a useful package is missing.

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

USB Stick Installation
----------------------

An installation image for USB sticks can be downloaded from ftp://alpha.gnu.org/gnu/guix/guixsd-usb-install-VERSION.SYSTEM.xz, where SYSTEM is 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.

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

To copy the image to a USB stick, follow these steps:

 1. Decompress the image using the xz command:

          xz -d guixsd-usb-install-VERSION.SYSTEM.xz

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

          dd if=guixsd-usb-install-VERSION.x86_64 of=/dev/sdX

     Access to /dev/sdX usually requires root privileges.

Once this is done, you should be able to reboot the system and boot from the USB stick.  The latter usually requires you to get in the BIOS' boot menu, where you can choose to boot from the USB stick.

Preparing for Installation
--------------------------

Once you have successfully booted the image on the USB stick, you should end up with a root prompt.  Several console TTYs are configured and can be used to run commands as root.  TTY2 shows this documentation, browsable using the Info reader commands (see Help (Info: An Introduction)).

To install the system, you would:

 1. Configure the network, by running ifconfig eno1 up && dhclient eno1 (to get an automatically assigned IP address from the wired network interface controller (The name eno1 is for the first on-board Ethernet controller.  The interface name for an Ethernet controller that is in the first slot of the first PCI bus, for instance, would be enp1s0.  Use ifconfig -a to list all the available network interfaces.)), or using the ifconfig command.

     The system automatically loads drivers for your network interface controllers.

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

 2. Unless this has already been done, you must partition and format the target partitions.

     Preferably, assign partitions 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.

     The installation image includes Parted (see Overview (GNU Parted User Manual)), fdisk, Cryptsetup/LUKS for disk encryption, and e2fsprogs, the suite of tools to manipulate ext2/ext3/ext4 file systems.

 3. Once that is done, mount the target root partition under /mnt.

 4. Lastly, run deco start cow-store /mnt.

     This will make /gnu/store copy-on-write, such that packages added to it during the installation phase will be written to the target disk rather than kept in memory.

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

With the target partitions ready, you now have to edit a file and provide the declaration of the operating system to be installed.  To that end, the installation system comes with two text editors: GNU nano (see GNU nano Manual), and GNU Zile, an Emacs clone. It is better to store that file on the target root file system, say, as /mnt/etc/config.scm.

See Using the Configuration System, for examples of operating system configurations.  These examples are available under /etc/configuration in the installation image, so you can copy them and use them as a starting point for your own configuration.

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 will copy all the necessary files, and install GRUB on /dev/sdX, unless you pass the --no-grub 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.  Cross fingers, and join us on #guix on the Freenode IRC network or on guix-devel@gnu.org to share your experience---good or not so good.

Building the Installation Image
-------------------------------

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

     guix system disk-image --image-size=850MiB gnu/system/install.scm

See Invoking guix system, for more information.  See gnu/system/install.scm in the source tree for more information about the installation image.

System Configuration
====================

The Guix System Distribution 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 one 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 system's own tools.

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 system services, the default Linux-Libre kernel, initial RAM disk, and boot loader looks like this:

          [file os-config-bare-bones.texi not included]

This example should be self-describing.  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.

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 GNU Zile lightweight text editor, find, grep, etc.  The example above adds Emacs to those, taken from the (gnu packages emacs) module (see Package Modules).

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 lshd secure shell daemon listening on port 2222, and allowing remote root logins (see Invoking lshd (GNU lsh Manual)).  Under the hood, lsh-service arranges so that lshd is started with the right command-line options, possibly with supporting configuration files generated as needed (see Defining Services).  See operating-system Reference, for details about the available operating-system fields.

The configuration for a typical ``desktop'' usage, with the X11 display server, a desktop environment, network management, an SSH server, and more, would look like this:

          [file os-config-desktop.texi not included]

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.

Assuming the above snippet 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).  The normal way to change the system's configuration is by updating this file and re-running the guix system command.

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.

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 supported.  In the future, it will be possible to use the GNU Hurd.).

     bootloader
          The system bootloader configuration object.  See GRUB Configuration.

     initrd (default: base-initrd)
          A two-argument monadic procedure that returns an initial RAM disk for the Linux kernel.  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-based WiFi devices (Linux-libre module ath9k.)

     host-name
          The host name.

     hosts-file
          A file-like object (see file-like objects) for use as /etc/hosts (see Host Names (The GNU C Library Reference Manual)).  The default is a file with entries for localhost and 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 strings identifying devices to be used for ``swap space'' (see Memory Concepts (The GNU C Library Reference Manual)). For example, '("/dev/sda3").

     users (default: %base-user-accounts)
     groups (default: %BASE-GROUPS)
          List of user accounts and groups.  See User Accounts.

     skeletons (default: (default-skeletons))
          A monadic list of pairs of target file name and files.  These are the files that will be used as skeletons as new accounts are created.

