guix.texi

meant to be used in the build stratum, these modules are kept in the
@code{(guix build @dots{})} name space.

@cindex lowering, of high-level objects in gexps
Internally, high-level objects are @dfn{lowered}, using their compiler,
to either derivations or store items.  For instance, lowering a package
yields a derivation, and lowering a @code{plain-file} yields a store
item.  This is achieved using the @code{lower-object} monadic procedure.

@deffn {Monadic Procedure} lower-object @var{obj} [@var{system}] @
           [#:target #f]
Return as a value in @var{%store-monad} the derivation or store item
corresponding to @var{obj} for @var{system}, cross-compiling for
@var{target} if @var{target} is true.  @var{obj} must be an object that
has an associated gexp compiler, such as a @code{<package>}.
@end deffn


@c *********************************************************************
@node Utilities
@chapter Utilities

This section describes Guix command-line utilities.  Some of them are
primarily targeted at developers and users who write new package
definitions, while others are more generally useful.  They complement
the Scheme programming interface of Guix in a convenient way.

@menu
* Invoking guix build::         Building packages from the command line.
* Invoking guix edit::          Editing package definitions.
* 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 size::          Profiling disk usage.
* Invoking guix graph::         Visualizing the graph of packages.
* Invoking guix environment::   Setting up development environments.
* Invoking guix publish::       Sharing substitutes.
* Invoking guix challenge::     Challenging substitute servers.
* Invoking guix container::     Process isolation.
@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

As an example, the following command builds the latest versions of Emacs
and of Guile, displays their build logs, and finally displays the
resulting directories:

@example
guix build emacs guile
@end example

Similarly, the following command builds all the available packages:

@example
guix build --quiet --keep-going \
  `guix package -A | cut -f1,2 --output-delimiter=@@`
@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
disambiguating among several same-named packages or package variants is
needed.

There may be zero or more @var{options}.  The available options are
described in the subsections below.

@menu
* Common Build Options::        Build options for most commands.
* Package Transformation Options::    Creating variants of packages.
* Additional Build Options::    Options specific to 'guix build'.
@end menu

@node Common Build Options
@subsection Common Build Options

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 fails, 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 --keep-going
@itemx -k
Keep going when some of the derivations fail to build; return only once
all the builds have either completed or failed.

The default behavior is to stop as soon as one of the specified
derivations has failed.

@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 --substitute-urls=@var{urls}
@anchor{client-substitute-urls}
Consider @var{urls} the whitespace-separated list of substitute source
URLs, overriding the default list of URLs of @command{guix-daemon}
(@pxref{daemon-substitute-urls,, @command{guix-daemon} URLs}).

This means that substitutes may be downloaded from @var{urls}, provided
they are signed by a key authorized by the system administrator
(@pxref{Substitutes}).

When @var{urls} is the empty string, substitutes are effectively
disabled.

@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-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 --rounds=@var{n}
Build each derivation @var{n} times in a row, and raise an error if
consecutive build results are not bit-for-bit identical.

This is a useful way to detect non-deterministic builds processes.
Non-deterministic build processes are a problem because they make it
practically impossible for users to @emph{verify} whether third-party
binaries are genuine.  @xref{Invoking guix challenge}, for more.

Note that, currently, the differing build results are not kept around,
so you will have to manually investigate in case of an error---e.g., by
stashing one of the build results with @code{guix archive --export}
(@pxref{Invoking guix archive}), then rebuilding, and finally comparing
the two results.

@item --no-build-hook
Do not attempt to offload builds @i{via} the ``build hook'' of the daemon
(@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 Package Transformation Options
@subsection Package Transformation Options

@cindex package variants
Another set of command-line options supported by @command{guix build}
and also @command{guix package} are @dfn{package transformation
options}.  These are options that make it possible to define @dfn{package
variants}---for instance, packages built from different source code.
This is a convenient way to create customized packages on the fly
without having to type in the definitions of package variants
(@pxref{Defining Packages}).

