When using Guix, each package ends up in the package store, in its
own directory—something that resembles
xxx is a base32 string.
Instead of referring to these directories, users have their own
profile, which points to the packages that they actually want to
use. These profiles are stored within each user’s home directory, at
alice installs GCC 4.7.2. As a result,
/home/alice/.guix-profile/bin/gcc points to
/gnu/store/…-gcc-4.7.2/bin/gcc. Now, on the same machine,
bob had already installed GCC 4.8.0. The profile of
simply continues to point to
/gnu/store/…-gcc-4.8.0/bin/gcc—i.e., both versions of GCC
coexist on the same system without any interference.
guix package command is the central tool to manage
packages (see Invoking guix package). It operates on the per-user
profiles, and can be used with normal user privileges.
The command provides the obvious install, remove, and upgrade
operations. Each invocation is actually a transaction: either
the specified operation succeeds, or nothing happens. Thus, if the
guix package process is terminated during the transaction,
or if a power outage occurs during the transaction, then the user’s
profile remains in its previous state, and remains usable.
In addition, any package transaction may be rolled back. So, if, for example, an upgrade installs a new version of a package that turns out to have a serious bug, users may roll back to the previous instance of their profile, which was known to work well. Similarly, the global system configuration on GuixSD is subject to transactional upgrades and roll-back (see Using the Configuration System).
All packages in the package store may be garbage-collected. Guix can determine which packages are still referenced by user profiles, and remove those that are provably no longer referenced (see Invoking guix gc). Users may also explicitly remove old generations of their profile so that the packages they refer to can be collected.
Guix takes a purely functional approach to package management, as described in the introduction (see Introduction). Each /gnu/store package directory name contains a hash of all the inputs that were used to build that package—compiler, libraries, build scripts, etc. This direct correspondence allows users to make sure a given package installation matches the current state of their distribution. It also helps maximize build reproducibility: thanks to the isolated build environments that are used, a given build is likely to yield bit-identical files when performed on different machines (see container).
This foundation allows Guix to support transparent binary/source deployment. When a pre-built binary for a /gnu/store item is available from an external source—a substitute, Guix just downloads it and unpacks it; otherwise, it builds the package from source, locally (see Substitutes). Because build results are usually bit-for-bit reproducible, users do not have to trust servers that provide substitutes: they can force a local build and challenge providers (see Invoking guix challenge).
Control over the build environment is a feature that is also useful for
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 dependencies of the
package into their profile (see Invoking guix environment).
All of Guix and its package definitions is version-controlled, and
guix pull allows you to “travel in time” on the history of Guix
itself (see Invoking guix pull). This makes it possible to replicate a
Guix instance on a different machine or at a later point in time, which in
turn allows you to replicate complete software environments, while
retaining precise provenance tracking of the software.