          For instance, a valid value may look like this:

               (mlet %store-monad ((bashrc (text-file "bashrc" "\
                    export PATH=$HOME/.guix-profile/bin")))
                 (return `((".bashrc" ,bashrc))))

     issue (default: %DEFAULT-ISSUE)
          A string denoting the contents of the /etc/issue file, which is what displayed when users log in on a text console.

     packages (default: %BASE-PACKAGES)
          The set of packages installed in the global profile, which is accessible at /run/current-system/profile.

          The default set includes core utilities, but it is good practice to install non-core utilities in user profiles (see Invoking guix package).

     timezone
          A timezone identifying string---e.g., "Europe/Paris".

     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.

     name-service-switch (default: %DEFAULT-NSS)
          Configuration of libc's name service switch (NSS)---a <name-service-switch> object.  See Name Service Switch, for details.

     services (default: %BASE-SERVICES)
          A list of monadic values denoting system services.  See Services.

     pam-services (default: (base-pam-services))
          Linux pluggable authentication module (PAM) services.

     setuid-programs (default: %SETUID-PROGRAMS)
          List of string-valued G-expressions denoting setuid programs. See Setuid Programs.

     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.

File Systems
------------

The list of file systems to be mounted is specified in the file-systems field of the operating system's 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.  By default it is the name of a node under /dev, but its meaning depends on the title field described below.

     title (default: 'device)
          This is a symbol that specifies how the device field is to be interpreted.

          When it is the symbol device, then the device field is interpreted as a file name; when it is label, then device is interpreted as a partition label name; when it is uuid, device is interpreted as a partition unique identifier (UUID).

          The label and uuid options offer a way to refer to disk partitions without having to hard-code their actual device name.

          However, when a file system's source is a mapped device (see Mapped Devices), its device field must refer to the mapped device name---e.g., /dev/mapper/root-partition---and consequently title must be set to 'device.  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), and no-exec (disallow program execution.)

     options (default: #f)
          This is either #f, or a string denoting mount options.

     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 needs to be checked for errors before being mounted.

     create-mount-point? (default: #f)
          When true, the mount point is created if it does not exist yet.

The (gnu system file-systems) exports the following useful variables.

 -- Scheme Variable: %base-file-systems
     These are essential file systems that are required on normal systems, such as %DEVTMPFS-FILE-SYSTEM and %IMMUTABLE-STORE (see below.)  Operating system declarations should always contain at least these.

 -- Scheme Variable: %devtmpfs-file-system
     The devtmpfs file system to be mounted on /dev.  This is a requirement for udev (see udev-service).

 -- Scheme 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.

 -- Scheme 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)).

 -- Scheme 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.''

 -- Scheme 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.

 -- Scheme 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.

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, 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.

Mapped devices are declared using the mapped-device form:

     (mapped-device
       (source "/dev/sda3")
       (target "home")
       (type luks-device-mapping))

This example specifies a mapping from /dev/sda3 to /dev/mapper/home using LUKS---the Linux Unified Key Setup (http://code.google.com/p/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).  The mapped-device form is detailed below.

 -- Data Type: mapped-device
     Objects of this type represent device mappings that will be made when the system boots up.

     source
          This string specifies the name of the block device to be mapped, such as "/dev/sda3".

     target
          This string specifies the name of the mapping to be established.  For example, specifying "my-partition" will lead to the creation of the "/dev/mapper/my-partition" device.

     type
          This must be a mapped-device-kind object, which specifies how SOURCE is mapped to TARGET.

 -- Scheme Variable: luks-device-mapping
     This defines LUKS block device encryption using the cryptsetup command, from the same-named package.  This relies on the dm-crypt Linux kernel module.

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")
       (home-directory "/home/alice"))

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's owner full name.

     home-directory
          This is the name of the home directory for the account.

     shell (default: Bash)
          This is a G-expression denoting the file name of a program to be used as the shell (see G-Expressions).

     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 have a preset password for an account, then this field must contain the encrypted password, as a string. See crypt (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 group's name.

     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 group's password.

For convenience, a variable lists all the basic user groups one may expect:

 -- Scheme 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''.

 -- Scheme 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.

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.CHARSET---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).

That locale must be among the locale definitions that are known to the system---and these are specified in the locale-definitions slot of operating-system.  The default value includes locale definition for some widely used locales, but not for all the available locales, in order to save space.

If the locale specified in the locale field is not among the definitions listed in locale-definitions, guix system raises an error.  In that case, you should add the locale definition to the locale-definitions field.  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 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 (http://www.iana.org/assignments/character-sets).

 -- Scheme Variable: %default-locale-definitions
     An arbitrary list of commonly used locales, used as the default value of the locale-definitions field of operating-system declarations.

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.

Services are managed by GNU dmd (see Introduction (GNU dmd Manual)).  On a running system, the deco command allows you to list the available services, show their status, start and stop them, or do other specific operations (see Jump Start (GNU dmd Manual)).  For example:

     # deco status dmd

The above command, run as root, lists the currently defined services.  The deco doc command shows a synopsis of the given service:

     # deco doc nscd
     Run libc's name service cache daemon (nscd).

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:

     # deco stop nscd
     Service nscd has been stopped.
     # deco restart xorg-server
     Service xorg-server has been stopped.
     Service xorg-server has been started.

