guix/doc/guix.texi


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								@c -*-texinfo-*-


								@c %**start of header

								@setfilename guix.info

								@documentencoding UTF-8

								@settitle GNU Guix Reference Manual

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								@include version.texi


								@copying

								Copyright @copyright{} 2012, 2013, 2014, 2015 Ludovic Courtès@*

								Copyright @copyright{} 2013, 2014 Andreas Enge@*

								Copyright @copyright{} 2013 Nikita Karetnikov@*

								Copyright @copyright{} 2015 Mathieu Lirzin@*

								Copyright @copyright{} 2014 Pierre-Antoine Rault@*

								Copyright @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''.

								@end copying


								@dircategory Package management

								@direntry

								* guix: (guix).       Guix, the functional package manager.

								* guix package: (guix)Invoking guix package

								                      Managing packages with Guix.

								* guix build: (guix)Invoking guix build

								                      Building packages with Guix.

								* guix system: (guix)Invoking guix system

								                      Managing the operating system configuration.

								@end direntry


								@dircategory Software development

								@direntry

								* guix environment: (guix)Invoking guix environment

								                      Building development environments with Guix.

								@end direntry


								@titlepage

								@title GNU Guix Reference Manual

								@subtitle Using the GNU Guix Functional Package Manager

								@author Ludovic Courtès

								@author Andreas Enge

								@author Nikita Karetnikov


								@page

								@vskip 0pt plus 1filll

								Edition @value{EDITION} @*

								@value{UPDATED} @*


								@insertcopying

								@end titlepage


								@contents


								@c *********************************************************************

								@node Top

								@top GNU Guix


								This document describes GNU Guix version @value{VERSION}, a functional

								package management tool written for the GNU system.


								@menu

								* Introduction::                What is Guix about?

								* Installation::                Installing Guix.

								* Package Management::          Package installation, upgrade, etc.

								* Programming Interface::       Using Guix in Scheme.

								* Utilities::                   Package management commands.

								* GNU Distribution::            Software for your friendly GNU system.

								* Contributing::                Your help needed!


								* Acknowledgments::             Thanks!

								* GNU Free Documentation License::  The license of this manual.

								* Concept Index::               Concepts.

								* Programming Index::           Data types, functions, and variables.


								@detailmenu

								 --- The Detailed Node Listing ---


								Installation


								* Binary Installation::         Getting Guix running in no time!

								* Requirements::                Software needed to build and run Guix.

								* Running the Test Suite::      Testing Guix.

								* Setting Up the Daemon::       Preparing the build daemon's environment.

								* Invoking guix-daemon::        Running the build daemon.


								Setting Up the Daemon


								* Build Environment Setup::     Preparing the isolated build environment.

								* Daemon Offload Setup::        Offloading builds to remote machines.


								Package Management


								* Features::                    How Guix will make your life brighter.

								* Invoking guix package::       Package installation, removal, etc.

								* Emacs Interface::             Package management from Emacs.

								* Substitutes::                 Downloading pre-built binaries.

								* Packages with Multiple Outputs::  Single source package, multiple outputs.

								* Invoking guix gc::            Running the garbage collector.

								* Invoking guix pull::          Fetching the latest Guix and distribution.

								* Invoking guix archive::       Exporting and importing store files.


								Programming Interface


								* Defining Packages::           Defining new packages.

								* Build Systems::               Specifying how packages are built.

								* The Store::                   Manipulating the package store.

								* Derivations::                 Low-level interface to package derivations.

								* The Store Monad::             Purely functional interface to the store.

								* G-Expressions::               Manipulating build expressions.


								Defining Packages


								* package Reference::           The package data type.

								* origin Reference::            The origin data type.


								Utilities


								* Invoking guix build::         Building packages from the command line.

								* Invoking guix download::      Downloading a file and printing its hash.

								* Invoking guix hash::          Computing the cryptographic hash of a file.

								* Invoking guix import::        Importing package definitions.

								* Invoking guix refresh::       Updating package definitions.

								* Invoking guix lint::          Finding errors in package definitions.

								* Invoking guix environment::   Setting up development environments.

								* Invoking guix publish::       Sharing substitutes.


								GNU Distribution


								* System Installation::         Installing the whole operating system.

								* System Configuration::        Configuring the operating system.

								* Installing Debugging Files::  Feeding the debugger.

								* Security Updates::            Deploying security fixes quickly.

								* Package Modules::             Packages from the programmer's viewpoint.

								* Packaging Guidelines::        Growing the distribution.

								* Bootstrapping::               GNU/Linux built from scratch.

								* Porting::                     Targeting another platform or kernel.


								System Configuration


								* Using the Configuration System::  Customizing your GNU system.

								* operating-system Reference::  Detail of operating-system declarations.

								* File Systems::                Configuring file system mounts.

								* Mapped Devices::              Block device extra processing.

								* User Accounts::               Specifying user accounts.

								* Locales::                     Language and cultural convention settings.

								* Services::                    Specifying system services.

								* Setuid Programs::             Programs running with root privileges.

								* X.509 Certificates::          Authenticating HTTPS servers.

								* Name Service Switch::         Configuring libc's name service switch.

								* Initial RAM Disk::            Linux-Libre bootstrapping.

								* GRUB Configuration::          Configuring the boot loader.

								* Invoking guix system::        Instantiating a system configuration.

								* Defining Services::           Adding new service definitions.


								Services


								* Base Services::               Essential system services.

								* Networking Services::         Network setup, SSH daemon, etc.

								* X Window::                    Graphical display.

								* Desktop Services::            D-Bus and desktop services.

								* Database Services::           SQL databases.

								* Various Services::            Other services.


								Packaging Guidelines


								* Software Freedom::            What may go into the distribution.

								* Package Naming::              What's in a name?

								* Version Numbers::             When the name is not enough.

								* Python Modules::              Taming the snake.

								* Perl Modules::                Little pearls.

								* Fonts::                       Fond of fonts.


								Contributing


								* Building from Git::           The latest and greatest.

								* Running Guix Before It Is Installed::  Hacker tricks.

								* The Perfect Setup::           The right tools.

								* Coding Style::                Hygiene of the contributor.

								* Submitting Patches::          Share your work.


								Coding Style


								* Programming Paradigm::        How to compose your elements.

								* Modules::                     Where to store your code?

								* Data Types and Pattern Matching::  Implementing data structures.

								* Formatting Code::             Writing conventions.


								@end detailmenu

								@end menu


								@c *********************************************************************

								@node Introduction

								@chapter Introduction


								GNU Guix@footnote{``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.


								@cindex functional package management

								The term @dfn{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 @dfn{containers}), where only their

								explicit inputs are visible.


								@cindex store

								The result of package build functions is @dfn{cached} in the file

								system, in a special directory called @dfn{the store} (@pxref{The

								Store}).  Each package is installed in a directory of its own, in the

								store---by default under @file{/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 (@pxref{Features}).


								Guix has a command-line interface, which allows users to build, install,

								upgrade, and remove packages, as well as a Scheme programming interface.


								@cindex Guix System Distribution

								@cindex GuixSD

								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@tie{}GuixSD, takes advantage of the core

								properties of Guix at the system level.  With GuixSD, users

								@emph{declare} all aspects of the operating system configuration, and

								Guix takes care of instantiating that configuration in a reproducible,

								stateless fashion.  @xref{GNU Distribution}.


								@c *********************************************************************

								@node Installation

								@chapter Installation


								GNU Guix is available for download from its website at

								@url{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,

								@pxref{System Installation}.


								@menu

								* Binary Installation::         Getting Guix running in no time!

								* Requirements::                Software needed to build and run Guix.

								* Running the Test Suite::      Testing Guix.

								* Setting Up the Daemon::       Preparing the build daemon's environment.

								* Invoking guix-daemon::        Running the build daemon.

								@end menu


								@node Binary Installation

								@section 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@tie{}tar and Xz.


								Installing goes along these lines:


								@enumerate

								@item

								Download the binary tarball from

								@indicateurl{ftp://alpha.gnu.org/gnu/guix/guix-binary-@value{VERSION}.@var{system}.tar.xz}@footnote{As

								usual, make sure to download the associated @file{.sig} file and to

								verify the authenticity of the tarball against it!}, where @var{system}

								is @code{x86_64-linux} for an @code{x86_64} machine already running the

								kernel Linux, and so on.


								@item

								As @code{root}, run:


								@example

								# cd /tmp

								# tar xf guix-binary-@value{VERSION}.@var{system}.tar.xz

								# mv var/guix /var/ && mv gnu /

								@end example


								This creates @file{/gnu/store} (@pxref{The Store}) and @file{/var/guix}.

								The latter contains a ready-to-use profile for @code{root} (see next

								step.)


								Do @emph{not} unpack the tarball on a working Guix system since that

								would overwrite its own essential files.


								@item

								Make @code{root}'s profile available under @file{~/.guix-profile}:


								@example

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

								         ~root/.guix-profile

								@end example


								@item

								Run the daemon:


								@example

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

								@end example


								@item

								Make the @command{guix} command available to other users on the machine,

								for instance with:


								@example

								# mkdir -p /usr/local/bin

								# cd /usr/local/bin

								# ln -s /var/guix/profiles/per-user/root/guix-profile/bin/guix

								@end example


								@item

								To use substitutes from @code{hydra.gnu.org} (@pxref{Substitutes}),

								authorize them:


								@example

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

								@end example

								@end enumerate


								And that's it!


								The @code{guix} package must remain available in @code{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

								@command{guix} command.


								The tarball in question can be (re)produced and verified simply by

								running the following command in the Guix source tree:


								@example

								make guix-binary.@var{system}.tar.xz

								@end example


								@node Requirements

								@section 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 @file{README} and @file{INSTALL}

								in the Guix source tree for additional details.


								GNU Guix depends on the following packages:


								@itemize

								@item @url{http://gnu.org/software/guile/, GNU Guile}, version 2.0.7 or later;

								@item @url{http://gnupg.org/, GNU libgcrypt};

								@item @url{http://www.gnu.org/software/make/, GNU Make}.

								@end itemize


								The following dependencies are optional:


								@itemize

								@item

								Installing

								@url{http://savannah.nongnu.org/projects/guile-json/, Guile-JSON} will

								allow you to use the @command{guix import pypi} command (@pxref{Invoking

								guix import}).  It is of

								interest primarily for developers and not for casual users.

								@item

								Installing @uref{http://gnutls.org/, GnuTLS-Guile} will

								allow you to access @code{https} URLs with the @command{guix download}

								command (@pxref{Invoking guix download}), the @command{guix import pypi}

								command, and the @command{guix import cpan} command.  This is primarily

								of interest to developers.  @xref{Guile Preparations, how to install the

								GnuTLS bindings for Guile,, gnutls-guile, GnuTLS-Guile}.

								@end itemize


								Unless @code{--disable-daemon} was passed to @command{configure}, the

								following packages are also needed:


								@itemize

								@item @url{http://sqlite.org, SQLite 3};

								@item @url{http://www.bzip.org, libbz2};

								@item @url{http://gcc.gnu.org, GCC's g++}, with support for the

								C++11 standard.

								@end itemize


								When a working installation of @url{http://nixos.org/nix/, the Nix package

								manager} is available, you

								can instead configure Guix with @code{--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 @command{configure} not only the

								same @code{--with-store-dir} value, but also the same

								@code{--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

								@code{--with-store-dir=/nix/store} and @code{--localstatedir=/nix/var}.

								Note that @code{--disable-daemon} is not required if

								your goal is to share the store with Nix.


								@node Running the Test Suite

								@section Running the Test Suite


								After a successful @command{configure} and @code{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:


								@example

								make check

								@end example


								Test cases can run in parallel: you can use the @code{-j} option of

								GNU@tie{}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 @email{bug-guix@@gnu.org} and attach the

								@file{test-suite.log} file.  When @file{tests/@var{something}.scm}

								fails, please also attach the @file{@var{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

								(@pxref{Requirements}) in your message.


								@node Setting Up the Daemon

								@section Setting Up the Daemon


								@cindex daemon

								Operations such as building a package or running the garbage collector

								are all performed by a specialized process, the @dfn{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

								@command{guix package} and @command{guix build} communicate with the

								daemon (@i{via} remote procedure calls) to instruct it what to do.


								The following sections explain how to prepare the build daemon's

								environment.  Also @ref{Substitutes}, for information on how to allow

								the daemon to download pre-built binaries.


