7.1 Invoking guix shell

The purpose of guix shell is to make it easy to create one-off software environments, without changing one’s profile. It is typically used to create development environments; it is also a convenient way to run applications without “polluting” your profile.

Nota: The guix shell command was recently introduced to supersede guix environment (veja Invocando guix environment). If you are familiar with guix environment, you will notice that it is similar but also—we hope!—more convenient.

A sintaxe geral é:

guix shell [options] [package…]

The following example creates an environment containing Python and NumPy, building or downloading any missing package, and runs the python3 command in that environment:

guix shell python python-numpy -- python3

Note that it is necessary to include the main python package in this command even if it is already installed into your environment. This is so that the shell environment knows to set PYTHONPATH and other related variables. The shell environment cannot check the previously installed environment, because then it would be non-deterministic. This is true for most libraries: their corresponding language package should be included in the shell invocation.

Nota: guix shell can be also be used as a script interpreter, also known as shebang. Here is an example self-contained Python script making use of this feature:

#!/usr/bin/env -S guix shell python python-numpy -- python3
import numpy
print("This is numpy", numpy.version.version)

You may pass any guix shell option, but there’s one caveat: the Linux kernel has a limit of 127 bytes on shebang length.

Development environments can be created as in the example below, which spawns an interactive shell containing all the dependencies and environment variables needed to work on Inkscape:

guix shell --development inkscape

Exiting the shell places the user back in the original environment before guix shell was invoked. The next garbage collection (veja Invocando guix gc) may clean up packages that were installed in the environment and that are no longer used outside of it.

As an added convenience, guix shell will try to do what you mean when it is invoked interactively without any other arguments as in:

guix shell

If it finds a manifest.scm in the current working directory or any of its parents, it uses this manifest as though it was given via --manifest. Likewise, if it finds a guix.scm in the same directories, it uses it to build a development profile as though both --development and --file were present. In either case, the file will only be loaded if the directory it resides in is listed in ~/.config/guix/shell-authorized-directories. This provides an easy way to define, share, and enter development environments.

By default, the shell session or command runs in an augmented environment, where the new packages are added to search path environment variables such as PATH. You can, instead, choose to create an isolated environment containing nothing but the packages you asked for. Passing the --pure option clears environment variable definitions found in the parent environment¹⁴; passing --container goes one step further by spawning a container isolated from the rest of the system:

guix shell --container emacs gcc-toolchain

The command above spawns an interactive shell in a container where nothing but emacs, gcc-toolchain, and their dependencies is available. The container lacks network access and shares no files other than the current working directory with the surrounding environment. This is useful to prevent access to system-wide resources such as /usr/bin on foreign distros.

This --container option can also prove useful if you wish to run a security-sensitive application, such as a web browser, in an isolated environment. For example, the command below launches Ungoogled-Chromium in an isolated environment, which:

• shares network access with the host
• inherits host’s environment variables DISPLAY and XAUTHORITY
• has access to host’s authentication records from the XAUTHORITY file
• has no information about host’s current directory

guix shell --container --network --no-cwd ungoogled-chromium \
  --preserve='^XAUTHORITY$' --expose="${XAUTHORITY}" \
  --preserve='^DISPLAY$' -- chromium

guix shell defines the GUIX_ENVIRONMENT variable in the shell it spawns; its value is the file name of the profile of this environment. This allows users to, say, define a specific prompt for development environments in their .bashrc (veja Bash Startup Files em The GNU Bash Reference Manual):

if [ -n "$GUIX_ENVIRONMENT" ]
then
    export PS1="\u@\h \w [dev]\$ "
fi

... or to browse the profile:

$ ls "$GUIX_ENVIRONMENT/bin"

The available options are summarized below.

--check

Set up the environment and check whether the shell would clobber environment variables. It’s a good idea to use this option the first time you run guix shell for an interactive session to make sure your setup is correct.

For example, if the shell modifies the PATH environment variable, report it since you would get a different environment than what you asked for.

Such problems usually indicate that the shell startup files are unexpectedly modifying those environment variables. For example, if you are using Bash, make sure that environment variables are set or modified in ~/.bash_profile and not in ~/.bashrc—the former is sourced only by log-in shells. Veja Bash Startup Files em The GNU Bash Reference Manual, for details on Bash start-up files.

--development

-D

Cause guix shell to include in the environment the dependencies of the following package rather than the package itself. This can be combined with other packages. For instance, the command below starts an interactive shell containing the build-time dependencies of GNU Guile, plus Autoconf, Automake, and Libtool:

guix shell -D guile autoconf automake libtool

--expression=expr

-e expr

Create an environment for the package or list of packages that expr evaluates to.

