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Here we assume you’ve already made your first steps with Guix (see Getting Started) and would like to get an overview about what’s going on under the hood.
When using Guix, each package ends up in the package store, in its
own directory—something that resembles
/gnu/store/xxx-package-1.2, where 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
$HOME/.guix-profile
.
For example, 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 bob
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.
The 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 Guix is subject to transactional upgrades and roll-back (see Getting Started).
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
developers. The guix shell
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 shell
).
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.
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