								@menu

								* Build Environment Setup::     Preparing the isolated build environment.

								* Daemon Offload Setup::        Offloading builds to remote machines.

								@end menu


								@node Build Environment Setup

								@subsection Build Environment Setup


								In a standard multi-user setup, Guix and its daemon---the

								@command{guix-daemon} program---are installed by the system

								administrator; @file{/gnu/store} is owned by @code{root} and

								@command{guix-daemon} runs as @code{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.


								@cindex build users

								When @command{guix-daemon} runs as @code{root}, you may not want package

								build processes themselves to run as @code{root} too, for obvious

								security reasons.  To avoid that, a special pool of @dfn{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 @code{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 (@pxref{Introduction}).


								On a GNU/Linux system, a build user pool may be created like this (using

								Bash syntax and the @code{shadow} commands):


								@c See http://lists.gnu.org/archive/html/bug-guix/2013-01/msg00239.html

								@c for why `-G' is needed.

								@example

								# 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

								@end example


								@noindent

								The number of build users determines how many build jobs may run in

								parallel, as specified by the @option{--max-jobs} option

								(@pxref{Invoking guix-daemon, @option{--max-jobs}}).

								The @code{guix-daemon} program may then be run as @code{root} with:


								@example

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

								@end example


								@cindex chroot

								@noindent

								This way, the daemon starts build processes in a chroot, under one of

								the @code{guixbuilder} users.  On GNU/Linux, by default, the chroot

								environment contains nothing but:


								@c Keep this list in sync with libstore/build.cc! -----------------------

								@itemize

								@item

								a minimal @code{/dev} directory, created mostly independently from the

								host @code{/dev}@footnote{``Mostly'', because while the set of files

								that appear in the chroot's @code{/dev} is fixed, most of these files

								can only be created if the host has them.};


								@item

								the @code{/proc} directory; it only shows the container's processes

								since a separate PID name space is used;


								@item

								@file{/etc/passwd} with an entry for the current user and an entry for

								user @file{nobody};


								@item

								@file{/etc/group} with an entry for the user's group;


								@item

								@file{/etc/hosts} with an entry that maps @code{localhost} to

								@code{127.0.0.1};


								@item

								a writable @file{/tmp} directory.

								@end itemize


								If you are installing Guix as an unprivileged user, it is still possible

								to run @command{guix-daemon} provided you pass @code{--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

								@emph{pure} functions.


								@node Daemon Offload Setup

								@subsection Using the Offload Facility


								@cindex offloading

								@cindex build hook

								When desired, the build daemon can @dfn{offload}

								derivation builds to other machines

								running Guix, using the @code{offload} @dfn{build hook}.  When that

								feature is enabled, a list of user-specified build machines is read from

								@file{/etc/guix/machines.scm}; anytime a build is requested, for

								instance via @code{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., @file{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 @file{/etc/guix/machines.scm} file typically looks like this:


								@example

								(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")

								                        "/.ssh/id-rsa-for-guix"))))

								@end example


								@noindent

								In the example above we specify a list of two build machines, one for

								the @code{x86_64} architecture and one for the @code{mips64el}

								architecture.


								In fact, this file is---not surprisingly!---a Scheme file that is

								evaluated when the @code{offload} hook is started.  Its return value

								must be a list of @code{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 (@pxref{Introduction, Guile-Avahi,, guile-avahi, Using

								Avahi in Guile Scheme Programs}).  The @code{build-machine} data type is

								detailed below.


								@deftp {Data Type} build-machine

								This data type represents build machines the daemon may offload builds

								to.  The important fields are:


								@table @code


								@item name

								The remote machine's host name.


								@item system

								The remote machine's system type---e.g., @code{"x86_64-linux"}.


								@item user

								The user account to use when connecting to the remote machine over SSH.

								Note that the SSH key pair must @emph{not} be passphrase-protected, to

								allow non-interactive logins.


								@end table


								A number of optional fields may be specified:


								@table @code


								@item port

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


								@item private-key

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


								@item parallel-builds

								The number of builds that may run in parallel on the machine (1 by

								default.)


								@item speed

								A ``relative speed factor''.  The offload scheduler will tend to prefer

								machines with a higher speed factor.


								@item features

								A list of strings denoting specific features supported by the machine.

								An example is @code{"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.


								@end table

								@end deftp


								The @code{guix} command must be in the search path on the build

								machines, since offloading works by invoking the @code{guix archive} and

								@code{guix build} commands.


								There's one last thing to do once @file{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 need to generate a

								key pair to allow the daemon to export signed archives of files from the

								store (@pxref{Invoking guix archive}):


								@example

								# guix archive --generate-key

								@end example


								@noindent

								Thus, when receiving files, a machine's build daemon can make sure they

								are genuine, have not been tampered with, and that they are signed by an

								authorized key.


								@node Invoking guix-daemon

								@section Invoking @command{guix-daemon}


								The @command{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 @code{root} like this:


								@example

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

								@end example


								@noindent

								For details on how to set it up, @pxref{Setting Up the Daemon}.


								@cindex chroot

								@cindex container, build environment

								@cindex build environment

								@cindex reproducible builds

								By default, @command{guix-daemon} launches build processes under

								different UIDs, taken from the build group specified with

								@code{--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

								(@pxref{Programming Interface, derivation}), plus a set of specific

								system directories.  By default, the latter contains @file{/dev} and

								@file{/dev/pts}.  Furthermore, on GNU/Linux, the build environment is a

								@dfn{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 (@pxref{Features}).


								When the daemon performs a build on behalf of the user, it creates a

								build directory under @file{/tmp} or under the directory specified by

								its @code{TMPDIR} environment variable; this directory is shared with

								the container for the duration of the build.  Be aware that using a

								directory other than @file{/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 @code{sun_path}, which

								it would otherwise not hit.


								The build directory is automatically deleted upon completion, unless the

								build failed and the client specified @option{--keep-failed}

								(@pxref{Invoking guix build, @option{--keep-failed}}).


								The following command-line options are supported:


								@table @code

								@item --build-users-group=@var{group}

								Take users from @var{group} to run build processes (@pxref{Setting Up

								the Daemon, build users}).


								@item --no-substitutes

								@cindex substitutes

								Do not use substitutes for build products.  That is, always build things

								locally instead of allowing downloads of pre-built binaries

								(@pxref{Substitutes}).


								By default substitutes are used, unless the client---such as the

								@command{guix package} command---is explicitly invoked with

								@code{--no-substitutes}.


								When the daemon runs with @code{--no-substitutes}, clients can still

								explicitly enable substitution @i{via} the @code{set-build-options}

								remote procedure call (@pxref{The Store}).


								@item --substitute-urls=@var{urls}

								Consider @var{urls} the default whitespace-separated list of substitute

								source URLs.  When this option is omitted, @indicateurl{http://hydra.gnu.org}

								is used.


								This means that substitutes may be downloaded from @var{urls}, as long

								as they are signed by a trusted signature (@pxref{Substitutes}).


								@cindex build hook

								@item --no-build-hook

								Do not use the @dfn{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 (@pxref{Daemon Offload Setup}).


								@item --cache-failures

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


								@item --cores=@var{n}

								@itemx -c @var{n}

								Use @var{n} CPU cores to build each derivation; @code{0} means as many

								as available.


								The default value is @code{0}, but it may be overridden by clients, such

								as the @code{--cores} option of @command{guix build} (@pxref{Invoking

								guix build}).


								The effect is to define the @code{NIX_BUILD_CORES} environment variable

								in the build process, which can then use it to exploit internal

								parallelism---for instance, by running @code{make -j$NIX_BUILD_CORES}.


								@item --max-jobs=@var{n}

								@itemx -M @var{n}

								Allow at most @var{n} build jobs in parallel.  The default value is

								@code{1}.  Setting it to @code{0} means that no builds will be performed

								locally; instead, the daemon will offload builds (@pxref{Daemon Offload

								Setup}), or simply fail.


								@item --debug

								Produce debugging output.


								This is useful to debug daemon start-up issues, but then it may be

								overridden by clients, for example the @code{--verbosity} option of

								@command{guix build} (@pxref{Invoking guix build}).


								@item --chroot-directory=@var{dir}

								Add @var{dir} to the build chroot.


								Doing this may change the result of build processes---for instance if

								they use optional dependencies found in @var{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.


								@item --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 @command{guix-daemon} is running under an unprivileged user

								account.


								@item --disable-log-compression

								Disable compression of the build logs.


								Unless @code{--lose-logs} is used, all the build logs are kept in the

								@var{localstatedir}.  To save space, the daemon automatically compresses

								them with bzip2 by default.  This option disables that.


								@item --disable-deduplication

								@cindex 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.


								@item --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 @code{.drv} files.  The default is ``no'',

								meaning that derivation outputs are kept only if they are GC roots.


								@item --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., @code{.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 @code{--gc-keep-derivations} and

								@code{--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.


								@item --impersonate-linux-2.6

								On Linux-based systems, impersonate Linux 2.6.  This means that the

								kernel's @code{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.


								@item --lose-logs

								Do not keep build logs.  By default they are kept under

								@code{@var{localstatedir}/guix/log}.


								@item --system=@var{system}

								Assume @var{system} as the current system type.  By default it is the

								architecture/kernel pair found at configure time, such as

								@code{x86_64-linux}.


								@item --listen=@var{socket}

								Listen for connections on @var{socket}, the file name of a Unix-domain

								socket.  The default socket is

								@file{@var{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.

								@end table


								@c *********************************************************************

								@node Package Management

								@chapter 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

								(@pxref{Invoking guix package, @code{guix package}}), and a visual user

								interface in Emacs (@pxref{Emacs Interface}).


								@menu

								* Features::                    How Guix will make your life brighter.

								* Invoking guix package::       Package installation, removal, etc.

								* Emacs Interface::             Package management from Emacs.

								* Substitutes::                 Downloading pre-built binaries.

								* Packages with Multiple Outputs::  Single source package, multiple outputs.

								* Invoking guix gc::            Running the garbage collector.

								* Invoking guix pull::          Fetching the latest Guix and distribution.

								* Invoking guix archive::       Exporting and importing store files.

								@end menu


								@node Features

								@section Features


								When using Guix, each package ends up in the @dfn{package store}, in its

								own directory---something that resembles

								@file{/gnu/store/xxx-package-1.2}, where @code{xxx} is a base32 string

								(note that Guix comes with an Emacs extension to shorten those file

								names, @pxref{Emacs Prettify}.)


								Instead of referring to these directories, users have their own

								@dfn{profile}, which points to the packages that they actually want to

								use.  These profiles are stored within each user's home directory, at

								@code{$HOME/.guix-profile}.


								For example, @code{alice} installs GCC 4.7.2.  As a result,

								@file{/home/alice/.guix-profile/bin/gcc} points to

								@file{/gnu/store/@dots{}-gcc-4.7.2/bin/gcc}.  Now, on the same machine,

								@code{bob} had already installed GCC 4.8.0.  The profile of @code{bob}

								simply continues to point to

								@file{/gnu/store/@dots{}-gcc-4.8.0/bin/gcc}---i.e., both versions of GCC

								coexist on the same system without any interference.


								The @command{guix package} command is the central tool to manage

								packages (@pxref{Invoking guix package}).  It operates on those per-user

								profiles, and can be used @emph{with normal user privileges}.


								The command provides the obvious install, remove, and upgrade

								operations.  Each invocation is actually a @emph{transaction}: either

								the specified operation succeeds, or nothing happens.  Thus, if the

								@command{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 @emph{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

								(@pxref{Using the Configuration System}).


								All those packages in the package store may be @emph{garbage-collected}.

								Guix can determine which packages are still referenced by the user

								profiles, and remove those that are provably no longer referenced

								(@pxref{Invoking guix gc}).  Users may also explicitly remove old

								generations of their profile so that the packages they refer to can be

								collected.


								@cindex reproducibility

								@cindex reproducible builds

								Finally, Guix takes a @dfn{purely functional} approach to package

								management, as described in the introduction (@pxref{Introduction}).

								Each @file{/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 @dfn{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 (@pxref{Invoking guix-daemon, container}).