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.

 -- Scheme Variable: %base-services
     This variable contains a list of basic services (Technically, this is a list of monadic services.  See The Store Monad.) one would expect from the system: a login service (mingetty) on each tty, syslogd, libc's 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:

          (cons* (avahi-service) (lsh-service) %base-services)

 -- Monadic Procedure: host-name-service NAME
     Return a service that sets the host name to NAME.

 -- Monadic Procedure: mingetty-service TTY [#:motd]
     [#:auto-login #f] [#:login-program] [#:login-pause? #f]
     [#:allow-empty-passwords? #f]
     Return a service to run mingetty on TTY.

     When ALLOW-EMPTY-PASSWORDS? is true, allow empty log-in password.  When AUTO-LOGIN is true, it must be a user name under which to log-in automatically.  LOGIN-PAUSE? can be set to #t in conjunction with AUTO-LOGIN, in which case the user will have to press a key before the login shell is launched.

     When true, LOGIN-PROGRAM is a gexp or a monadic gexp denoting the name of the log-in program (the default is the login program from the Shadow tool suite.)

     MOTD is a monadic value containing a text file to use as the ``message of the day''.

 -- Monadic Procedure: nscd-service [CONFIG] [#:glibc glibc]
     [#:name-services '()]
     Return a service that runs libc's name service cache daemon (nscd) with the given CONFIG---an <nscd-configuration> object. Optionally, #:name-services is a list of packages that provide name service switch (NSS) modules needed by nscd.  See Name Service Switch, for an example.

 -- Scheme Variable: %nscd-default-configuration
     This is the default <nscd-configuration> value (see below) used by nscd-service.  This uses the caches defined by %NSCD-DEFAULT-CACHES; see below.

 -- Data Type: nscd-configuration
     This is the type representing the name service cache daemon (nscd) configuration.

     log-file (default: "/var/log/nscd.log")
          Name of nscd's 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 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.

 -- Scheme 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.

 -- Monadic Procedure: syslog-service [#:config-file #f]
     Return a service that runs syslogd.  If configuration file name CONFIG-FILE is not specified, use some reasonable default settings.

 -- Monadic Procedure: guix-service [#:guix guix]
     [#:builder-group "guixbuild"] [#:build-accounts 10]
     [#:authorize-hydra-key? #t] [#:use-substitutes? #t]
     [#:extra-options '()]
     Return a service that runs the build daemon from GUIX, and has BUILD-ACCOUNTS user accounts available under BUILDER-GROUP.

     When AUTHORIZE-HYDRA-KEY? is true, the hydra.gnu.org public key provided by GUIX is authorized upon activation, meaning that substitutes from hydra.gnu.org are used by default.

     If USE-SUBSTITUTES? is false, the daemon is run with --no-substitutes (see --no-substitutes).

     Finally, EXTRA-OPTIONS is a list of additional command-line options passed to guix-daemon.

 -- Monadic Procedure: udev-service [#:udev udev]
     Run UDEV, which populates the /dev directory dynamically.

 -- Monadic Procedure: console-keymap-service FILE
     Return a service to load console keymap from FILE using loadkeys command.

Networking Services
...................

The (gnu services networking) module provides services to configure the network interface.

 -- Monadic Procedure: dhcp-client-service [#:dhcp ISC-DHCP]
     Return a service that runs DHCP, a Dynamic Host Configuration Protocol (DHCP) client, on all the non-loopback network interfaces.

 -- Monadic Procedure: static-networking-service INTERFACE IP
     [#:gateway #f] [#:name-services '()]
     Return a service that starts INTERFACE with address IP.  If GATEWAY is true, it must be a string specifying the default network gateway.

 -- Monadic Procedure: wicd-service [#:wicd WICD]
     Return a service that runs Wicd (https://launchpad.net/wicd), a network manager that aims to simplify wired and wireless networking.

 -- Monadic Procedure: ntp-service [#:ntp NTP]
     [#:name-service %NTP-SERVERS]
     Return a service that runs the daemon from NTP, the Network Time Protocol package (http://www.ntp.org).  The daemon will keep the system clock synchronized with that of SERVERS.

 -- Scheme Variable: %ntp-servers
     List of host names used as the default NTP servers.

 -- Monadic Procedure: tor-service [#:tor tor]
     Return a service to run the Tor (https://torproject.org) daemon.

     The daemon runs with the default settings (in particular the default exit policy) as the tor unprivileged user.

 -- Monadic Procedure: bitlbee-service [#:bitlbee bitlbee]
     [#:interface "127.0.0.1"] [#:port 6667]
     [#:extra-settings ""]
     Return a service that runs BitlBee (http://bitlbee.org), a daemon that acts as a gateway between IRC and chat networks.

     The daemon will listen to the interface corresponding to the IP address specified in INTERFACE, on PORT.  127.0.0.1 means that only local clients can connect, whereas 0.0.0.0 means that connections can come from any networking interface.

