Here we assume you’ve already made your first steps with Guix (see 入门) 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,
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 调用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
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 使用配置系统).
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 调用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 介绍). 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 调用guix challenge).
Control over the build environment is a feature that is also useful for
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 调用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.