								@cindex substitutes

								This foundation allows Guix to support @dfn{transparent binary/source

								deployment}.  When a pre-built binary for a @file{/gnu/store} item is

								available from an external source---a @dfn{substitute}, Guix just

								downloads it and unpacks it;

								otherwise, it builds the package from source, locally

								(@pxref{Substitutes}).


								Control over the build environment is a feature that is also useful for

								developers.  The @command{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 (@pxref{Invoking guix environment}).


								@node Invoking guix package

								@section Invoking @command{guix package}


								The @command{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 (@pxref{Features}).  Its syntax

								is:


								@example

								guix package @var{options}

								@end example


								Primarily, @var{options} specifies the operations to be performed during

								the transaction.  Upon completion, a new profile is created, but

								previous @dfn{generations} of the profile remain available, should the user

								want to roll back.


								For example, to remove @code{lua} and install @code{guile} and

								@code{guile-cairo} in a single transaction:


								@example

								guix package -r lua -i guile guile-cairo

								@end example


								@command{guix package} also supports a @dfn{declarative approach}

								whereby the user specifies the exact set of packages to be available and

								passes it @i{via} the @option{--manifest} option

								(@pxref{profile-manifest, @option{--manifest}}).


								For each user, a symlink to the user's default profile is automatically

								created in @file{$HOME/.guix-profile}.  This symlink always points to the

								current generation of the user's default profile.  Thus, users can add

								@file{$HOME/.guix-profile/bin} to their @code{PATH} environment

								variable, and so on.

								@cindex search paths

								If you are not using the Guix System Distribution, consider adding the

								following lines to your @file{~/.bash_profile} (@pxref{Bash Startup

								Files,,, bash, The GNU Bash Reference Manual}) so that newly-spawned

								shells get all the right environment variable definitions:


								@example

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

								source "$HOME/.guix-profile/etc/profile"

								@end example


								In a multi-user setup, user profiles are stored in a place registered as

								a @dfn{garbage-collector root}, which @file{$HOME/.guix-profile} points

								to (@pxref{Invoking guix gc}).  That directory is normally

								@code{@var{localstatedir}/profiles/per-user/@var{user}}, where

								@var{localstatedir} is the value passed to @code{configure} as

								@code{--localstatedir}, and @var{user} is the user name.  The

								@file{per-user} directory is created when @command{guix-daemon} is

								started, and the @var{user} sub-directory is created by @command{guix

								package}.


								The @var{options} can be among the following:


								@table @code


								@item --install=@var{package} @dots{}

								@itemx -i @var{package} @dots{}

								Install the specified @var{package}s.


								Each @var{package} may specify either a simple package name, such as

								@code{guile}, or a package name followed by a hyphen and version number,

								such as @code{guile-1.8.8} or simply @code{guile-1.8} (in the latter

								case, the newest version prefixed by @code{1.8} is selected.)


								If no version number is specified, the

								newest available version will be selected.  In addition, @var{package}

								may contain a colon, followed by the name of one of the outputs of the

								package, as in @code{gcc:doc} or @code{binutils-2.22:lib}

								(@pxref{Packages with Multiple Outputs}).  Packages with a corresponding

								name (and optionally version) are searched for among the GNU

								distribution modules (@pxref{Package Modules}).


								@cindex propagated inputs

								Sometimes packages have @dfn{propagated inputs}: these are dependencies

								that automatically get installed along with the required package

								(@pxref{package-propagated-inputs, @code{propagated-inputs} in

								@code{package} objects}, for information about propagated inputs in

								package definitions).


								@anchor{package-cmd-propagated-inputs}

								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

								@code{--search-paths} below).  Any missing or possibly incorrect

								environment variable definitions are reported here.


								@c XXX: keep me up-to-date

								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.


								@item --install-from-expression=@var{exp}

								@itemx -e @var{exp}

								Install the package @var{exp} evaluates to.


								@var{exp} must be a Scheme expression that evaluates to a

								@code{<package>} object.  This option is notably useful to disambiguate

								between same-named variants of a package, with expressions such as

								@code{(@@ (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.


								@item --remove=@var{package} @dots{}

								@itemx -r @var{package} @dots{}

								Remove the specified @var{package}s.


								As for @code{--install}, each @var{package} may specify a version number

								and/or output name in addition to the package name.  For instance,

								@code{-r glibc:debug} would remove the @code{debug} output of

								@code{glibc}.


								@item --upgrade[=@var{regexp} @dots{}]

								@itemx -u [@var{regexp} @dots{}]

								Upgrade all the installed packages.  If one or more @var{regexp}s are

								specified, upgrade only installed packages whose name matches a

								@var{regexp}.  Also see the @code{--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 @command{guix pull} (@pxref{Invoking guix

								pull}).


								@item --do-not-upgrade[=@var{regexp} @dots{}]

								When used together with the @code{--upgrade} option, do @emph{not}

								upgrade any packages whose name matches a @var{regexp}.  For example, to

								upgrade all packages in the current profile except those containing the

								substring ``emacs'':


								@example

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

								@end example


								@item @anchor{profile-manifest}--manifest=@var{file}

								@itemx -m @var{file}

								@cindex profile declaration

								@cindex profile manifest

								Create a new generation of the profile from the manifest object

								returned by the Scheme code in @var{file}.


								This allows you to @emph{declare} the profile's contents rather than

								constructing it through a sequence of @code{--install} and similar

								commands.  The advantage is that @var{file} can be put under version

								control, copied to different machines to reproduce the same profile, and

								so on.


								@c FIXME: Add reference to (guix profile) documentation when available.

								@var{file} must return a @dfn{manifest} object, which is roughly a list

								of packages:


								@findex packages->manifest

								@example

								(use-package-modules guile emacs)


								(packages->manifest

								 (list emacs

								       guile-2.0

								       ;; Use a specific package output.

								       (list guile-2.0 "debug")))

								@end example


								@item --roll-back

								Roll back to the previous @dfn{generation} of the profile---i.e., undo

								the last transaction.


								When combined with options such as @code{--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 @dfn{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.


								@item --switch-generation=@var{pattern}

								@itemx -S @var{pattern}

								Switch to a particular generation defined by @var{pattern}.


								@var{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 @code{--roll-back}, use

								@code{--switch-generation=+1}.


								The difference between @code{--roll-back} and

								@code{--switch-generation=-1} is that @code{--switch-generation} will

								not make a zeroth generation, so if a specified generation does not

								exist, the current generation will not be changed.


								@item --search-paths[=@var{kind}]

								@cindex search paths

								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 @dfn{search paths} for files used by some

								of the installed packages.


								For example, GCC needs the @code{CPATH} and @code{LIBRARY_PATH}

								environment variables to be defined so it can look for headers and

								libraries in the user's profile (@pxref{Environment Variables,,, gcc,

								Using the GNU Compiler Collection (GCC)}).  If GCC and, say, the C

								library are installed in the profile, then @code{--search-paths} will

								suggest setting these variables to @code{@var{profile}/include} and

								@code{@var{profile}/lib}, respectively.


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

								shell:


								@example

								$ eval `guix package --search-paths`

								@end example


								@var{kind} may be one of @code{exact}, @code{prefix}, or @code{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, @var{kind} defaults to @code{exact}.


								@item --profile=@var{profile}

								@itemx -p @var{profile}

								Use @var{profile} instead of the user's default profile.


								@item --verbose

								Produce verbose output.  In particular, emit the environment's build log

								on the standard error port.


								@item --bootstrap

								Use the bootstrap Guile to build the profile.  This option is only

								useful to distribution developers.


								@end table


								In addition to these actions @command{guix package} supports the

								following options to query the current state of a profile, or the

								availability of packages:


								@table @option


								@item --search=@var{regexp}

								@itemx -s @var{regexp}

								List the available packages whose name, synopsis, or description matches

								@var{regexp}.  Print all the meta-data of matching packages in

								@code{recutils} format (@pxref{Top, GNU recutils databases,, recutils,

								GNU recutils manual}).


								This allows specific fields to be extracted using the @command{recsel}

								command, for instance:


								@example

								$ guix package -s malloc | recsel -p name,version

								name: glibc

								version: 2.17


								name: libgc

								version: 7.2alpha6

								@end example


								Similarly, to show the name of all the packages available under the

								terms of the GNU@tie{}LGPL version 3:


								@example

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

								name: elfutils


								name: gmp

								@dots{}

								@end example


								@item --show=@var{package}

								Show details about @var{package}, taken from the list of available packages, in

								@code{recutils} format (@pxref{Top, GNU recutils databases,, recutils, GNU

								recutils manual}).


								@example

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

								name: python

								version: 2.7.6


								name: python

								version: 3.3.5

								@end example


								You may also specify the full name of a package to only get details about a

								specific version of it:

								@example

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

								name: python

								version: 3.3.5

								@end example


								@item --list-installed[=@var{regexp}]

								@itemx -I [@var{regexp}]

								List the currently installed packages in the specified profile, with the

								most recently installed packages shown last.  When @var{regexp} is

								specified, list only installed packages whose name matches @var{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, @code{out} for the default output,

								@code{include} for its headers, etc.), and the path of this package in

								the store.


								@item --list-available[=@var{regexp}]

								@itemx -A [@var{regexp}]

								List packages currently available in the distribution for this system

								(@pxref{GNU Distribution}).  When @var{regexp} is specified, list only

								installed packages whose name matches @var{regexp}.


								For each package, print the following items separated by tabs: its name,

								its version string, the parts of the package (@pxref{Packages with

								Multiple Outputs}), and the source location of its definition.


								@item --list-generations[=@var{pattern}]

								@itemx -l [@var{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 (@pxref{Packages with Multiple Outputs}), and the

								location of this package in the store.


								When @var{pattern} is used, the command returns only matching

								generations.  Valid patterns include:


								@itemize

								@item @emph{Integers and comma-separated integers}.  Both patterns denote

								generation numbers.  For instance, @code{--list-generations=1} returns

								the first one.


								And @code{--list-generations=1,8,2} outputs three generations in the

								specified order.  Neither spaces nor trailing commas are allowed.


								@item @emph{Ranges}.  @code{--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,

								@code{--list-generations=2..}, returns all generations starting from the

								second one.


								@item @emph{Durations}.  You can also get the last @emph{N}@tie{}days, weeks,

								or months by passing an integer along with the first letter of the

								duration.  For example, @code{--list-generations=20d} lists generations

								that are up to 20 days old.

								@end itemize


								@item --delete-generations[=@var{pattern}]

								@itemx -d [@var{pattern}]

								When @var{pattern} is omitted, delete all generations except the current

								one.


								This command accepts the same patterns as @option{--list-generations}.

								When @var{pattern} is specified, delete the matching generations.  When

								@var{pattern} specifies a duration, generations @emph{older} than the

								specified duration match.  For instance, @code{--delete-generations=1m}

								deletes generations that are more than one month old.


								If the current generation matches, it is @emph{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.


								@end table


								Finally, since @command{guix package} may actually start build

								processes, it supports all the common build options that @command{guix

								build} supports (@pxref{Invoking guix build, common build options}).


								@include emacs.texi


								@node Substitutes

								@section Substitutes


								@cindex substitutes

								@cindex pre-built binaries

								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 @dfn{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

								(@pxref{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 @code{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

								@command{guix-daemon} the @code{--substitute-urls} option

								(@pxref{Invoking guix-daemon}).


								@cindex security

								@cindex digital signatures

								To allow Guix to download substitutes from @code{hydra.gnu.org}, you

								must add its public key to the access control list (ACL) of archive

								imports, using the @command{guix archive} command (@pxref{Invoking guix

								archive}).  Doing so implies that you trust @code{hydra.gnu.org} to not

								be compromised and to serve genuine substitutes.


								This public key is installed along with Guix, in

								@code{@var{prefix}/share/guix/hydra.gnu.org.pub}, where @var{prefix} is

								the installation prefix of Guix.  If you installed Guix from source,

								make sure you checked the GPG signature of

								@file{guix-@value{VERSION}.tar.gz}, which contains this public key file.

								Then, you can run something like this:


								@example

								# guix archive --authorize < hydra.gnu.org.pub

								@end example


								Once this is in place, the output of a command like @code{guix build}

								should change from something like:


								@example

								$ 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

								@dots{}

								@end example


								@noindent

								to something like:


								@example

								$ 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

								@dots{}

								@end example


								@noindent

								This indicates that substitutes from @code{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

								@code{guix-daemon} with @code{--no-substitutes} (@pxref{Invoking

								guix-daemon}).  It can also be disabled temporarily by passing the

								@code{--no-substitutes} option to @command{guix package}, @command{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 @code{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 @code{hydra.gnu.org} is less of an

								interesting target.  One way to help is by publishing the software you

								build using @command{guix publish} so that others have one more choice

								of server to download substitutes from (@pxref{Invoking guix publish}).