For example, running:

guix shell -D -e '(@ (gnu packages maths) petsc-openmpi)'

starts a shell with the environment for this specific variant of the PETSc package.

Running:

guix shell -e '(@ (gnu) %base-packages)'

starts a shell with all the base system packages available.

The above commands only use the default output of the given packages. To select other outputs, two element tuples can be specified:

guix shell -e '(list (@ (gnu packages bash) bash) "include")'

Veja package->development-manifest, for information on how to write a manifest for the development environment of a package.

--file=file

-f arquivo

Create an environment containing the package or list of packages that the code within file evaluates to.

Por exemplo, arquivo pode conter uma definição como esta (veja Definindo pacotes):

(use-modules (guix)
             (gnu packages gdb)
             (gnu packages autotools)
             (gnu packages texinfo))

;; Augment the package definition of GDB with the build tools
;; needed when developing GDB (and which are not needed when
;; simply installing it.)
(package
  (inherit gdb)
  (native-inputs (modify-inputs (package-native-inputs gdb)
                   (prepend autoconf-2.69 automake texinfo))))

With the file above, you can enter a development environment for GDB by running:

guix shell -D -f gdb-devel.scm

--manifest=arquivo

-m arquivo

Create an environment for the packages contained in the manifest object returned by the Scheme code in file. This option can be repeated several times, in which case the manifests are concatenated.

This is similar to the same-named option in guix package (veja --manifest) and uses the same manifest files.

Veja Escrevendo manifestos, for information on how to write a manifest. See --export-manifest below on how to obtain a first manifest.

--export-manifest

Write to standard output a manifest suitable for --manifest corresponding to given command-line options.

This is a way to “convert” command-line arguments into a manifest. For example, imagine you are tired of typing long lines and would like to get a manifest equivalent to this command line:

guix shell -D guile git emacs emacs-geiser emacs-geiser-guile

Just add --export-manifest to the command line above:

guix shell --export-manifest \
  -D guile git emacs emacs-geiser emacs-geiser-guile

... and you get a manifest along these lines:

(concatenate-manifests
  (list (specifications->manifest
          (list "git"
                "emacs"
                "emacs-geiser"
                "emacs-geiser-guile"))
        (package->development-manifest
          (specification->package "guile"))))

You can store it into a file, say manifest.scm, and from there pass it to guix shell or indeed pretty much any guix command:

guix shell -m manifest.scm

Voilà, you’ve converted a long command line into a manifest! That conversion process honors package transformation options (veja Opções de transformação de pacote) so it should be lossless.

--profile=perfil

-p perfil

Create an environment containing the packages installed in profile. Use guix package (veja Invocando guix package) to create and manage profiles.

--pure

Unset existing environment variables when building the new environment, except those specified with --preserve (see below). This has the effect of creating an environment in which search paths only contain package inputs.

--preserve=regexp

-E regexp

When used alongside --pure, preserve the environment variables matching regexp—in other words, put them on a “white list” of environment variables that must be preserved. This option can be repeated several times.

guix shell --pure --preserve=^SLURM openmpi … \
  -- mpirun …

This example runs mpirun in a context where the only environment variables defined are PATH, environment variables whose name starts with ‘SLURM’, as well as the usual “precious” variables (HOME, USER, etc.).

--search-paths

Display the environment variable definitions that make up the environment.

--system=system

-s sistema

Attempt to build for system—e.g., i686-linux.

--container ¶

-C

Run command within an isolated container. The current working directory outside the container is mapped inside the container. Additionally, unless overridden with --user, a dummy home directory is created that matches the current user’s home directory, and /etc/passwd is configured accordingly.

The spawned process runs as the current user outside the container. Inside the container, it has the same UID and GID as the current user, unless --user is passed (see below).

--network

-N

For containers, share the network namespace with the host system. Containers created without this flag only have access to the loopback device.

--link-profile

-P

For containers, link the environment profile to ~/.guix-profile within the container and set GUIX_ENVIRONMENT to that. This is equivalent to making ~/.guix-profile a symlink to the actual profile within the container. Linking will fail and abort the environment if the directory already exists, which will certainly be the case if guix shell was invoked in the user’s home directory.

Certain packages are configured to look in ~/.guix-profile for configuration files and data;¹⁵ --link-profile allows these programs to behave as expected within the environment.

