Guix

Guix Profiles in Practice

Pierre Neidhardt — 25 жовтня 2019 року

Note: An updated version of this article is available in the brand new cookbook.

Guix provides a very useful feature that may be quite foreign to newcomers: profiles. They are a way to group package installations together and all users on the same system are free to use as many profiles as they want.

Whether you're a developer or not, you may find that multiple profiles bring you great power and flexibility. While they shift the paradigm somewhat compared to traditional package managers, they are very convenient to use once you've understood how to set them up.

If you are familiar with Python's virtualenv, you can think of a profile as a kind of universal virtualenv that can hold any kind of software whatsoever, not just Python software. Furthermore, profiles are self-sufficient: they capture all the runtime dependencies which guarantees that all programs within a profile will always work at any point in time.

Multiple profiles have many benefits:

Concretely, here follows some typical profiles:

Let's dive in the set up!

Basic setup with manifests

A Guix profile can be set up via a so-called manifest specification that looks like this:

(specifications->manifest
  '("package-1"
    ;; Version 1.3 of package-2.
    "package-2@1.3"
    ;; The "lib" output of package-3.
    "package-3:lib"
    ; ...
    "package-N"))

See (guix) Invoking guix package for the syntax details.

We can create a manifest specification per profile and install them this way:

GUIX_EXTRA_PROFILES=$HOME/.guix-extra-profiles
mkdir -p "$GUIX_EXTRA_PROFILES"/my-project # if it does not exist yet
guix package --manifest=/path/to/guix-my-project-manifest.scm --profile="$GUIX_EXTRA_PROFILES"/my-project/my-project

Here we set an arbitrary variable GUIX_EXTRA_PROFILES to point to the directory where we will store our profiles in the rest of this article.

Placing all your profiles in a single directory, with each profile getting its own sub-directory, is somewhat cleaner. This way, each sub-directory will contain all the symlinks for precisely one profile. Besides, "looping over profiles" becomes obvious from any programming language (e.g. a shell script) by simply looping over the sub-directories of $GUIX_EXTRA_PROFILES.

Note that it's also possible to loop over the output of

guix package --list-profiles

although you'll probably have to filter out ~/.config/guix/current.

To enable all profiles on login, add this to your ~/.bash_profile (or similar):

for i in $GUIX_EXTRA_PROFILES/*; do
    profile=$i/$(basename "$i")
    if [ -f "$profile"/etc/profile ]; then
        GUIX_PROFILE="$profile"
        . "$GUIX_PROFILE"/etc/profile
    fi
    unset profile
done

Note to Guix System users: the above reflects how your default profile ~/.guix-profile is activated from /etc/profile, that latter being loaded by ~/.bashrc by default.

You can obviously choose to only enable a subset of them:

for i in "$GUIX_EXTRA_PROFILES"/my-project-1 "$GUIX_EXTRA_PROFILES"/my-project-2; do
    profile=$i/$(basename "$i")
    if [ -f "$profile"/etc/profile ]; then
        GUIX_PROFILE="$profile"
        . "$GUIX_PROFILE"/etc/profile
    fi
    unset profile
done

When a profile is off, it's straightforward to enable it for an individual shell without "polluting" the rest of the user session:

GUIX_PROFILE="path/to/my-project" ; . "$GUIX_PROFILE"/etc/profile

The key to enabling a profile is to source its etc/profile file. This file contains shell code that exports the right environment variables necessary to activate the software contained in the profile. It is built automatically by Guix and meant to be sourced. It contains the same variables you would get if you ran:

guix package --search-paths=prefix --profile=$my_profile"

Once again, see (guix) Invoking guix package for the command line options.

To upgrade a profile, simply install the manifest again:

guix package -m /path/to/guix-my-project-manifest.scm -p "$GUIX_EXTRA_PROFILES"/my-project/my-project

To upgrade all profiles, it's easy enough to loop over them. For instance, assuming your manifest specifications are stored in ~/.guix-manifests/guix-$profile-manifest.scm, with $profile being the name of the profile (e.g. "project1"), you could do the following in Bourne shell:

for profile in "$GUIX_EXTRA_PROFILES"/*; do
  guix package --profile="$profile" --manifest="$HOME/.guix-manifests/guix-$profile-manifest.scm"
done

Each profile has its own generations:

guix package -p "$GUIX_EXTRA_PROFILES"/my-project/my-project --list-generations

You can roll-back to any generation of a given profile:

guix package -p "$GUIX_EXTRA_PROFILES"/my-project/my-project --switch-generations=17

Required packages

Activating a profile essentially boils down to exporting a bunch of environmental variables. This is the role of the etc/profile within the profile.