								Guix has the foundations to maximize build reproducibility

								(@pxref{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 @email{guix-devel@@gnu.org}.


								@node Packages with Multiple Outputs

								@section Packages with Multiple Outputs


								@cindex multiple-output packages

								@cindex package outputs


								Often, packages defined in Guix have a single @dfn{output}---i.e., the

								source package leads exactly one directory in the store.  When running

								@command{guix package -i glibc}, one installs the default output of the

								GNU libc package; the default output is called @code{out}, but its name

								can be omitted as shown in this command.  In this particular case, the

								default output of @code{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 @code{doc}.  To install the main GLib output,

								which contains everything but the documentation, one would run:


								@example

								guix package -i glib

								@end example


								The command to install its documentation is:


								@example

								guix package -i glib:doc

								@end example


								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.


								There are several such multiple-output packages in the GNU distribution.

								Other conventional output names include @code{lib} for libraries and

								possibly header files, @code{bin} for stand-alone programs, and

								@code{debug} for debugging information (@pxref{Installing Debugging

								Files}).  The outputs of a packages are listed in the third column of

								the output of @command{guix package --list-available} (@pxref{Invoking

								guix package}).


								@node Invoking guix gc

								@section Invoking @command{guix gc}


								@cindex garbage collector

								Packages that are installed but not used may be @dfn{garbage-collected}.

								The @command{guix gc} command allows users to explicitly run the garbage

								collector to reclaim space from the @file{/gnu/store} directory.  It is

								the @emph{only} way to remove files from @file{/gnu/store}---removing

								files or directories manually may break it beyond repair!


								The garbage collector has a set of known @dfn{roots}: any file under

								@file{/gnu/store} reachable from a root is considered @dfn{live} and

								cannot be deleted; any other file is considered @dfn{dead} and may be

								deleted.  The set of garbage collector roots includes default user

								profiles, and may be augmented with @command{guix build --root}, for

								example (@pxref{Invoking guix build}).


								Prior to running @code{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 @code{guix package --delete-generations}

								(@pxref{Invoking guix package}).


								The @command{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 @code{--delete} option), to print garbage-collector

								information, or for more advanced queries.  The garbage collection

								options are as follows:


								@table @code

								@item --collect-garbage[=@var{min}]

								@itemx -C [@var{min}]

								Collect garbage---i.e., unreachable @file{/gnu/store} files and

								sub-directories.  This is the default operation when no option is

								specified.


								When @var{min} is given, stop once @var{min} bytes have been collected.

								@var{min} may be a number of bytes, or it may include a unit as a

								suffix, such as @code{MiB} for mebibytes and @code{GB} for gigabytes

								(@pxref{Block size, size specifications,, coreutils, GNU Coreutils}).


								When @var{min} is omitted, collect all the garbage.


								@item --delete

								@itemx -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.


								@item --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.


								@item --list-live

								Show the list of live store files and directories.


								@end table


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


								@table @code


								@item --references

								@itemx --referrers

								List the references (respectively, the referrers) of store files given

								as arguments.


								@item --requisites

								@itemx -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

								@dfn{transitive closure} of the store files.


								@end table


								Lastly, the following options allow you to check the integrity of the

								store and to control disk usage.


								@table @option


								@item --verify[=@var{options}]

								@cindex integrity, of the store

								@cindex integrity checking

								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 @file{/gnu/store}.


								When provided, @var{options} must a comma-separated list containing one

								or more of @code{contents} and @code{repair}.


								When passing @option{--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 @emph{all the files in the store}, this command can take a

								long time, especially on systems with a slow disk drive.


								@cindex repairing the store

								Using @option{--verify=repair} or @option{--verify=contents,repair}

								causes the daemon to try to repair corrupt store items by fetching

								substitutes for them (@pxref{Substitutes}).  Because repairing is not

								atomic, and thus potentially dangerous, it is available only to the

								system administrator.


								@item --optimize

								@cindex deduplication

								Optimize the store by hard-linking identical files---this is

								@dfn{deduplication}.


								The daemon performs deduplication after each successful build or archive

								import, unless it was started with @code{--disable-deduplication}

								(@pxref{Invoking guix-daemon, @code{--disable-deduplication}}).  Thus,

								this option is primarily useful when the daemon was running with

								@code{--disable-deduplication}.


								@end table


								@node Invoking guix pull

								@section Invoking @command{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 @command{guix

								pull}: the command downloads the latest Guix source code and package

								descriptions, and deploys it.


								On completion, @command{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 @command{guix} sub-commands added by the update also

								become available.


								The @command{guix pull} command is usually invoked with no arguments,

								but it supports the following options:


								@table @code

								@item --verbose

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


								@item --url=@var{url}

								Download the source tarball of Guix from @var{url}.


								By default, the tarball is taken from its canonical address at

								@code{gnu.org}, for the stable branch of Guix.


								@item --bootstrap

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

								useful to Guix developers.

								@end table


								@node Invoking guix archive

								@section Invoking @command{guix archive}


								The @command{guix archive} command allows users to @dfn{export} files

								from the store into a single archive, and to later @dfn{import} them.

								In particular, it allows store files to be transferred from one machine

								to another machine's store.  For example, to transfer the @code{emacs}

								package to a machine connected over SSH, one would run:


								@example

								guix archive --export -r emacs | ssh the-machine guix archive --import

								@end example


								@noindent

								Similarly, a complete user profile may be transferred from one machine

								to another like this:


								@example

								guix archive --export -r $(readlink -f ~/.guix-profile) | \

								  ssh the-machine guix-archive --import

								@end example


								@noindent

								However, note that, in both examples, all of @code{emacs} and the

								profile as well as all of their dependencies are transferred (due to

								@code{-r}), regardless of what is already available in the target

								machine's store.  The @code{--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.

								@c FIXME: Add xref to daemon doc about signatures.


								The main options are:


								@table @code

								@item --export

								Export the specified store files or packages (see below.)  Write the

								resulting archive to the standard output.


								Dependencies are @emph{not} included in the output, unless

								@code{--recursive} is passed.


								@item -r

								@itemx --recursive

								When combined with @code{--export}, this instructs @command{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.


								@item --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 @code{--authorize} below.)


								@item --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.


								@item --generate-key[=@var{parameters}]

								@cindex signing, archives

								Generate a new key pair for the daemons.  This is a prerequisite before

								archives can be exported with @code{--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 @file{/etc/guix}, in

								@file{signing-key.pub} (public key) and @file{signing-key.sec} (private

								key, which must be kept secret.)  When @var{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, @var{parameters} can specify

								@code{genkey} parameters suitable for Libgcrypt (@pxref{General

								public-key related Functions, @code{gcry_pk_genkey},, gcrypt, The

								Libgcrypt Reference Manual}).


								@item --authorize

								@cindex authorizing, archives

								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 @file{signing-key.pub} file.


								The list of authorized keys is kept in the human-editable file

								@file{/etc/guix/acl}.  The file contains

								@url{http://people.csail.mit.edu/rivest/Sexp.txt, ``advanced-format

								s-expressions''} and is structured as an access-control list in the

								@url{http://theworld.com/~cme/spki.txt, Simple Public-Key Infrastructure

								(SPKI)}.

								@end table


								To export store files as an archive to the standard output, run:


								@example

								guix archive --export @var{options} @var{specifications}...

								@end example


								@var{specifications} may be either store file names or package

								specifications, as for @command{guix package} (@pxref{Invoking guix

								package}).  For instance, the following command creates an archive

								containing the @code{gui} output of the @code{git} package and the main

								output of @code{emacs}:


								@example

								guix archive --export git:gui /gnu/store/...-emacs-24.3 > great.nar

								@end example


								If the specified packages are not built yet, @command{guix archive}

								automatically builds them.  The build process may be controlled with the

								same options that can be passed to the @command{guix build} command

								(@pxref{Invoking guix build, common build options}).


								@c *********************************************************************

								@node Programming Interface

								@chapter 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

								@file{/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.


								@cindex derivation

								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 @dfn{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 @emph{derive} from them.


								This chapter describes all these APIs in turn, starting from high-level

								package definitions.


								@menu

								* Defining Packages::           Defining new packages.

								* Build Systems::               Specifying how packages are built.

								* The Store::                   Manipulating the package store.

								* Derivations::                 Low-level interface to package derivations.

								* The Store Monad::             Purely functional interface to the store.

								* G-Expressions::               Manipulating build expressions.

								@end menu


								@node Defining Packages

								@section Defining Packages


								The high-level interface to package definitions is implemented in the

								@code{(guix packages)} and @code{(guix build-system)} modules.  As an

								example, the package definition, or @dfn{recipe}, for the GNU Hello

								package looks like this:


								@example

								(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+)))

								@end example


								@noindent

								Without being a Scheme expert, the reader may have guessed the meaning

								of the various fields here.  This expression binds variable @code{hello}

								to a @code{<package>} object, which is essentially a record

								(@pxref{SRFI-9, Scheme records,, guile, GNU Guile Reference Manual}).

								This package object can be inspected using procedures found in the

								@code{(guix packages)} module; for instance, @code{(package-name hello)}

								returns---surprise!---@code{"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

								@code{guix import} command (@pxref{Invoking guix import}).


								In the example above, @var{hello} is defined into a module of its own,

								@code{(gnu packages hello)}.  Technically, this is not strictly

								necessary, but it is convenient to do so: all the packages defined in

								modules under @code{(gnu packages @dots{})} are automatically known to

								the command-line tools (@pxref{Package Modules}).


								There are a few points worth noting in the above package definition:


								@itemize

								@item

								The @code{source} field of the package is an @code{<origin>} object

								(@pxref{origin Reference}, for the complete reference).

								Here, the @code{url-fetch} method from @code{(guix download)} is used,

								meaning that the source is a file to be downloaded over FTP or HTTP.


								The @code{mirror://gnu} prefix instructs @code{url-fetch} to use one of

								the GNU mirrors defined in @code{(guix download)}.


								The @code{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 @code{(base32 @dots{})} form introduces the

								base32 representation of the hash.  You can obtain this information with

								@code{guix download} (@pxref{Invoking guix download}) and @code{guix

								hash} (@pxref{Invoking guix hash}).


								@cindex patches

								When needed, the @code{origin} form can also have a @code{patches} field

								listing patches to be applied, and a @code{snippet} field giving a

								Scheme expression to modify the source code.


								@item

								@cindex GNU Build System

								The @code{build-system} field specifies the procedure to build the

								package (@pxref{Build Systems}).  Here, @var{gnu-build-system}

								represents the familiar GNU Build System, where packages may be

								configured, built, and installed with the usual @code{./configure &&

								make && make check && make install} command sequence.


								@item

								The @code{arguments} field specifies options for the build system

								(@pxref{Build Systems}).  Here it is interpreted by

								@var{gnu-build-system} as a request run @file{configure} with the

								@code{--enable-silent-rules} flag.


								@item

								The @code{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 @code{"gawk"} whose value is that of the @var{gawk}

								variable; @var{gawk} is itself bound to a @code{<package>} object.


								Note that GCC, Coreutils, Bash, and other essential tools do not need to

								be specified as inputs here.  Instead, @var{gnu-build-system} takes care

								of ensuring that they are present (@pxref{Build Systems}).


								However, any other dependencies need to be specified in the

								@code{inputs} field.  Any dependency not specified here will simply be

								unavailable to the build process, possibly leading to a build failure.

								@end itemize


								@xref{package Reference}, for a full description of possible fields.


								Once a package definition is in place, the

								package may actually be built using the @code{guix build} command-line

								tool (@pxref{Invoking guix build}).  @xref{Packaging Guidelines}, for

								more information on how to test package definitions, and

								@ref{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 @command{guix refresh} command

								(@pxref{Invoking guix refresh}).


								Behind the scenes, a derivation corresponding to the @code{<package>}

								object is first computed by the @code{package-derivation} procedure.

								That derivation is stored in a @code{.drv} file under @file{/gnu/store}.

								The build actions it prescribes may then be realized by using the

								@code{build-derivations} procedure (@pxref{The Store}).