     In addition, EXTRA-SETTINGS specifies a string to append to the configuration file.

Furthermore, (gnu services ssh) provides the following service.

 -- Monadic Procedure: lsh-service [#:host-key "/etc/lsh/host-key"]
     [#:daemonic? #t] [#:interfaces '()] [#:port-number 22]
     [#:allow-empty-passwords? #f] [#:root-login? #f]
     [#:syslog-output? #t] [#:x11-forwarding? #t]
     [#:tcp/ip-forwarding? #t] [#:password-authentication? #t]
     [#:public-key-authentication? #t] [#:initialize? #t]
     Run the lshd program from LSH to listen on port PORT-NUMBER. HOST-KEY must designate a file containing the host key, and readable only by root.

     When DAEMONIC? is true, lshd will detach from the controlling terminal and log its output to syslogd, unless one sets SYSLOG-OUTPUT? to false.  Obviously, it also makes lsh-service depend on existence of syslogd service.  When PID-FILE? is true, lshd writes its PID to the file called PID-FILE.

     When INITIALIZE? is true, automatically create the seed and host key upon service activation if they do not exist yet.  This may take long and require interaction.

     When INITIALIZE? is false, 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)).

     When INTERFACES is empty, lshd listens for connections on all the network interfaces; otherwise, INTERFACES must be a list of host names or addresses.

     ALLOW-EMPTY-PASSWORDS? specifies whether to accept log-ins with empty passwords, and ROOT-LOGIN? specifies whether to accept log-ins as root.

     The other options should be self-descriptive.

 -- Scheme Variable: %facebook-host-aliases
     This variable contains a string for use in /etc/hosts (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 variable is typically used in the hosts-file field of an operating-system declaration (see /etc/hosts):

          (use-modules (gnu) (guix))

          (operating-system
            (host-name "mymachine")
            ;; ...
            (hosts-file
              ;; Create a /etc/hosts file with aliases for "localhost"
              ;; and "mymachine", as well as for Facebook servers.
              (plain-file "hosts"
                          (string-append (local-host-aliases host-name)
                                         %facebook-host-aliases))))

     This mechanism can prevent programs running locally, such as Web browsers, from accessing Facebook.

The (gnu services avahi) provides the following definition.

 -- Monadic Procedure: avahi-service [#:avahi AVAHI]
     [#:host-name #f] [#:publish? #t] [#:ipv4? #t]
     [#:ipv6? #t] [#:wide-area? #f]
     [#:domains-to-browse '()]
     Return a service that runs avahi-daemon, a system-wide mDNS/DNS-SD responder that allows for service discovery and "zero-configuration" host name lookups (see http://avahi.org/).

     If HOST-NAME is different from #f, use that as the host name to publish for this machine; otherwise, use the machine's actual host name.

     When PUBLISH? is true, publishing of host names and services is allowed; in particular, avahi-daemon will publish the machine's host name and IP address via mDNS on the local network.

     When WIDE-AREA? is true, DNS-SD over unicast DNS is enabled.

     Boolean values IPV4? and IPV6? determine whether to use IPv4/IPv6 sockets.

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, currently SLiM.

 -- Monadic Procedure: slim-service [#:allow-empty-passwords? #f]
     [#:auto-login? #f] [#:default-user ""] [#:startx]
     [#:theme %DEFAULT-SLIM-THEME]
     [#:theme-name %DEFAULT-SLIM-THEME-NAME]
     Return a service that spawns the SLiM graphical login manager, which in turn starts the X display server with STARTX, a command as returned by xorg-start-command.

     SLiM automatically looks for session types described by the .desktop files in /run/current-system/profile/share/xsessions and allows users to choose a session from the log-in screen using F1.  Packages such as XFCE, SAWFISH, and RATPOISON 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.

     When ALLOW-EMPTY-PASSWORDS? is true, allow logins with an empty password.  When AUTO-LOGIN? is true, log in automatically as DEFAULT-USER.

     If THEME is #f, the use the default log-in theme; otherwise THEME must be a gexp denoting the name of a directory containing the theme to use.  In that case, THEME-NAME specifies the name of the theme.

 -- Scheme Variable: %default-theme
 -- Scheme Variable: %default-theme-name
     The G-Expression denoting the default SLiM theme and its name.

 -- Monadic Procedure: xorg-start-command [#:guile]
     [#:configuration-file #f] [#:xorg-server XORG-SERVER]
     Return a derivation that builds a GUILE script to start the X server from XORG-SERVER.  CONFIGURATION-FILE is the server configuration file or a derivation that builds it; when omitted, the result of xorg-configuration-file is used.

     Usually the X server is started by a login manager.

 -- Monadic Procedure: xorg-configuration-file
     [#:drivers '()] [#:resolutions '()] [#:extra-config '()]
     Return a configuration file for the Xorg server containing search paths for all the common drivers.

     DRIVERS 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\").

     Likewise, 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)).

     Last, EXTRA-CONFIG is a list of strings or objects appended to the text-file* argument list.  It is used to pass extra text to be added verbatim to the configuration file.