@table @code

@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 the one specified on the
command line the name of which 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 is @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 --with-input=@var{package}=@var{replacement}
Replace dependency on @var{package} by a dependency on
@var{replacement}.  @var{package} must be a package name, and
@var{replacement} must be a package specification such as @code{guile}
or @code{guile@@1.8}.

For instance, the following command builds Guix, but replaces its
dependency on the current stable version of Guile with a dependency on
the development version of Guile, @code{guile-next}:

@example
guix build --with-input=guile=guile-next guix
@end example

This is a recursive, deep replacement.  So in this example, both
@code{guix} and its dependency @code{guile-json} (which also depends on
@code{guile}) get rebuilt against @code{guile-next}.

However, implicit inputs are left unchanged.
@end table

@node Additional Build Options
@subsection Additional Build Options

The command-line options presented below are specific to @command{guix
build}.

@table @code

@item --quiet
@itemx -q
Build quietly, without displaying the build log.  Upon completion, the
build log is kept in @file{/var} (or similar) and can always be
retrieved using the @option{--log-file} option.

@item --file=@var{file}
@itemx -f @var{file}

Build the package or derivation that the code within @var{file}
evaluates to.

As an example, @var{file} might contain a package definition like this
(@pxref{Defining Packages}):

@example
@verbatiminclude package-hello.scm
@end example

@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.

Alternatively, @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 source derivations of the packages, 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 the GCC
source tarball.

The returned source tarball is the result of applying any patches and
code snippets specified in the package @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 the source derivations of all packages, 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 the source derivations of all packages, as well of all transitive
inputs to the packages.  This can be used e.g. to
prefetch package source for later offline building.

@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 system type of the build host.

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}).

@anchor{build-check}
@item --check
@cindex determinism, checking
@cindex reproducibility, checking
Rebuild @var{package-or-derivation}, which are already available in the
store, and raise an error if the build results are not bit-for-bit
identical.

This mechanism allows you to check whether previously installed
substitutes are genuine (@pxref{Substitutes}), or whether the build result
of a package is deterministic.  @xref{Invoking guix challenge}, for more
background information and tools.

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

@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 or URLs for the given
@var{package-or-derivation}, or raise an error if build logs are
missing.

This works regardless of how packages or derivations are specified.  For
instance, the following invocations are equivalent:

@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

If a log is unavailable locally, and unless @code{--no-substitutes} is
passed, the command looks for a corresponding log on one of the
substitute servers (as specified with @code{--substitute-urls}.)

So for instance, imagine you want to see the build log of GDB on MIPS,
but you are actually on an @code{x86_64} machine:

@example
$ guix build --log-file gdb -s mips64el-linux
https://hydra.gnu.org/log/@dots{}-gdb-7.10
@end example

You can freely access a huge library of build logs!
@end table


@node Invoking guix edit
@section Invoking @command{guix edit}

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

@example
guix edit gcc@@4.9 vim
@end example

@noindent
launches the program specified in the @code{VISUAL} or in the
@code{EDITOR} environment variable to edit the recipe of GCC@tie{}4.9.3
and that of Vim.

If you are using Emacs, note that the Emacs user interface provides the
@kbd{M-x guix-edit} command and a similar functionality in the ``package
info'' and ``package list'' buffers created by the @kbd{M-x
guix-search-by-name} and similar commands (@pxref{Emacs Commands}).


@node Invoking guix download
@section Invoking @command{guix download}

When writing a package definition, developers typically need to download
a source tarball, compute its SHA256 hash, and write that
hash in the package definition (@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
@itemx -r
Compute the hash on @var{file} recursively.

In this case, the hash is computed on an archive containing @var{file},
including its children if it is a directory.  Some of the metadata of
@var{file} is part of the archive; for instance, when @var{file} is a
regular file, the hash is different depending on whether @var{file} is
executable or not.  Metadata such as time stamps has no impact on the
hash (@pxref{Invoking guix archive}).
@c FIXME: Replace xref above with xref to an ``Archive'' section when
@c it exists.