								@deffn {Scheme Procedure} package-derivation @var{store} @var{package} [@var{system}]

								Return the @code{<derivation>} object of @var{package} for @var{system}

								(@pxref{Derivations}).


								@var{package} must be a valid @code{<package>} object, and @var{system}

								must be a string denoting the target system type---e.g.,

								@code{"x86_64-linux"} for an x86_64 Linux-based GNU system.  @var{store}

								must be a connection to the daemon, which operates on the store

								(@pxref{The Store}).

								@end deffn


								@noindent

								@cindex cross-compilation

								Similarly, it is possible to compute a derivation that cross-builds a

								package for some other system:


								@deffn {Scheme Procedure} package-cross-derivation @var{store} @

								            @var{package} @var{target} [@var{system}]

								Return the @code{<derivation>} object of @var{package} cross-built from

								@var{system} to @var{target}.


								@var{target} must be a valid GNU triplet denoting the target hardware

								and operating system, such as @code{"mips64el-linux-gnu"}

								(@pxref{Configuration Names, GNU configuration triplets,, configure, GNU

								Configure and Build System}).

								@end deffn


								@menu

								* package Reference ::          The package data type.

								* origin Reference::            The origin data type.

								@end menu


								@node package Reference

								@subsection @code{package} Reference


								This section summarizes all the options available in @code{package}

								declarations (@pxref{Defining Packages}).


								@deftp {Data Type} package

								This is the data type representing a package recipe.


								@table @asis

								@item @code{name}

								The name of the package, as a string.


								@item @code{version}

								The version of the package, as a string.


								@item @code{source}

								An origin object telling how the source code for the package should be

								acquired (@pxref{origin Reference}).


								@item @code{build-system}

								The build system that should be used to build the package (@pxref{Build

								Systems}).


								@item @code{arguments} (default: @code{'()})

								The arguments that should be passed to the build system.  This is a

								list, typically containing sequential keyword-value pairs.


								@item @code{inputs} (default: @code{'()})

								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 @code{"out"}.


								@item @anchor{package-propagated-inputs}@code{propagated-inputs} (default: @code{'()})

								@cindex propagated inputs

								This field is like @code{inputs}, but the specified packages will be

								force-installed alongside the package they belong to

								(@pxref{package-cmd-propagated-inputs, @command{guix package}}, for

								information on how @command{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.


								@item @code{native-inputs} (default: @code{'()})

								This field is like @code{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.  @command{guix lint} can report likely mistakes in this area

								(@pxref{Invoking guix lint}).


								@item @code{self-native-input?} (default: @code{#f})

								This is a Boolean field telling whether the package should use itself as

								a native input when cross-compiling.


								@item @code{outputs} (default: @code{'("out")})

								The list of output names of the package.  @xref{Packages with Multiple

								Outputs}, for typical uses of additional outputs.


								@item @code{native-search-paths} (default: @code{'()})

								@itemx @code{search-paths} (default: @code{'()})

								A list of @code{search-path-specification} objects describing

								search-path environment variables honored by the package.


								@item @code{replacement} (default: @code{#f})

								This must either @code{#f} or a package object that will be used as a

								@dfn{replacement} for this package.  @xref{Security Updates, grafts},

								for details.


								@item @code{synopsis}

								A one-line description of the package.


								@item @code{description}

								A more elaborate description of the package.


								@item @code{license}

								The license of the package; a value from @code{(guix licenses)}.


								@item @code{home-page}

								The URL to the home-page of the package, as a string.


								@item @code{supported-systems} (default: @var{%supported-systems})

								The list of systems supported by the package, as strings of the form

								@code{architecture-kernel}, for example @code{"x86_64-linux"}.


								@item @code{maintainers} (default: @code{'()})

								The list of maintainers of the package, as @code{maintainer} objects.


								@item @code{location} (default: source location of the @code{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.

								@end table

								@end deftp


								@node origin Reference

								@subsection @code{origin} Reference


								This section summarizes all the options available in @code{origin}

								declarations (@pxref{Defining Packages}).


								@deftp {Data Type} origin

								This is the data type representing a source code origin.


								@table @asis

								@item @code{uri}

								An object containing the URI of the source.  The object type depends on

								the @code{method} (see below).  For example, when using the

								@var{url-fetch} method of @code{(guix download)}, the valid @code{uri}

								values are: a URL represented as a string, or a list thereof.


								@item @code{method}

								A procedure that will handle the URI.


								Examples include:


								@table @asis

								@item @var{url-fetch} from @code{(guix download)}

								download a file the HTTP, HTTPS, or FTP URL specified in the

								@code{uri} field;


								@item @var{git-fetch} from @code{(guix git-download)}

								clone the Git version control repository, and check out the revision

								specified in the @code{uri} field as a @code{git-reference} object; a

								@code{git-reference} looks like this:


								@example

								(git-reference

								  (url "git://git.debian.org/git/pkg-shadow/shadow")

								  (commit "v4.1.5.1"))

								@end example

								@end table


								@item @code{sha256}

								A bytevector containing the SHA-256 hash of the source.  Typically the

								@code{base32} form is used here to generate the bytevector from a

								base-32 string.


								@item @code{file-name} (default: @code{#f})

								The file name under which the source code should be saved.  When this is

								@code{#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.


								@item @code{patches} (default: @code{'()})

								A list of file names containing patches to be applied to the source.


								@item @code{snippet} (default: @code{#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.


								@item @code{patch-flags} (default: @code{'("-p1")})

								A list of command-line flags that should be passed to the @code{patch}

								command.


								@item @code{patch-inputs} (default: @code{#f})

								Input packages or derivations to the patching process.  When this is

								@code{#f}, the usual set of inputs necessary for patching are provided,

								such as GNU@tie{}Patch.


								@item @code{modules} (default: @code{'()})

								A list of Guile modules that should be loaded during the patching

								process and while running the code in the @code{snippet} field.


								@item @code{imported-modules} (default: @code{'()})

								The list of Guile modules to import in the patch derivation, for use by

								the @code{snippet}.


								@item @code{patch-guile} (default: @code{#f})

								The Guile package that should be used in the patching process.  When

								this is @code{#f}, a sensible default is used.

								@end table

								@end deftp


								@node Build Systems

								@section Build Systems


								@cindex build system

								Each package definition specifies a @dfn{build system} and arguments for

								that build system (@pxref{Defining Packages}).  This @code{build-system}

								field represents the build procedure of the package, as well implicit

								dependencies of that build procedure.


								Build systems are @code{<build-system>} objects.  The interface to

								create and manipulate them is provided by the @code{(guix build-system)}

								module, and actual build systems are exported by specific modules.


								@cindex bag (low-level package representation)

								Under the hood, build systems first compile package objects to

								@dfn{bags}.  A @dfn{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 (@pxref{Derivations}).


								Build systems accept an optional list of @dfn{arguments}.  In package

								definitions, these are passed @i{via} the @code{arguments} field

								(@pxref{Defining Packages}).  They are typically keyword arguments

								(@pxref{Optional Arguments, keyword arguments in Guile,, guile, GNU

								Guile Reference Manual}).  The value of these arguments is usually

								evaluated in the @dfn{build stratum}---i.e., by a Guile process launched

								by the daemon (@pxref{Derivations}).


								The main build system is @var{gnu-build-system}, which implements the

								standard build procedure for GNU packages and many other packages.  It

								is provided by the @code{(guix build-system gnu)} module.


								@defvr {Scheme Variable} gnu-build-system

								@var{gnu-build-system} represents the GNU Build System, and variants

								thereof (@pxref{Configuration, configuration and makefile conventions,,

								standards, GNU Coding Standards}).


								@cindex build phases

								In a nutshell, packages using it configured, built, and installed with

								the usual @code{./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 @dfn{phases},

								notably@footnote{Please see the @code{(guix build gnu-build-system)}

								modules for more details about the build phases.}:


								@table @code

								@item 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.


								@item patch-source-shebangs

								Patch shebangs encountered in source files so they refer to the right

								store file names.  For instance, this changes @code{#!/bin/sh} to

								@code{#!/gnu/store/@dots{}-bash-4.3/bin/sh}.


								@item configure

								Run the @file{configure} script with a number of default options, such

								as @code{--prefix=/gnu/store/@dots{}}, as well as the options specified

								by the @code{#:configure-flags} argument.


								@item build

								Run @code{make} with the list of flags specified with

								@code{#:make-flags}.  If the @code{#:parallel-builds?} argument is true

								(the default), build with @code{make -j}.


								@item check

								Run @code{make check}, or some other target specified with

								@code{#:test-target}, unless @code{#:tests? #f} is passed.  If the

								@code{#:parallel-tests?} argument is true (the default), run @code{make

								check -j}.


								@item install

								Run @code{make install} with the flags listed in @code{#:make-flags}.


								@item patch-shebangs

								Patch shebangs on the installed executable files.


								@item strip

								Strip debugging symbols from ELF files (unless @code{#:strip-binaries?}

								is false), copying them to the @code{debug} output when available

								(@pxref{Installing Debugging Files}).

								@end table


								@vindex %standard-phases

								The build-side module @code{(guix build gnu-build-system)} defines

								@var{%standard-phases} as the default list of build phases.

								@var{%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

								@code{#:phases} parameter.  For instance, passing:


								@example

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

								@end example


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

								@code{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 @code{(guix

								build-system gnu)} module for a complete list.)  We call these the

								@dfn{implicit inputs} of a package, because package definitions don't

								have to mention them.

								@end defvr


								Other @code{<build-system>} objects are defined to support other

								conventions and tools used by free software packages.  They inherit most

								of @var{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.


								@defvr {Scheme Variable} cmake-build-system

								This variable is exported by @code{(guix build-system cmake)}.  It

								implements the build procedure for packages using the

								@url{http://www.cmake.org, CMake build tool}.


								It automatically adds the @code{cmake} package to the set of inputs.

								Which package is used can be specified with the @code{#:cmake}

								parameter.


								The @code{#:configure-flags} parameter is taken as a list of flags

								passed to the @command{cmake} command.  The @code{#:build-type}

								parameter specifies in abstract terms the flags passed to the compiler;

								it defaults to @code{"RelWithDebInfo"} (short for ``release mode with

								debugging information''), which roughly means that code is compiled with

								@code{-O2 -g}, as is the case for Autoconf-based packages by default.

								@end defvr


								@defvr {Scheme Variable} glib-or-gtk-build-system

								This variable is exported by @code{(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

								@var{gnu-build-system}:


								@table @code

								@item glib-or-gtk-wrap

								The phase @code{glib-or-gtk-wrap} ensures that programs found under

								@file{bin/} are able to find GLib's ``schemas'' and

								@uref{https://developer.gnome.org/gtk3/stable/gtk-running.html, GTK+

								modules}.  This is achieved by wrapping the programs in launch scripts

								that appropriately set the @code{XDG_DATA_DIRS} and @code{GTK_PATH}

								environment variables.


								It is possible to exclude specific package outputs from that wrapping

								process by listing their names in the

								@code{#: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+.


								@item glib-or-gtk-compile-schemas

								The phase @code{glib-or-gtk-compile-schemas} makes sure that all GLib's

								@uref{https://developer.gnome.org/gio/stable/glib-compile-schemas.html,

								GSettings schemas} are compiled.  Compilation is performed by the

								@command{glib-compile-schemas} program.  It is provided by the package

								@code{glib:bin} which is automatically imported by the build system.

								The @code{glib} package providing @command{glib-compile-schemas} can be

								specified with the @code{#:glib} parameter.

								@end table


								Both phases are executed after the @code{install} phase.

								@end defvr


								@defvr {Scheme Variable} python-build-system

								This variable is exported by @code{(guix build-system python)}.  It

								implements the more or less standard build procedure used by Python

								packages, which consists in running @code{python setup.py build} and

								then @code{python setup.py install --prefix=/gnu/store/@dots{}}.


								For packages that install stand-alone Python programs under @code{bin/},

								it takes care of wrapping these programs so their @code{PYTHONPATH}

								environment variable points to all the Python libraries they depend on.


								Which Python package is used can be specified with the @code{#:python}

								parameter.