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.

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:

 -- Scheme Variable: %desktop-services
     This is a list of services that builds upon %BASE-SERVICES and adds or adjust services for a typical ``desktop'' setup.

     In particular, it adds a graphical login manager (see slim-service), a network management tool (see wicd-service), energy and color management services, an NTP client (see Networking Services), the Avahi daemon, and has the name service switch service configured to be able to use nss-mdns (see mDNS).

The %DESKTOP-SERVICES variable can be used as the services field of an operating-system declaration (see services).

The actual service definitions provided by (gnu services desktop) are described below.

 -- Monadic Procedure: dbus-service SERVICES
     [#:dbus DBUS]
     Return a service that runs the ``system bus'', using DBUS, with support for SERVICES.

     D-Bus (http://dbus.freedesktop.org/) is an inter-process communication facility.  Its system bus is used to allow system services to communicate and be notified of system-wide events.

     SERVICES must be a 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).

 -- Monadic Procedure: upower-service [#:upower UPOWER]
     [#:watts-up-pro? #f]
     [#:poll-batteries? #t]
     [#:ignore-lid? #f]
     [#:use-percentage-for-policy? #f]
     [#:percentage-low 10]
     [#:percentage-critical 3]
     [#:percentage-action 2]
     [#:time-low 1200]
     [#:time-critical 300]
     [#:time-action 120]
     [#:critical-power-action 'hybrid-sleep]
     Return a service that runs upowerd (http://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.

 -- Monadic Procedure: colord-service [#:colord COLORD]
     Return a 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 (http://www.freedesktop.org/software/colord/) for more information.

Database Services
.................

The (gnu services databases) module provides the following service.

 -- Monadic Procedure: postgresql-service [#:postgresql postgresql]
     [#:config-file] [#:data-directory ``/var/lib/postgresql/data'']
     Return a service that runs POSTGRESQL, the PostgreSQL database server.

     The PostgreSQL daemon loads its runtime configuration from CONFIG-FILE and stores the database cluster in DATA-DIRECTORY.

Various Services
................

The (gnu services lirc) module provides the following service.

 -- Monadic Procedure: lirc-service [#:lirc lirc]
     [#:device #f] [#:driver #f] [#:config-file #f]
     [#:extra-options '()]
     Return a service that runs LIRC (http://www.lirc.org), a daemon that decodes infrared signals from remote controls.

     Optionally, DEVICE, DRIVER and CONFIG-FILE (configuration file name) may be specified.  See lircd manual for details.

     Finally, EXTRA-OPTIONS is a list of additional command-line options passed to lircd.

Setuid Programs
---------------

Some programs need to run with ``root'' privileges, even when they are launched by unprivileged users.  A notorious example is the passwd programs, which can users can run to change their password, and which requires write access to the /etc/passwd and /etc/shadow files---something normally restricted to root, for obvious security reasons.  To address that, these executables are setuid-root, meaning that they always run with root privileges (see How Change Persona (The GNU C Library Reference Manual), for more info about the setuid mechanisms.)

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 bit directly on files that are in the store, we let the system administrator declare which programs should be setuid root.

The setuid-programs field of an operating-system declaration contains a list of G-expressions denoting the names of programs to be setuid-root (see Using the Configuration System). For instance, the passwd program, which is part of the Shadow package, can be designated by this G-expression (see G-Expressions):

     #~(string-append #$shadow "/bin/passwd")

A default set of setuid programs is defined by the %setuid-programs variable of the (gnu system) module.

 -- Scheme Variable: %setuid-programs
     A list of G-expressions 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.

In GuixSD, this is done by adding a package that provides certificates to the packages field of the operating-system declaration (see operating-system Reference).  GuixSD 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 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.

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

The (gnu system nss) module provides bindings to the configuration file of libc's 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 (http://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")))))

Don't worry: the %mdns-host-lookup-nss variable (see below) contains this configuration, so you won't 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, nscd-service must be told where to find the nss-mdns shared library (see nscd-service).  Since the nscd service is part of %BASE-SERVICES, you may want to customize it by adding this snippet in the operating system configuration file:

     (use-modules (guix) (gnu))

     (define %my-base-services
       ;; Replace the default nscd service with one that knows
       ;; about nss-mdns.
       (map (lambda (mservice)
              ;; "Bind" the MSERVICE monadic value to inspect it.
              (mlet %store-monad ((service mservice))
                (if (member 'nscd (service-provision service))
                    (nscd-service (nscd-configuration)
                                  #:name-services (list nss-mdns))
                    mservice)))
            %base-services))

... and then refer to %MY-BASE-SERVICES instead of %BASE-SERVICES in the operating-system declaration. Lastly, this relies on the availability of the Avahi service (see avahi-service).

For convenience, the following variables provide typical NSS configurations.

 -- Scheme Variable: %default-nss
     This is the default name service switch configuration, a name-service-switch object.

