GNU Guix1 is a functional package management tool for the GNU system. Package management consists of all activities that relate to building packages from sources, honoring their build-time and run-time dependencies, installing packages in user environments, upgrading installed packages to new versions or rolling back to a previous set, removing unused software packages, etc.
The term functional refers to a specific package management discipline. In Guix, the package build and installation process is seen as a function, in the mathematical sense. That function takes inputs, such as build scripts, a compiler, and libraries, and returns an installed package. As a pure function, its result depends solely on its inputs—for instance, it cannot refer to software or scripts that were not explicitly passed as inputs. A build function always produces the same result when passed a given set of inputs. It cannot alter the system’s environment in any way; for instance, it cannot create, modify, or delete files outside of its build and installation directories. This is achieved by running build processes in isolated environments (or containers), where only their explicit inputs are visible.
The result of package build functions is cached in the file system, in a special directory called the store (see The Store). Each package is installed in a directory of its own, in the store—by default under /gnu/store. The directory name contains a hash of all the inputs used to build that package; thus, changing an input yields a different directory name.
This approach is the foundation of Guix’s salient features: support for transactional package upgrade and rollback, per-user installation, and garbage collection of packages (see Features).
Guix has a command-line interface, which allows users to build, install, upgrade, and remove packages, as well as a Scheme programming interface.
Last but not least, Guix is used to build a distribution of the GNU system, with many GNU and non-GNU free software packages. The Guix System Distribution, or GNU GuixSD, takes advantage of the core properties of Guix at the system level. With GuixSD, users declare all aspects of the operating system configuration, and Guix takes care of instantiating that configuration in a reproducible, stateless fashion. See GNU Distribution.
“Guix” is pronounced like “geeks”, or “ɡiːks” using the international phonetic alphabet (IPA).