								@end defvr


								@defvr {Scheme Variable} perl-build-system

								This variable is exported by @code{(guix build-system perl)}.  It

								implements the standard build procedure for Perl packages, which either

								consists in running @code{perl Build.PL --prefix=/gnu/store/@dots{}},

								followed by @code{Build} and @code{Build install}; or in running

								@code{perl Makefile.PL PREFIX=/gnu/store/@dots{}}, followed by

								@code{make} and @code{make install}; depending on which of

								@code{Build.PL} or @code{Makefile.PL} is present in the package

								distribution.  Preference is given to the former if both @code{Build.PL}

								and @code{Makefile.PL} exist in the package distribution.  This

								preference can be reversed by specifying @code{#t} for the

								@code{#:make-maker?} parameter.


								The initial @code{perl Makefile.PL} or @code{perl Build.PL} invocation

								passes flags specified by the @code{#:make-maker-flags} or

								@code{#:module-build-flags} parameter, respectively.


								Which Perl package is used can be specified with @code{#:perl}.

								@end defvr


								@defvr {Scheme Variable} ruby-build-system

								This variable is exported by @code{(guix build-system ruby)}.  It

								implements the RubyGems build procedure used by Ruby packages, which

								involves running @code{gem build} followed by @code{gem install}.


								Which Ruby package is used can be specified with the @code{#:ruby}

								parameter.

								@end defvr


								@defvr {Scheme Variable} waf-build-system

								This variable is exported by @code{(guix build-system waf)}.  It

								implements a build procedure around the @code{waf} script.  The common

								phases---@code{configure}, @code{build}, and @code{install}---are

								implemented by passing their names as arguments to the @code{waf}

								script.


								The @code{waf} script is executed by the Python interpreter.  Which

								Python package is used to run the script can be specified with the

								@code{#:python} parameter.

								@end defvr


								@defvr {Scheme Variable} haskell-build-system

								This variable is exported by @code{(guix build-system haskell)}.  It

								implements the Cabal build procedure used by Haskell packages, which

								involves running @code{runhaskell Setup.hs configure

								--prefix=/gnu/store/@dots{}} and @code{runhaskell Setup.hs build}.

								Instead of installing the package by running @code{runhaskell Setup.hs

								install}, to avoid trying to register libraries in the read-only

								compiler store directory, the build system uses @code{runhaskell

								Setup.hs copy}, followed by @code{runhaskell Setup.hs register}.  In

								addition, the build system generates the package documentation by

								running @code{runhaskell Setup.hs haddock}, unless @code{#:haddock? #f}

								is passed.  Optional Haddock parameters can be passed with the help of

								the @code{#:haddock-flags} parameter.  If the file @code{Setup.hs} is

								not found, the build system looks for @code{Setup.lhs} instead.


								Which Haskell compiler is used can be specified with the @code{#:haskell}

								parameter which defaults to @code{ghc}.

								@end defvr


								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.


								@defvr {Scheme Variable} trivial-build-system

								This variable is exported by @code{(guix build-system trivial)}.


								This build system requires a @code{#:builder} argument.  This argument

								must be a Scheme expression that builds the package's output(s)---as

								with @code{build-expression->derivation} (@pxref{Derivations,

								@code{build-expression->derivation}}).

								@end defvr


								@node The Store

								@section The Store


								@cindex store

								@cindex store paths


								Conceptually, the @dfn{store} is where derivations that have been

								successfully built are stored---by default, under @file{/gnu/store}.

								Sub-directories in the store are referred to as @dfn{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 @emph{valid}

								store paths---paths that result from a successful build.


								The store is always accessed by the daemon on behalf of its clients

								(@pxref{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 @code{(guix store)} module provides procedures to connect to the

								daemon, and to perform RPCs.  These are described below.


								@deffn {Scheme Procedure} open-connection [@var{file}] [#:reserve-space? #t]

								Connect to the daemon over the Unix-domain socket at @var{file}.  When

								@var{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.


								@var{file} defaults to @var{%default-socket-path}, which is the normal

								location given the options that were passed to @command{configure}.

								@end deffn


								@deffn {Scheme Procedure} close-connection @var{server}

								Close the connection to @var{server}.

								@end deffn


								@defvr {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.

								@end defvr


								Procedures that make RPCs all take a server object as their first

								argument.


								@deffn {Scheme Procedure} valid-path? @var{server} @var{path}

								Return @code{#t} when @var{path} is a valid store path.

								@end deffn


								@deffn {Scheme Procedure} add-text-to-store @var{server} @var{name} @var{text} [@var{references}]

								Add @var{text} under file @var{name} in the store, and return its store

								path.  @var{references} is the list of store paths referred to by the

								resulting store path.

								@end deffn


								@deffn {Scheme Procedure} build-derivations @var{server} @var{derivations}

								Build @var{derivations} (a list of @code{<derivation>} objects or

								derivation paths), and return when the worker is done building them.

								Return @code{#t} on success.

								@end deffn


								Note that the @code{(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 (@pxref{The

								Store Monad}).


								@c FIXME

								@i{This section is currently incomplete.}


								@node Derivations

								@section Derivations


								@cindex derivations

								Low-level build actions and the environment in which they are performed

								are represented by @dfn{derivations}.  A derivation contain the

								following pieces of information:


								@itemize

								@item

								The outputs of the derivation---derivations produce at least one file or

								directory in the store, but may produce more.


								@item

								The inputs of the derivations, which may be other derivations or plain

								files in the store (patches, build scripts, etc.)


								@item

								The system type targeted by the derivation---e.g., @code{x86_64-linux}.


								@item

								The file name of a build script in the store, along with the arguments

								to be passed.


								@item

								A list of environment variables to be defined.


								@end itemize


								@cindex derivation path

								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 @code{.drv}---these files are referred to as @dfn{derivation

								paths}.  Derivations paths can be passed to the @code{build-derivations}

								procedure to perform the build actions they prescribe (@pxref{The

								Store}).


								The @code{(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 @code{derivation} procedure:


								@deffn {Scheme Procedure} derivation @var{store} @var{name} @var{builder} @

								  @var{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]

								Build a derivation with the given arguments, and return the resulting

								@code{<derivation>} object.


								When @var{hash} and @var{hash-algo} are given, a

								@dfn{fixed-output derivation} is created---i.e., one whose result is

								known in advance, such as a file download.  If, in addition,

								@var{recursive?} is true, then that fixed output may be an executable

								file or a directory and @var{hash} must be the hash of an archive

								containing this output.


								When @var{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 @var{allowed-references} is true, it must be a list of store items

								or outputs that the derivation's output may refer to.


								When @var{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 @var{hash} is true.  The main

								use is to allow variables such as @code{http_proxy} to be passed to

								derivations that download files.


								When @var{local-build?} is true, declare that the derivation is not a

								good candidate for offloading and should rather be built locally

								(@pxref{Daemon Offload Setup}).  This is the case for small derivations

								where the costs of data transfers would outweigh the benefits.

								@end deffn


								@noindent

								Here's an example with a shell script as its builder, assuming

								@var{store} is an open connection to the daemon, and @var{bash} points

								to a Bash executable in the store:


								@lisp

								(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"))))

								@result{} #<derivation /gnu/store/@dots{}-foo.drv => /gnu/store/@dots{}-foo>

								@end lisp


								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 @code{gexp->derivation}.  For more

								information, @pxref{G-Expressions}.


								Once upon a time, @code{gexp->derivation} did not exist and constructing

								derivations with build code written in Scheme was achieved with

								@code{build-expression->derivation}, documented below.  This procedure

								is now deprecated in favor of the much nicer @code{gexp->derivation}.


								@deffn {Scheme Procedure} build-expression->derivation @var{store} @

								       @var{name} @var{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] [#:guile-for-build #f]

								Return a derivation that executes Scheme expression @var{exp} as a

								builder for derivation @var{name}.  @var{inputs} must be a list of

								@code{(name drv-path sub-drv)} tuples; when @var{sub-drv} is omitted,

								@code{"out"} is assumed.  @var{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

								@var{exp}---e.g., @code{((guix build utils) (guix build

								gnu-build-system))}.


								@var{exp} is evaluated in an environment where @code{%outputs} is bound

								to a list of output/path pairs, and where @code{%build-inputs} is bound

								to a list of string/output-path pairs made from @var{inputs}.

								Optionally, @var{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 @var{exp} to @code{exit}; thus, when

								@var{exp} returns @code{#f}, the build is considered to have failed.


								@var{exp} is built using @var{guile-for-build} (a derivation).  When

								@var{guile-for-build} is omitted or is @code{#f}, the value of the

								@code{%guile-for-build} fluid is used instead.


								See the @code{derivation} procedure for the meaning of

								@var{references-graphs}, @var{allowed-references}, and @var{local-build?}.

								@end deffn


								@noindent

								Here's an example of a single-output derivation that creates a directory

								containing one file:


								@lisp

								(let ((builder '(let ((out (assoc-ref %outputs "out")))

								                  (mkdir out)    ; create /gnu/store/@dots{}-goo

								                  (call-with-output-file (string-append out "/test")

								                    (lambda (p)

								                      (display '(hello guix) p))))))

								  (build-expression->derivation store "goo" builder))


								@result{} #<derivation /gnu/store/@dots{}-goo.drv => @dots{}>

								@end lisp


								@node The Store Monad

								@section The Store Monad


								@cindex 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.


								@cindex monadic values

								@cindex monadic functions

								This is where the @code{(guix monads)} module comes in.  This module

								provides a framework for working with @dfn{monads}, and a particularly

								useful monad for our uses, the @dfn{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

								@dfn{monadic values}; procedures that return such values are called

								@dfn{monadic procedures}.


								Consider this ``normal'' procedure:


								@example

								(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))))

								@end example


								Using @code{(guix monads)} and @code{(guix gexp)}, it may be rewritten

								as a monadic function:


								@example

								(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))))

								@end example


								There several things to note in the second version: the @code{store}

								parameter is now implicit and is ``threaded'' in the calls to the

								@code{package->derivation} and @code{gexp->derivation} monadic

								procedures, and the monadic value returned by @code{package->derivation}

								is @dfn{bound} using @code{mlet} instead of plain @code{let}.


								As it turns out, the call to @code{package->derivation} can even be

								omitted since it will take place implicitly, as we will see later

								(@pxref{G-Expressions}):


								@example

								(define (sh-symlink)

								  (gexp->derivation "sh"

								                    #~(symlink (string-append #$bash "/bin/bash")

								                               #$output)))

								@end example


								Calling the monadic @code{sh-symlink} has no effect.  To get the desired

								effect, one must use @code{run-with-store}:


								@example

								(run-with-store (open-connection) (sh-symlink))

								@result{} /gnu/store/...-sh-symlink

								@end example


								Note that the @code{(guix monad-repl)} module extends Guile's REPL with

								new ``meta-commands'' to make it easier to deal with monadic procedures:

								@code{run-in-store}, and @code{enter-store-monad}.  The former, is used

								to ``run'' a single monadic value through the store:


								@example

								scheme@@(guile-user)> ,run-in-store (package->derivation hello)

								$1 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>

								@end example


								The latter enters a recursive REPL, where all the return values are

								automatically run through the store:


								@example

								scheme@@(guile-user)> ,enter-store-monad

								store-monad@@(guile-user) [1]> (package->derivation hello)

								$2 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>

								store-monad@@(guile-user) [1]> (text-file "foo" "Hello!")

								$3 = "/gnu/store/@dots{}-foo"

								store-monad@@(guile-user) [1]> ,q

								scheme@@(guile-user)>

								@end example


								@noindent

								Note that non-monadic values cannot be returned in the

								@code{store-monad} REPL.


								The main syntactic forms to deal with monads in general are provided by

								the @code{(guix monads)} module and are described below.


								@deffn {Scheme Syntax} with-monad @var{monad} @var{body} ...

								Evaluate any @code{>>=} or @code{return} forms in @var{body} as being

								in @var{monad}.

								@end deffn


								@deffn {Scheme Syntax} return @var{val}

								Return a monadic value that encapsulates @var{val}.

								@end deffn


								@deffn {Scheme Syntax} >>= @var{mval} @var{mproc} ...

								@dfn{Bind} monadic value @var{mval}, passing its ``contents'' to monadic

								procedures @var{mproc}@dots{}@footnote{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 @var{mproc} or several of them, as

								in this example:


								@example

								(run-with-state

								    (with-monad %state-monad

								      (>>= (return 1)

								           (lambda (x) (return (+ 1 x)))

								           (lambda (x) (return (* 2 x)))))

								  'some-state)


								@result{} 4

								@result{} some-state

								@end example

								@end deffn


								@deffn {Scheme Syntax} mlet @var{monad} ((@var{var} @var{mval}) ...) @

								       @var{body} ...