 -- Scheme 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 C library's configuration file format, so please refer to the C library manual for more information (see NSS Configuration File (The GNU C Library Reference Manual)). Compared to libc's NSS configuration file format, it has the advantage not only of adding this warm parenthetic feel that we like, but also static checks: you'll 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 field of an operating-system declaration allows you to specify which initrd you would like to use.  The (gnu system linux-initrd) module provides two ways to build an initrd: the high-level base-initrd procedure, and the low-level expression->initrd procedure.

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 that has modules "foo.ko"
               ;; and "bar.ko", as well as their dependencies, in
               ;; addition to the modules available by default.
               (apply base-initrd file-systems
                      #:extra-modules '("foo" "bar")
                      rest)))

The base-initrd procedure also handles common use cases that involves using the system as a QEMU guest, or as a ``live'' system whose root file system is volatile.

 -- Monadic Procedure: base-initrd FILE-SYSTEMS
     [#:qemu-networking? #f] [#:virtio? #f] [#:volatile-root? #f]
     [#:extra-modules '()] [#:mapped-devices '()]
     Return a monadic derivation that builds a generic 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. MAPPED-DEVICES is a list of device mappings to realize before FILE-SYSTEMS are mounted (see Mapped Devices).

     When QEMU-NETWORKING? is true, set up networking with the standard QEMU parameters.  When VIRTIO? is true, load additional modules so 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.

     The initrd is automatically populated with all the kernel modules necessary for FILE-SYSTEMS and for the given options.  However, additional kernel modules can be listed in EXTRA-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.

 -- Monadic Procedure: expression->initrd EXP
     [#:guile %guile-static-stripped] [#:name "guile-initrd"]
     [#:modules '()]
     Return a derivation that builds 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.

     MODULES is a list of Guile module names to be embedded in the initrd.

GRUB Configuration
------------------

The operating system uses GNU GRUB as its boot loader (see overview of GRUB (GNU GRUB Manual)).  It is configured using grub-configuration declarations.  This data type is exported by the (gnu system grub) module, and described below.

 -- Data Type: grub-configuration
     The type of a GRUB configuration declaration.

     device
          This is a string denoting the boot device.  It must be a device name understood by the grub-install command, such as /dev/sda or (hd0) (see Invoking grub-install (GNU GRUB Manual)).

     menu-entries (default: ())
          A possibly empty list of menu-entry objects (see below), denoting entries to appear in the GRUB boot 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 current system's entry.

     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.

     theme (default: %DEFAULT-THEME)
          The grub-theme object describing the theme to use.

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:

 -- Data Type: menu-entry
     The type of an entry in the GRUB boot menu.

     label
          The label to show in the menu---e.g., "GNU".

     linux
          The Linux kernel to boot.

     linux-arguments (default: ())
          The list of extra Linux kernel command-line arguments---e.g., ("console=ttyS0").

     initrd
          A G-Expression or string denoting the file name of the initial RAM disk to use (see G-Expressions).

Themes are created using the grub-theme form, which is not documented yet.

 -- Scheme Variable: %default-theme
     This is the default GRUB theme used by the operating system, with a fancy background image displaying the GNU and Guix logos.

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 instantiate.  Currently the following values are supported:

reconfigure
     Build the operating system described in FILE, activate it, and switch to it (This action is usable only on systems already running GNU.).

     This effects all the configuration specified in FILE: user accounts, system services, global package list, setuid programs, etc.

     It also adds a GRUB menu entry for the new OS configuration, and moves entries for older configurations to a submenu---unless --no-grub is passed.

     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.

build
     Build the operating system's derivation, 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 GuixSD.  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 GRUB on the device specified in my-os-config, unless the --no-grub option was passed.

vm
     Build a virtual machine that contain the operating system declared in FILE, and return a script to run that virtual machine (VM). Arguments given to the script are passed as is to QEMU.

     The VM shares its store with the host system.

     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 the host's $HOME/tmp:

          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 host's store 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 image's size.

vm-image
disk-image
     Return a virtual machine or disk image of the operating system declared in FILE that stands alone.  Use the --image-size option to specify the size of the image.

     When using vm-image, the returned image is in qcow2 format, which the QEMU emulator can efficiently use.

     When using disk-image, 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 on it using the following command:

          # dd if=$(guix system disk-image my-os.scm) of=/dev/sdc

OPTIONS can contain any of the common build options provided by guix build (see Invoking guix build).  In addition, OPTIONS can contain one of the following:

--system=SYSTEM
-s SYSTEM
     Attempt to build for SYSTEM instead of the host's system type. This works as per guix build (see Invoking guix build).

--image-size=SIZE
     For the vm-image and disk-image actions, 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)).

--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 program's state.  See Debug Commands (GNU Guile Reference Manual), for a list of available debugging commands.

Note that all the actions above, except build and init, rely on KVM support in the Linux-Libre kernel.  Specifically, the machine should have 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 daemon's build users.

Defining Services
-----------------

The (gnu services ...) modules define several procedures that allow users to declare the operating system's services (see Using the Configuration System).  These procedures are monadic procedures---i.e., procedures that return a monadic value in the store monad (see The Store Monad).  For examples of such procedures, see Services.