@end table

@node Invoking guix import
@section Invoking @command{guix import}

@cindex importing packages
@cindex package import
@cindex package conversion
The @command{guix import} command is useful for people who would like to
add a package to the distribution with as little work as
possible---a legitimate demand.  The command knows of a few
repositories from which it can ``import'' package metadata.  The result
is a package definition, or a template thereof, in the format we know
(@pxref{Defining Packages}).

The general syntax is:

@example
guix import @var{importer} @var{options}@dots{}
@end example

@var{importer} specifies the source from which to import package
metadata, and @var{options} specifies a package identifier and other
options specific to @var{importer}.  Currently, the available
``importers'' are:

@table @code
@item gnu
Import metadata for the given GNU package.  This provides a template
for the latest version of that GNU package, including the hash of its
source tarball, and its canonical synopsis and description.

Additional information such as the package dependencies and its
license needs to be figured out manually.

For example, the following command returns a package definition for
GNU@tie{}Hello:

@example
guix import gnu hello
@end example

Specific command-line options are:

@table @code
@item --key-download=@var{policy}
As for @code{guix refresh}, specify the policy to handle missing OpenPGP
keys when verifying the package signature.  @xref{Invoking guix
refresh, @code{--key-download}}.
@end table

@item pypi
@cindex pypi
Import metadata from the @uref{https://pypi.python.org/, Python Package
Index}@footnote{This functionality requires Guile-JSON to be installed.
@xref{Requirements}.}.  Information is taken from the JSON-formatted
description available at @code{pypi.python.org} and usually includes all
the relevant information, including package dependencies.  For maximum
efficiency, it is recommended to install the @command{unzip} utility, so
that the importer can unzip Python wheels and gather data from them.

The command below imports metadata for the @code{itsdangerous} Python
package:

@example
guix import pypi itsdangerous
@end example

@item gem
@cindex gem
Import metadata from @uref{https://rubygems.org/,
RubyGems}@footnote{This functionality requires Guile-JSON to be
installed.  @xref{Requirements}.}.  Information is taken from the
JSON-formatted description available at @code{rubygems.org} and includes
most relevant information, including runtime dependencies.  There are
some caveats, however.  The metadata doesn't distinguish between
synopses and descriptions, so the same string is used for both fields.
Additionally, the details of non-Ruby dependencies required to build
native extensions is unavailable and left as an exercise to the
packager.

The command below imports metadata for the @code{rails} Ruby package:

@example
guix import gem rails
@end example

@item cpan
@cindex CPAN
Import metadata from @uref{https://www.metacpan.org/, MetaCPAN}@footnote{This
functionality requires Guile-JSON to be installed.
@xref{Requirements}.}.
Information is taken from the JSON-formatted metadata provided through
@uref{https://api.metacpan.org/, MetaCPAN's API} and includes most
relevant information, such as module dependencies.  License information
should be checked closely.  If Perl is available in the store, then the
@code{corelist} utility will be used to filter core modules out of the
list of dependencies.

The command command below imports metadata for the @code{Acme::Boolean}
Perl module:

@example
guix import cpan Acme::Boolean
@end example

@item cran
@cindex CRAN
@cindex Bioconductor
Import metadata from @uref{http://cran.r-project.org/, CRAN}, the
central repository for the @uref{http://r-project.org, GNU@tie{}R
statistical and graphical environment}.

Information is extracted from the @code{DESCRIPTION} file of the package.

The command command below imports metadata for the @code{Cairo}
R package:

@example
guix import cran Cairo
@end example

When @code{--archive=bioconductor} is added, metadata is imported from
@uref{http://www.bioconductor.org/, Bioconductor}, a repository of R
packages for for the analysis and comprehension of high-throughput
genomic data in bioinformatics.

Information is extracted from the @code{DESCRIPTION} file of a package
published on the web interface of the Bioconductor SVN repository.

The command below imports metadata for the @code{GenomicRanges}
R package:

@example
guix import cran --archive=bioconductor GenomicRanges
@end example

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

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

Usually, you will first need to do:

@example
export NIX_REMOTE=daemon
@end example

@noindent
so that @command{nix-instantiate} does not try to open the Nix database.