Note: Only the environmental variables of the packages that consume them will be set.

For instance, MANPATH won't be set if there is no consumer application for man pages within the profile. So if you need to transparently access man pages once the profile is loaded, you've got two options:

The same is true for INFOPATH (you can install info-reader), PKG_CONFIG_PATH (install pkg-config), etc.

Default profile

What about the default profile that Guix keeps in ~/.guix-profile?

You can assign it the role you want. Typically you would install the manifest of the packages you want to use all the time.

Alternatively, you could keep it "manifest-less" for throw-away packages that you would just use for a couple of days. This way makes it convenient to run

guix install package-foo
guix upgrade package-bar

without having to specify the path to a profile.

The benefits of manifests

Manifests are a convenient way to keep your package lists around and, say, to synchronize them across multiple machines using a version control system.

A common complaint about manifests is that they can be slow to install when they contain large number of packages. This is especially cumbersome when you just want get an upgrade for one package within a big manifest.

This is one more reason to use multiple profiles, which happen to be just perfect to break down manifests into multiple sets of semantically connected packages. Using multiple, small profiles provides more flexibility and usability.

Manifests come with multiple benefits. In particular, they ease maintenance:

It's important to understand that while manifests can be used to declare profiles, they are not strictly equivalent: profiles have the side effect that they "pin" packages in the store, which prevents them from being garbage-collected and ensures that they will still be available at any point in the future.

Let's take an example:

  1. We have an environment for hacking on a project for which there isn't a Guix package yet. We build the environment using a manifest, and then run guix environment -m manifest.scm. So far so good.

  2. Many weeks pass and we have run a couple of guix pull in the mean time. Maybe a dependency from our manifest has been updated; or we may have run guix gc and some packages needed by our manifest have been garbage-collected.

  3. Eventually, we set to work on that project again, so we run guix environment -m manifest.scm. But now we have to wait for Guix to build and install stuff!

Ideally, we could spare the rebuild time. And indeed we can, all we need is to install the manifest to a profile and use GUIX_PROFILE=/the/profile; . "$GUIX_PROFILE"/etc/profile as explained above: this guarantees that our hacking environment will be available at all times.

Security warning: While keeping old profiles around can be convenient, keep in mind that outdated packages may not have received the latest security fixes.

Reproducible profiles

To reproduce a profile bit-for-bit, we need two pieces of information:

Indeed, manifests alone might not be enough: different Guix versions (or different channels) can produce different outputs for a given manifest.

You can output the Guix channel specification with guix describe --format=channels. Save this to a file, say channel-specs.scm.

On another computer, you can use the channel specification file and the manifest to reproduce the exact same profile:

GUIX_EXTRA_PROFILES=$HOME/.guix-extra-profiles
GUIX_EXTRA=$HOME/.guix-extra

mkdir "$GUIX_EXTRA"/my-project
guix pull --channels=channel-specs.scm --profile "$GUIX_EXTRA/my-project/guix"

mkdir -p "$GUIX_EXTRA_PROFILES/my-project"
"$GUIX_EXTRA"/my-project/guix/bin/guix package --manifest=/path/to/guix-my-project-manifest.scm --profile="$GUIX_EXTRA_PROFILES"/my-project/my-project

It's safe to delete the Guix channel profile you've just installed with the channel specification, the project profile does not depend on it.

Special thanks

Chris Marusich and Simon Tournier for their thorough feedback.

About GNU Guix

GNU Guix is a transactional package manager and an advanced distribution of the GNU system that respects user freedom. Guix can be used on top of any system running the kernel Linux, or it can be used as a standalone operating system distribution for i686, x86_64, ARMv7, and AArch64 machines.

In addition to standard package management features, Guix supports transactional upgrades and roll-backs, unprivileged package management, per-user profiles, and garbage collection. When used as a standalone GNU/Linux distribution, Guix offers a declarative, stateless approach to operating system configuration management. Guix is highly customizable and hackable through Guile programming interfaces and extensions to the Scheme language.

Пов'язані теми:

Cookbook Customization Functional package management Reproducibility Software development User interfaces

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