								@deffnx {Scheme Syntax} mlet* @var{monad} ((@var{var} @var{mval}) ...) @

								       @var{body} ...

								Bind the variables @var{var} to the monadic values @var{mval} in

								@var{body}.  The form (@var{var} -> @var{val}) binds @var{var} to the

								``normal'' value @var{val}, as per @code{let}.


								@code{mlet*} is to @code{mlet} what @code{let*} is to @code{let}

								(@pxref{Local Bindings,,, guile, GNU Guile Reference Manual}).

								@end deffn


								@deffn {Scheme System} mbegin @var{monad} @var{mexp} ...

								Bind @var{mexp} and the following monadic expressions in sequence,

								returning the result of the last expression.


								This is akin to @code{mlet}, except that the return values of the

								monadic expressions are ignored.  In that sense, it is analogous to

								@code{begin}, but applied to monadic expressions.

								@end deffn


								@cindex state monad

								The @code{(guix monads)} module provides the @dfn{state monad}, which

								allows an additional value---the state---to be @emph{threaded} through

								monadic procedure calls.


								@defvr {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 @code{square} procedure returns a value

								in the state monad.  It returns the square of its argument, but also

								increments the current state value:


								@example

								(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)

								@result{} (0 1 4)

								@result{} 3

								@end example


								When ``run'' through @var{%state-monad}, we obtain that additional state

								value, which is the number of @code{square} calls.

								@end defvr


								@deffn {Monadic Procedure} current-state

								Return the current state as a monadic value.

								@end deffn


								@deffn {Monadic Procedure} set-current-state @var{value}

								Set the current state to @var{value} and return the previous state as a

								monadic value.

								@end deffn


								@deffn {Monadic Procedure} state-push @var{value}

								Push @var{value} to the current state, which is assumed to be a list,

								and return the previous state as a monadic value.

								@end deffn


								@deffn {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.

								@end deffn


								@deffn {Scheme Procedure} run-with-state @var{mval} [@var{state}]

								Run monadic value @var{mval} starting with @var{state} as the initial

								state.  Return two values: the resulting value, and the resulting state.

								@end deffn


								The main interface to the store monad, provided by the @code{(guix

								store)} module, is as follows.


								@defvr {Scheme Variable} %store-monad

								The store monad---an alias for @var{%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 @code{run-with-store} procedure (see below.)

								@end defvr


								@deffn {Scheme Procedure} run-with-store @var{store} @var{mval} [#:guile-for-build] [#:system (%current-system)]

								Run @var{mval}, a monadic value in the store monad, in @var{store}, an

								open store connection.

								@end deffn


								@deffn {Monadic Procedure} text-file @var{name} @var{text} [@var{references}]

								Return as a monadic value the absolute file name in the store of the file

								containing @var{text}, a string.  @var{references} is a list of store items that the

								resulting text file refers to; it defaults to the empty list.

								@end deffn


								@deffn {Monadic Procedure} interned-file @var{file} [@var{name}] @

								         [#:recursive? #t]

								Return the name of @var{file} once interned in the store.  Use

								@var{name} as its store name, or the basename of @var{file} if

								@var{name} is omitted.


								When @var{recursive?} is true, the contents of @var{file} are added

								recursively; if @var{file} designates a flat file and @var{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:


								@example

								(run-with-store (open-connection)

								  (mlet %store-monad ((a (interned-file "README"))

								                      (b (interned-file "README" "LEGU-MIN")))

								    (return (list a b))))


								@result{} ("/gnu/store/rwm@dots{}-README" "/gnu/store/44i@dots{}-LEGU-MIN")

								@end example


								@end deffn


								The @code{(guix packages)} module exports the following package-related

								monadic procedures:


								@deffn {Monadic Procedure} package-file @var{package} [@var{file}] @

								       [#:system (%current-system)] [#:target #f] @

								       [#:output "out"] Return as a monadic

								value in the absolute file name of @var{file} within the @var{output}

								directory of @var{package}.  When @var{file} is omitted, return the name

								of the @var{output} directory of @var{package}.  When @var{target} is

								true, use it as a cross-compilation target triplet.

								@end deffn


								@deffn {Monadic Procedure} package->derivation @var{package} [@var{system}]

								@deffnx {Monadic Procedure} package->cross-derivation @var{package} @

								          @var{target} [@var{system}]

								Monadic version of @code{package-derivation} and

								@code{package-cross-derivation} (@pxref{Defining Packages}).

								@end deffn


								@node G-Expressions

								@section G-Expressions


								@cindex G-expression

								@cindex build code quoting

								So we have ``derivations'', which represent a sequence of build actions

								to be performed to produce an item in the store (@pxref{Derivations}).

								Those build actions are performed when asking the daemon to actually

								build the derivations; they are run by the daemon in a container

								(@pxref{Invoking guix-daemon}).


								@cindex strata of code

								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 @dfn{strata} of Scheme

								code@footnote{The term @dfn{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

								@url{http://okmij.org/ftp/meta-programming/#meta-scheme, essays and code

								on this topic}, refers to this kind of code generation as

								@dfn{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

								@command{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 @code{quasiquote} mechanism to construct build

								expressions.


								The @code{(guix gexp)} module implements @dfn{G-expressions}, a form of

								S-expressions adapted to build expressions.  G-expressions, or

								@dfn{gexps}, consist essentially in three syntactic forms: @code{gexp},

								@code{ungexp}, and @code{ungexp-splicing} (or simply: @code{#~},

								@code{#$}, and @code{#$@@}), which are comparable respectively to

								@code{quasiquote}, @code{unquote}, and @code{unquote-splicing}

								(@pxref{Expression Syntax, @code{quasiquote},, guile, GNU Guile

								Reference Manual}).  However, there are major differences:


								@itemize

								@item

								Gexps are meant to be written to a file and run or manipulated by other

								processes.


								@item

								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.


								@item

								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.

								@end itemize


								This mechanism is not limited to package and derivation

								objects: @dfn{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 @code{local-file} and @code{plain-file}

								below.)


								To illustrate the idea, here is an example of a gexp:


								@example

								(define build-exp

								  #~(begin

								      (mkdir #$output)

								      (chdir #$output)

								      (symlink (string-append #$coreutils "/bin/ls")

								               "list-files")))

								@end example


								This gexp can be passed to @code{gexp->derivation}; we obtain a

								derivation that builds a directory containing exactly one symlink to

								@file{/gnu/store/@dots{}-coreutils-8.22/bin/ls}:


								@example

								(gexp->derivation "the-thing" build-exp)

								@end example


								As one would expect, the @code{"/gnu/store/@dots{}-coreutils-8.22"} string is

								substituted to the reference to the @var{coreutils} package in the

								actual build code, and @var{coreutils} is automatically made an input to

								the derivation.  Likewise, @code{#$output} (equivalent to @code{(ungexp

								output)}) is replaced by a string containing the derivation's output

								directory name.


								@cindex cross compilation

								In a cross-compilation context, it is useful to distinguish between

								references to the @emph{native} build of a package---that can run on the

								host---versus references to cross builds of a package.  To that end, the

								@code{#+} plays the same role as @code{#$}, but is a reference to a

								native package build:


								@example

								(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")

								@end example


								@noindent

								In the example above, the native build of @var{coreutils} is used, so

								that @command{ln} can actually run on the host; but then the

								cross-compiled build of @var{emacs} is referenced.


								The syntactic form to construct gexps is summarized below.


								@deffn {Scheme Syntax} #~@var{exp}

								@deffnx {Scheme Syntax} (gexp @var{exp})

								Return a G-expression containing @var{exp}.  @var{exp} may contain one

								or more of the following forms:


								@table @code

								@item #$@var{obj}

								@itemx (ungexp @var{obj})

								Introduce a reference to @var{obj}.  @var{obj} may have one of the

								supported types, for example a package or a

								derivation, in which case the @code{ungexp} form is replaced by its

								output file name---e.g., @code{"/gnu/store/@dots{}-coreutils-8.22}.


								If @var{obj} is a list, it is traversed and references to supported

								objects are substituted similarly.


								If @var{obj} is another gexp, its contents are inserted and its

								dependencies are added to those of the containing gexp.


								If @var{obj} is another kind of object, it is inserted as is.


								@item #$@var{obj}:@var{output}

								@itemx (ungexp @var{obj} @var{output})

								This is like the form above, but referring explicitly to the

								@var{output} of @var{obj}---this is useful when @var{obj} produces

								multiple outputs (@pxref{Packages with Multiple Outputs}).


								@item #+@var{obj}

								@itemx #+@var{obj}:output

								@itemx (ungexp-native @var{obj})

								@itemx (ungexp-native @var{obj} @var{output})

								Same as @code{ungexp}, but produces a reference to the @emph{native}

								build of @var{obj} when used in a cross compilation context.


								@item #$output[:@var{output}]

								@itemx (ungexp output [@var{output}])

								Insert a reference to derivation output @var{output}, or to the main

								output when @var{output} is omitted.


								This only makes sense for gexps passed to @code{gexp->derivation}.


								@item #$@@@var{lst}

								@itemx (ungexp-splicing @var{lst})

								Like the above, but splices the contents of @var{lst} inside the

								containing list.


								@item #+@@@var{lst}

								@itemx (ungexp-native-splicing @var{lst})

								Like the above, but refers to native builds of the objects listed in

								@var{lst}.


								@end table


								G-expressions created by @code{gexp} or @code{#~} are run-time objects

								of the @code{gexp?} type (see below.)

								@end deffn


								@deffn {Scheme Procedure} gexp? @var{obj}

								Return @code{#t} if @var{obj} is a G-expression.

								@end deffn


								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 (@pxref{The Store Monad}, for more

								information about monads.)


								@deffn {Monadic Procedure} gexp->derivation @var{name} @var{exp} @

								       [#:system (%current-system)] [#:target #f] [#:graft? #t] @

								       [#:hash #f] [#:hash-algo #f] @

								       [#:recursive? #f] [#:env-vars '()] [#:modules '()] @

								       [#:module-path @var{%load-path}] @

								       [#:references-graphs #f] [#:allowed-references #f] @

								       [#:leaked-env-vars #f] @

								       [#:local-build? #f] [#:guile-for-build #f]

								Return a derivation @var{name} that runs @var{exp} (a gexp) with

								@var{guile-for-build} (a derivation) on @var{system}.  When @var{target}

								is true, it is used as the cross-compilation target triplet for packages

								referred to by @var{exp}.


								Make @var{modules} available in the evaluation context of @var{exp};

								@var{modules} is a list of names of Guile modules searched in

								@var{module-path} to be copied in the store, compiled, and made available in

								the load path during the execution of @var{exp}---e.g., @code{((guix

								build utils) (guix build gnu-build-system))}.


								@var{graft?} determines whether packages referred to by @var{exp} should be grafted when

								applicable.


								When @var{references-graphs} is true, it must be a list of tuples of one of the

								following forms:


								@example

								(@var{file-name} @var{package})

								(@var{file-name} @var{package} @var{output})

								(@var{file-name} @var{derivation})

								(@var{file-name} @var{derivation} @var{output})

								(@var{file-name} @var{store-item})

								@end example


								The right-hand-side of each element of @var{references-graphs} is automatically made

								an input of the build process of @var{exp}.  In the build environment, each

								@var{file-name} contains the reference graph of the corresponding item, in a simple

								text format.


								@var{allowed-references} must be either @code{#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 @code{derivation} (@pxref{Derivations}).

								@end deffn


								@cindex file-like objects

								The @code{local-file} and @code{plain-file} procedures below return

								@dfn{file-like objects}.  That is, when unquoted in a G-expression,

								these objects lead to a file in the store.  Consider this G-expression:


								@example

								#~(system* (string-append #$glibc "/sbin/nscd") "-f"

								           #$(local-file "/tmp/my-nscd.conf"))

								@end example


								The effect here is to ``intern'' @file{/tmp/my-nscd.conf} by copying it

								to the store.  Once expanded, for instance @i{via}

								@code{gexp->derivation}, the G-expression refers to that copy under

								@file{/gnu/store}; thus, modifying or removing the file in @file{/tmp}

								does not have any effect on what the G-expression does.