The monadic value returned by those procedures is a service definition---a structure as returned by the service form. Service definitions specifies the inputs the service depends on, and an expression to start and stop the service.  Behind the scenes, service definitions are ``translated'' into the form suitable for the configuration file of dmd, the init system (see Services (GNU dmd Manual)).

As an example, here is what the nscd-service procedure looks like:

     (define (nscd-service)
       (with-monad %store-monad
         (return (service
                  (documentation "Run libc's name service cache daemon.")
                  (provision '(nscd))
                  (activate #~(begin
                                (use-modules (guix build utils))
                                (mkdir-p "/var/run/nscd")))
                  (start #~(make-forkexec-constructor
                            (string-append #$glibc "/sbin/nscd")
                            "-f" "/dev/null" "--foreground"))
                  (stop #~(make-kill-destructor))
                  (respawn? #f)))))

The activate, start, and stop fields are G-expressions (see G-Expressions).  The activate field contains a script to run at ``activation'' time; it makes sure that the /var/run/nscd directory exists before nscd is started.

The start and stop fields refer to dmd's facilities to start and stop processes (see Service De- and Constructors (GNU dmd Manual)).  The provision field specifies the name under which this service is known to dmd, and documentation specifies on-line documentation.  Thus, the commands deco start ncsd, deco stop nscd, and deco doc nscd will do what you would expect (see Invoking deco (GNU dmd Manual)).

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.

The problem with debugging information is that is 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 package -i 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.

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 those packages whose definition explicitly declares a debug output.  This may be changed to opt-out in the future, if our build farm servers can handle the load.  To check whether a package has a debug output, use guix package --list-available (see Invoking guix package).

Security Updates
================

     As of version VERSION, the feature described in this section is experimental.

Occasionally, important security vulnerabilities are discovered in core software packages and must be patched.  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 that, 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 that is installed will automatically be ``rewritten'' to refer to BASH-FIXED instead of BASH.  This grafting process takes time proportional to the size of the package, but expect less than a minute for an ``average'' package on a recent machine.

Currently, the graft and the package it replaces (BASH-FIXED and BASH in the example above) must have the exact same name and version fields.  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.

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 package -i 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.).  These package definitions will not be visible by default.  Thus, users can invoke commands such as guix package and guix build have to be used with the -e option so that they know where to find the package.  Better yet, they can use the -L option of these commands to make those modules visible (see --load-path), or define the GUIX_PACKAGE_PATH environment variable.  This environment variable makes it easy to extend or customize the distribution and is honored by all the user interfaces.

 -- Environment Variable: GUIX_PACKAGE_PATH
     This is a colon-separated list of directories to search for package modules.  Directories listed in this variable take precedence over the distribution's own modules.

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.

Packaging Guidelines
====================

The GNU distribution is nascent and may well lack some of your favorite packages.  This section describes how you can help make the distribution grow.  See Contributing, for additional information on how you can help.

Free software packages are usually distributed in the form of source code tarballs---typically tar.gz files that contain all the source files.  Adding a package to the distribution means essentially two things: adding a recipe that describes how to build the package, including a list of other packages required to build it, and adding package meta-data along with that recipe, such as a description and licensing information.

In Guix all this information is embodied in package definitions. Package definitions provide a high-level view of the package.  They are written using the syntax of the Scheme programming language; in fact, for each package we define a variable bound to the package definition, and export that variable from a module (see Package Modules). However, in-depth Scheme knowledge is not a prerequisite for creating packages.  For more information on package definitions, see Defining Packages.

Once a package definition is in place, stored in a file in the Guix source tree, it can be tested using the guix build command (see Invoking guix build).  For example, assuming the new package is called gnew, you may run this command from the Guix build tree (see Running Guix Before It Is Installed):

     ./pre-inst-env guix build gnew --keep-failed

Using --keep-failed makes it easier to debug build failures since it provides access to the failed build tree.  Another useful command-line option when debugging is --log-file, to access the build log.

If the package is unknown to the guix command, it may be that the source file contains a syntax error, or lacks a define-public clause to export the package variable.  To figure it out, you may load the module from Guile to get more information about the actual error:

     ./pre-inst-env guile -c '(use-modules (gnu packages gnew))'

Once your package builds correctly, please send us a patch (see Contributing).  Well, if you need help, we will be happy to help you too.  Once the patch is committed in the Guix repository, the new package automatically gets built on the supported platforms by our continuous integration system (http://hydra.gnu.org/jobset/gnu/master).

Users can obtain the new package definition simply by running guix pull (see Invoking guix pull).  When hydra.gnu.org is done building the package, installing the package automatically downloads binaries from there (see Substitutes).  The only place where human intervention is needed is to review and apply the patch.

Software Freedom
----------------

The GNU operating system has been developed so that users can have freedom in their computing.  GNU is free software, meaning that users have the four essential freedoms (http://www.gnu.org/philosophy/free-sw.html): to run the program, to study and change the program in source code form, to redistribute exact copies, and to distribute modified versions.  Packages found in the GNU distribution provide only software that conveys these four freedoms.