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

@example
guix import nix ~/path/to/nixpkgs libreoffice
@end example

@item hackage
@cindex hackage
Import metadata from the Haskell community's central package archive
@uref{https://hackage.haskell.org/, Hackage}.  Information is taken from
Cabal files and includes all the relevant information, including package
dependencies.

Specific command-line options are:

@table @code
@item --stdin
@itemx -s
Read a Cabal file from standard input.
@item --no-test-dependencies
@itemx -t
Do not include dependencies required only by the test suites.
@item --cabal-environment=@var{alist}
@itemx -e @var{alist}
@var{alist} is a Scheme alist defining the environment in which the
Cabal conditionals are evaluated.  The accepted keys are: @code{os},
@code{arch}, @code{impl} and a string representing the name of a flag.
The value associated with a flag has to be either the symbol
@code{true} or @code{false}.  The value associated with other keys
has to conform to the Cabal file format definition.  The default value
associated with the keys @code{os}, @code{arch} and @code{impl} is
@samp{linux}, @samp{x86_64} and @samp{ghc}, respectively.
@end table

The command below imports metadata for the latest version of the
@code{HTTP} Haskell package without including test dependencies and
specifying the value of the flag @samp{network-uri} as @code{false}:

@example
guix import hackage -t -e "'((\"network-uri\" . false))" HTTP
@end example

A specific package version may optionally be specified by following the
package name by an at-sign and a version number as in the following example:

@example
guix import hackage mtl@@2.1.3.1
@end example

@item elpa
@cindex elpa
Import metadata from an Emacs Lisp Package Archive (ELPA) package
repository (@pxref{Packages,,, emacs, The GNU Emacs Manual}).

Specific command-line options are:

@table @code
@item --archive=@var{repo}
@itemx -a @var{repo}
@var{repo} identifies the archive repository from which to retrieve the
information.  Currently the supported repositories and their identifiers
are:
@itemize -
@item
@uref{http://elpa.gnu.org/packages, GNU}, selected by the @code{gnu}
identifier.  This is the default.

@item
@uref{http://stable.melpa.org/packages, MELPA-Stable}, selected by the
@code{melpa-stable} identifier.

@item
@uref{http://melpa.org/packages, MELPA}, selected by the @code{melpa}
identifier.
@end itemize
@end table
@end table

The structure of the @command{guix import} code is modular.  It would be
useful to have more importers for other package formats, and your help
is welcome here (@pxref{Contributing}).

@node Invoking guix refresh
@section Invoking @command{guix refresh}

The primary audience of the @command{guix refresh} command is developers
of the GNU software distribution.  By default, it reports any packages
provided by the distribution that are outdated compared to the latest
upstream version, like this:

@example
$ guix refresh
gnu/packages/gettext.scm:29:13: gettext would be upgraded from 0.18.1.1 to 0.18.2.1
gnu/packages/glib.scm:77:12: glib would be upgraded from 2.34.3 to 2.37.0
@end example

It does so by browsing the FTP directory of each package and determining
the highest version number of the source tarballs therein.  The command
knows how to update specific types of packages: GNU packages, ELPA
packages, etc.---see the documentation for @option{--type} below.  The
are many packages, though, for which it lacks a method to determine
whether a new upstream release is available.  However, the mechanism is
extensible, so feel free to get in touch with us to add a new method!

When passed @code{--update}, it modifies distribution source files to
update the version numbers and source tarball hashes of those package
recipes (@pxref{Defining Packages}).  This is achieved by downloading
each package's latest source tarball and its associated OpenPGP
signature, authenticating the downloaded tarball against its signature
using @command{gpg}, and finally computing its hash.  When the public
key used to sign the tarball is missing from the user's keyring, an
attempt is made to automatically retrieve it from a public key server;
when this is successful, the key is added to the user's keyring; otherwise,
@command{guix refresh} reports an error.

The following options are supported:

@table @code

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to precisely refer to a package, as in this example:

@example
guix refresh -l -e '(@@@@ (gnu packages commencement) glibc-final)'
@end example

This command lists the dependents of the ``final'' libc (essentially all
the packages.)