								@code{plain-file} can be used similarly; it differs in that the file

								content is directly passed as a string.


								@deffn {Scheme Procedure} local-file @var{file} [@var{name}] @

								   [#:recursive? #t]

								Return an object representing local file @var{file} to add to the store; this

								object can be used in a gexp.  @var{file} will be added to the store under @var{name}--by

								default the base name of @var{file}.


								When @var{recursive?} is true, the contents of @var{file} are added recursively; if @var{file}

								designates a flat file and @var{recursive?} is true, its contents are added, and its

								permission bits are kept.


								This is the declarative counterpart of the @code{interned-file} monadic

								procedure (@pxref{The Store Monad, @code{interned-file}}).

								@end deffn


								@deffn {Scheme Procedure} plain-file @var{name} @var{content}

								Return an object representing a text file called @var{name} with the given

								@var{content} (a string) to be added to the store.


								This is the declarative counterpart of @code{text-file}.

								@end deffn


								@deffn {Monadic Procedure} gexp->script @var{name} @var{exp}

								Return an executable script @var{name} that runs @var{exp} using

								@var{guile} with @var{modules} in its search path.


								The example below builds a script that simply invokes the @command{ls}

								command:


								@example

								(use-modules (guix gexp) (gnu packages base))


								(gexp->script "list-files"

								              #~(execl (string-append #$coreutils "/bin/ls")

								                       "ls"))

								@end example


								When ``running'' it through the store (@pxref{The Store Monad,

								@code{run-with-store}}), we obtain a derivation that produces an

								executable file @file{/gnu/store/@dots{}-list-files} along these lines:


								@example

								#!/gnu/store/@dots{}-guile-2.0.11/bin/guile -ds

								!#

								(execl (string-append "/gnu/store/@dots{}-coreutils-8.22"/bin/ls")

								       "ls")

								@end example

								@end deffn


								@deffn {Monadic Procedure} gexp->file @var{name} @var{exp}

								Return a derivation that builds a file @var{name} containing @var{exp}.


								The resulting file holds references to all the dependencies of @var{exp}

								or a subset thereof.

								@end deffn


								@deffn {Monadic Procedure} text-file* @var{name} @var{text} @dots{}

								Return as a monadic value a derivation that builds a text file

								containing all of @var{text}.  @var{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 @code{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:


								@example

								(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"))

								@end example


								In this example, the resulting @file{/gnu/store/@dots{}-profile.sh} file

								will references @var{coreutils}, @var{grep}, and @var{sed}, thereby

								preventing them from being garbage-collected during its lifetime.

								@end deffn


								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

								@code{(guix build @dots{})} name space.


								@c *********************************************************************

								@node Utilities

								@chapter 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.


								@menu

								* Invoking guix build::         Building packages from the command line.

								* Invoking guix download::      Downloading a file and printing its hash.

								* Invoking guix hash::          Computing the cryptographic hash of a file.

								* Invoking guix import::        Importing package definitions.

								* Invoking guix refresh::       Updating package definitions.

								* Invoking guix lint::          Finding errors in package definitions.

								* Invoking guix environment::   Setting up development environments.

								* Invoking guix publish::       Sharing substitutes.

								@end menu


								@node Invoking guix build

								@section Invoking @command{guix build}


								The @command{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

								@command{guix package} command (@pxref{Invoking guix package}).  Thus,

								it is mainly useful for distribution developers.


								The general syntax is:


								@example

								guix build @var{options} @var{package-or-derivation}@dots{}

								@end example


								@var{package-or-derivation} may be either the name of a package found in

								the software distribution such as @code{coreutils} or

								@code{coreutils-8.20}, or a derivation such as

								@file{/gnu/store/@dots{}-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 (@pxref{Package Modules}).


								Alternatively, the @code{--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 @var{options} may be zero or more of the following:


								@table @code


								@item --expression=@var{expr}

								@itemx -e @var{expr}

								Build the package or derivation @var{expr} evaluates to.


								For example, @var{expr} may be @code{(@@ (gnu packages guile)

								guile-1.8)}, which unambiguously designates this specific variant of

								version 1.8 of Guile.


								Alternately, @var{expr} may be a G-expression, in which case it is used

								as a build program passed to @code{gexp->derivation}

								(@pxref{G-Expressions}).


								Lastly, @var{expr} may refer to a zero-argument monadic procedure

								(@pxref{The Store Monad}).  The procedure must return a derivation as a

								monadic value, which is then passed through @code{run-with-store}.


								@item --source

								@itemx -S

								Build the packages' source derivations, rather than the packages

								themselves.


								For instance, @code{guix build -S gcc} returns something like

								@file{/gnu/store/@dots{}-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 @code{origin} (@pxref{Defining

								Packages}).


								@item --sources

								Fetch and return the source of @var{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 @var{packages}, allowing you to

								eventually build them even without network access.  It is an extension

								of the @code{--source} option and can accept one of the following

								optional argument values:


								@table @code

								@item package

								This value causes the @code{--sources} option to behave in the same way

								as the @code{--source} option.


								@item all

								Build all packages' source derivations, including any source that might

								be listed as @code{inputs}.  This is the default value.


								@example

								$ guix build --sources tzdata

								The following derivations will be built:

								   /gnu/store/@dots{}-tzdata2015b.tar.gz.drv

								   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv

								@end example


								@item 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.


								@example

								$ guix build --sources=transitive tzdata

								The following derivations will be built:

								   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv

								   /gnu/store/@dots{}-findutils-4.4.2.tar.xz.drv

								   /gnu/store/@dots{}-grep-2.21.tar.xz.drv

								   /gnu/store/@dots{}-coreutils-8.23.tar.xz.drv

								   /gnu/store/@dots{}-make-4.1.tar.xz.drv

								   /gnu/store/@dots{}-bash-4.3.tar.xz.drv

								@dots{}

								@end example


								@end table


								@item --system=@var{system}

								@itemx -s @var{system}

								Attempt to build for @var{system}---e.g., @code{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

								@code{--system=i686-linux} on an @code{x86_64-linux} system allows users

								to build packages in a complete 32-bit environment.


								@item --target=@var{triplet}

								@cindex cross-compilation

								Cross-build for @var{triplet}, which must be a valid GNU triplet, such

								as @code{"mips64el-linux-gnu"} (@pxref{Configuration Names, GNU

								configuration triplets,, configure, GNU Configure and Build System}).


								@item --with-source=@var{source}

								Use @var{source} as the source of the corresponding package.

								@var{source} must be a file name or a URL, as for @command{guix

								download} (@pxref{Invoking guix download}).


								The ``corresponding package'' is taken to be one specified on the

								command line whose name matches the base of @var{source}---e.g., if

								@var{source} is @code{/src/guile-2.0.10.tar.gz}, the corresponding

								package is @code{guile}.  Likewise, the version string is inferred from

								@var{source}; in the previous example, it's @code{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

								@file{ed-1.7.tar.gz} from a GNU mirror and uses that as the source for

								the @code{ed} package:


								@example

								guix build ed --with-source=mirror://gnu/ed/ed-1.7.tar.gz

								@end example


								As a developer, @code{--with-source} makes it easy to test release

								candidates:


								@example

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

								@end example


								@dots{} or to build from a checkout in a pristine environment:


								@example

								$ git clone git://git.sv.gnu.org/guix.git

								$ guix build guix --with-source=./guix

								@end example


								@item --no-grafts

								Do not ``graft'' packages.  In practice, this means that package updates

								available as grafts are not applied.  @xref{Security Updates}, for more

								information on grafts.


								@item --derivations

								@itemx -d

								Return the derivation paths, not the output paths, of the given

								packages.


								@item --root=@var{file}

								@itemx -r @var{file}

								Make @var{file} a symlink to the result, and register it as a garbage

								collector root.


								@item --log-file

								Return the build log file names for the given

								@var{package-or-derivation}s, 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:


								@example

								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)'

								@end example


								@end table


								@cindex common build options

								In addition, a number of options that control the build process are

								common to @command{guix build} and other commands that can spawn builds,

								such as @command{guix package} or @command{guix archive}.  These are the

								following:


								@table @code


								@item --load-path=@var{directory}

								@itemx -L @var{directory}

								Add @var{directory} to the front of the package module search path

								(@pxref{Package Modules}).


								This allows users to define their own packages and make them visible to

								the command-line tools.


								@item --keep-failed

								@itemx -K

								Keep the build tree of failed builds.  Thus, if a build fail, its build

								tree is kept under @file{/tmp}, in a directory whose name is shown at

								the end of the build log.  This is useful when debugging build issues.


								@item --dry-run

								@itemx -n

								Do not build the derivations.


								@item --fallback

								When substituting a pre-built binary fails, fall back to building

								packages locally.


								@item --no-substitutes

								Do not use substitutes for build products.  That is, always build things

								locally instead of allowing downloads of pre-built binaries

								(@pxref{Substitutes}).


								@item --no-build-hook

								Do not attempt to offload builds @i{via} the daemon's ``build hook''

								(@pxref{Daemon Offload Setup}).  That is, always build things locally

								instead of offloading builds to remote machines.


								@item --max-silent-time=@var{seconds}

								When the build or substitution process remains silent for more than

								@var{seconds}, terminate it and report a build failure.


								@item --timeout=@var{seconds}

								Likewise, when the build or substitution process lasts for more than

								@var{seconds}, terminate it and report a build failure.


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

								@code{--timeout=0}.


								@item --verbosity=@var{level}

								Use the given verbosity level.  @var{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.


								@item --cores=@var{n}

								@itemx -c @var{n}

								Allow the use of up to @var{n} CPU cores for the build.  The special

								value @code{0} means to use as many CPU cores as available.


								@item --max-jobs=@var{n}

								@itemx -M @var{n}

								Allow at most @var{n} build jobs in parallel.  @xref{Invoking

								guix-daemon, @code{--max-jobs}}, for details about this option and the

								equivalent @command{guix-daemon} option.


								@end table


								Behind the scenes, @command{guix build} is essentially an interface to

								the @code{package-derivation} procedure of the @code{(guix packages)}

								module, and to the @code{build-derivations} procedure of the @code{(guix

								derivations)} module.


								In addition to options explicitly passed on the command line,

								@command{guix build} and other @command{guix} commands that support

								building honor the @code{GUIX_BUILD_OPTIONS} environment variable.


								@defvr {Environment Variable} GUIX_BUILD_OPTIONS

								Users can define this variable to a list of command line options that

								will automatically be used by @command{guix build} and other

								@command{guix} commands that can perform builds, as in the example

								below:


								@example

								$ export GUIX_BUILD_OPTIONS="--no-substitutes -c 2 -L /foo/bar"

								@end example


								These options are parsed independently, and the result is appended to

								the parsed command-line options.

								@end defvr


								@node Invoking guix download

								@section Invoking @command{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 (@pxref{Defining Packages}).  The

								@command{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 @command{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 (@pxref{Invoking guix gc}).


								The @command{guix download} command supports the same URIs as used in

								package definitions.  In particular, it supports @code{mirror://} URIs.

								@code{https} URIs (HTTP over TLS) are supported @emph{provided} the

								Guile bindings for GnuTLS are available in the user's environment; when

								they are not available, an error is raised.  @xref{Guile Preparations,

								how to install the GnuTLS bindings for Guile,, gnutls-guile,

								GnuTLS-Guile}, for more information.


								The following option is available:


								@table @code

								@item --format=@var{fmt}

								@itemx -f @var{fmt}

								Write the hash in the format specified by @var{fmt}.  For more

								information on the valid values for @var{fmt}, @pxref{Invoking guix hash}.

								@end table


								@node Invoking guix hash

								@section Invoking @command{guix hash}


								The @command{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 (@pxref{Defining Packages}).


								The general syntax is:


								@example

								guix hash @var{option} @var{file}

								@end example


								@command{guix hash} has the following option:


								@table @code


								@item --format=@var{fmt}

								@itemx -f @var{fmt}

								Write the hash in the format specified by @var{fmt}.


								Supported formats: @code{nix-base32}, @code{base32}, @code{base16}

								(@code{hex} and @code{hexadecimal} can be used as well).


								If the @option{--format} option is not specified, @command{guix hash}

								will output the hash in @code{nix-base32}.  This representation is used

								in the definitions of packages.


								@item --recursive