In addition, the GNU distribution follow the free software distribution guidelines (http://www.gnu.org/distros/free-system-distribution-guidelines.html).  Among other things, these guidelines reject non-free firmware, recommendations of non-free software, and discuss ways to deal with trademarks and patents.

Some packages contain a small and optional subset that violates the above guidelines, for instance because this subset is itself non-free code.  When that happens, the offending items are removed with appropriate patches or code snippets in the package definition's origin form (see Defining Packages).  That way, guix build --source returns the ``freed'' source rather than the unmodified upstream source.

Package Naming
--------------

A package has actually two names associated with it: First, there is the name of the Scheme variable, the one following define-public.  By this name, the package can be made known in the Scheme code, for instance as input to another package.  Second, there is the string in the name field of a package definition.  This name is used by package management commands such as guix package and guix build.

Both are usually the same and correspond to the lowercase conversion of the project name chosen upstream, with underscores replaced with hyphens.  For instance, GNUnet is available as gnunet, and SDL_net as sdl-net.

We do not add lib prefixes for library packages, unless these are already part of the official project name.  But see Python Modules and Perl Modules for special rules concerning modules for the Python and Perl languages.

Font package names are handled differently, see Fonts.

Version Numbers
---------------

We usually package only the latest version of a given free software project.  But sometimes, for instance for incompatible library versions, two (or more) versions of the same package are needed.  These require different Scheme variable names.  We use the name as defined in Package Naming for the most recent version; previous versions use the same name, suffixed by - and the smallest prefix of the version number that may distinguish the two versions.

The name inside the package definition is the same for all versions of a package and does not contain any version number.

For instance, the versions 2.24.20 and 3.9.12 of GTK+ may be packaged as follows:

     (define-public gtk+
       (package
        (name "gtk+")
        (version "3.9.12")
        ...))
     (define-public gtk+-2
       (package
        (name "gtk+")
        (version "2.24.20")
        ...))

If we also wanted GTK+ 3.8.2, this would be packaged as

     (define-public gtk+-3.8
       (package
        (name "gtk+")
        (version "3.8.2")
        ...))

Python Modules
--------------

We currently package Python 2 and Python 3, under the Scheme variable names python-2 and python as explained in Version Numbers. To avoid confusion and naming clashes with other programming languages, it seems desirable that the name of a package for a Python module contains the word python.

Some modules are compatible with only one version of Python, others with both. If the package Foo compiles only with Python 3, we name it python-foo; if it compiles only with Python 2, we name it python2-foo. If it is compatible with both versions, we create two packages with the corresponding names.

If a project already contains the word python, we drop this; for instance, the module python-dateutil is packaged under the names python-dateutil and python2-dateutil.

Perl Modules
------------

Perl programs standing for themselves are named as any other package, using the lowercase upstream name. For Perl packages containing a single class, we use the lowercase class name, replace all occurrences of :: by dashes and prepend the prefix perl-. So the class XML::Parser becomes perl-xml-parser. Modules containing several classes keep their lowercase upstream name and are also prepended by perl-.  Such modules tend to have the word perl somewhere in their name, which gets dropped in favor of the prefix.  For instance, libwww-perl becomes perl-libwww.

Fonts
-----

For fonts that are in general not installed by a user for typesetting purposes, or that are distributed as part of a larger software package, we rely on the general packaging rules for software; for instance, this applies to the fonts delivered as part of the X.Org system or fonts that are part of TeX Live.

To make it easier for a user to search for fonts, names for other packages containing only fonts are constructed as follows, independently of the upstream package name.

The name of a package containing only one font family starts with font-; it is followed by the foundry name and a dash - if the foundry is known, and the font family name, in which spaces are replaced by dashes (and as usual, all upper case letters are transformed to lower case). For example, the Gentium font family by SIL is packaged under the name font-sil-gentium.

For a package containing several font families, the name of the collection is used in the place of the font family name. For instance, the Liberation fonts consist of three families, Liberation Sans, Liberation Serif and Liberation Mono. These could be packaged separately under the names font-liberation-sans and so on; but as they are distributed together under a common name, we prefer to package them together as font-liberation.

In the case where several formats of the same font family or font collection are packaged separately, a short form of the format, prepended by a dash, is added to the package name.  We use -ttf for TrueType fonts, -otf for OpenType fonts and -type1 for PostScript Type 1 fonts.

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?  Note that this is a question of interest only to the curious hacker, not to the regular user, so you can shamelessly skip this section if you consider yourself a ``regular user''.

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 (more on that later).

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.  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, etc., 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 first tool that gets built with the bootstrap binaries is GNU Make, 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 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 (Guile, Binutils, GCC, libc, 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.

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, the glibc-dynamic-linker procedure in (gnu packages bootstrap) must be augmented to return the right file name for libc's dynamic linker on that platform; likewise, system->linux-architecture in (gnu packages linux) must be taught about the new platform.

Once these 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-system.am has rules do 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, 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
******************************

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