@item --update
@itemx -u
Update distribution source files (package recipes) in place.  This is
usually run from a checkout of the Guix source tree (@pxref{Running
Guix Before It Is Installed}):

@example
$ ./pre-inst-env guix refresh -s non-core
@end example

@xref{Defining Packages}, for more information on package definitions.

@item --select=[@var{subset}]
@itemx -s @var{subset}
Select all the packages in @var{subset}, one of @code{core} or
@code{non-core}.

The @code{core} subset refers to all the packages at the core of the
distribution---i.e., packages that are used to build ``everything
else''.  This includes GCC, libc, Binutils, Bash, etc.  Usually,
changing one of these packages in the distribution entails a rebuild of
all the others.  Thus, such updates are an inconvenience to users in
terms of build time or bandwidth used to achieve the upgrade.

The @code{non-core} subset refers to the remaining packages.  It is
typically useful in cases where an update of the core packages would be
inconvenient.

@item --type=@var{updater}
@itemx -t @var{updater}
Select only packages handled by @var{updater} (may be a comma-separated
list of updaters).  Currently, @var{updater} may be one of:

@table @code
@item gnu
the updater for GNU packages;
@item gnome
the updater for GNOME packages;
@item xorg
the updater for X.org packages;
@item elpa
the updater for @uref{http://elpa.gnu.org/, ELPA} packages;
@item cran
the updater for @uref{http://cran.r-project.org/, CRAN} packages;
@item bioconductor
the updater for @uref{http://www.bioconductor.org/, Bioconductor} R packages;
@item pypi
the updater for @uref{https://pypi.python.org, PyPI} packages.
@item gem
the updater for @uref{https://rubygems.org, RubyGems} packages.
@item github
the updater for @uref{https://github.com, GitHub} packages.
@item hackage
the updater for @uref{https://hackage.haskell.org, Hackage} packages.
@end table

For instance, the following command only checks for updates of Emacs
packages hosted at @code{elpa.gnu.org} and for updates of CRAN packages:

@example
$ guix refresh --type=elpa,cran
gnu/packages/statistics.scm:819:13: r-testthat would be upgraded from 0.10.0 to 0.11.0
gnu/packages/emacs.scm:856:13: emacs-auctex would be upgraded from 11.88.6 to 11.88.9
@end example

@end table

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

@example
$ ./pre-inst-env guix refresh -u emacs idutils gcc-4.8.4
@end example

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

When considering whether to upgrade a package, it is sometimes
convenient to know which packages would be affected by the upgrade and
should be checked for compatibility.  For this the following option may
be used when passing @command{guix refresh} one or more package names:

@table @code

@item --list-updaters
@itemx -L
List available updaters and exit (see @option{--type} above.)

@item --list-dependent
@itemx -l
List top-level dependent packages that would need to be rebuilt as a
result of upgrading one or more packages.

@end table

Be aware that the @code{--list-dependent} option only
@emph{approximates} the rebuilds that would be required as a result of
an upgrade.  More rebuilds might be required under some circumstances.

@example
$ guix refresh --list-dependent flex
Building the following 120 packages would ensure 213 dependent packages are rebuilt:
hop-2.4.0 geiser-0.4 notmuch-0.18 mu-0.9.9.5 cflow-1.4 idutils-4.6 @dots{}
@end example

The command above lists a set of packages that could be built to check
for compatibility with an upgraded @code{flex} package.

The following options can be used to customize GnuPG operation:

@table @code

@item --gpg=@var{command}
Use @var{command} as the GnuPG 2.x command.  @var{command} is searched
for in @code{$PATH}.

@item --key-download=@var{policy}
Handle missing OpenPGP keys according to @var{policy}, which may be one
of:

@table @code
@item always
Always download missing OpenPGP keys from the key server, and add them
to the user's GnuPG keyring.

@item never
Never try to download missing OpenPGP keys.  Instead just bail out.

@item interactive
When a package signed with an unknown OpenPGP key is encountered, ask
the user whether to download it or not.  This is the default behavior.
@end table

@item --key-server=@var{host}