--user=user

-u usuário

For containers, use the username user in place of the current user. The generated /etc/passwd entry within the container will contain the name user, the home directory will be /home/user, and no user GECOS data will be copied. Furthermore, the UID and GID inside the container are 1000. user need not exist on the system.

Additionally, any shared or exposed path (see --share and --expose respectively) whose target is within the current user’s home directory will be remapped relative to /home/USER; this includes the automatic mapping of the current working directory.

# will expose paths as /home/foo/wd, /home/foo/test, and /home/foo/target
cd $HOME/wd
guix shell --container --user=foo \
     --expose=$HOME/test \
     --expose=/tmp/target=$HOME/target

While this will limit the leaking of user identity through home paths and each of the user fields, this is only one useful component of a broader privacy/anonymity solution—not one in and of itself.

--no-cwd

For containers, the default behavior is to share the current working directory with the isolated container and immediately change to that directory within the container. If this is undesirable, --no-cwd will cause the current working directory to not be automatically shared and will change to the user’s home directory within the container instead. See also --user.

--expose=fonte[=alvo]

--share=fonte[=alvo]

For containers, --expose (resp. --share) exposes the file system source from the host system as the read-only (resp. writable) file system target within the container. If target is not specified, source is used as the target mount point in the container.

The example below spawns a Guile REPL in a container in which the user’s home directory is accessible read-only via the /exchange directory:

guix shell --container --expose=$HOME=/exchange guile -- guile

--symlink=spec

-S spec

For containers, create the symbolic links specified by spec, as documented in pack-symlink-option.

--emulate-fhs

-F

When used with --container, emulate a Filesystem Hierarchy Standard (FHS) configuration within the container, providing /bin, /lib, and other directories and files specified by the FHS.

As Guix deviates from the FHS specification, this option sets up the container to more closely mimic that of other GNU/Linux distributions. This is useful for reproducing other development environments, testing, and using programs which expect the FHS specification to be followed. With this option, the container will include a version of glibc that will read /etc/ld.so.cache within the container for the shared library cache (contrary to glibc in regular Guix usage) and set up the expected FHS directories: /bin, /etc, /lib, and /usr from the container’s profile.

--nesting

-W

When used with --container, provide Guix inside the container and arrange so that it can interact with the build daemon that runs outside the container. This is useful if you want, within your isolated container, to create other containers, as in this sample session:

$ guix shell -CW coreutils
[env]$ guix shell -C guile -- guile -c '(display "hello!\n")'
hello!
[env]$ exit

The session above starts a container with coreutils programs available in PATH. From there, we spawn guix shell to create a nested container that provides nothing but Guile.

Another example is evaluating a guix.scm file that is untrusted, as shown here:

guix shell -CW -- guix build -f guix.scm

The guix build command as executed above can only access the current directory.

Under the hood, the -W option does several things:

• mapeie o socket do daemon (por padrão, /var/guix/daemon-socket/socket) dentro do contêiner;
• map the whole store (by default /gnu/store) inside the container such that store items made available by nested guix invocations are visible;
• add the currently-used guix command to the profile in the container, such that guix describe returns the same state inside and outside the container;
• share the cache (by default ~/.cache/guix) with the host, to speed up operations such as guix time-machine and guix shell.

--rebuild-cache ¶

In most cases, guix shell caches the environment so that subsequent uses are instantaneous. Least-recently used cache entries are periodically removed. The cache is also invalidated, when using --file or --manifest, anytime the corresponding file is modified.

The --rebuild-cache forces the cached environment to be refreshed. This is useful when using --file or --manifest and the guix.scm or manifest.scm file has external dependencies, or if its behavior depends, say, on environment variables.

--root=arquivo ¶

-r arquivo

Make file a symlink to the profile for this environment, and register it as a garbage collector root.

This is useful if you want to protect your environment from garbage collection, to make it “persistent”.

When this option is omitted, guix shell caches profiles so that subsequent uses of the same environment are instantaneous—this is comparable to using --root except that guix shell takes care of periodically removing the least-recently used garbage collector roots.

In some cases, guix shell does not cache profiles—e.g., if transformation options such as --with-latest are used. In those cases, the environment is protected from garbage collection only for the duration of the guix shell session. This means that next time you recreate the same environment, you could have to rebuild or re-download packages.

Veja Invocando guix gc, for more on GC roots.

guix shell also supports all of the common build options that guix build supports (veja Opções de compilação comum) as well as package transformation options (veja Opções de transformação de pacote).