Nix package manager

Nix is a package manager for computer systems. Like RPM, APT and many other package managers, it is able to control the installation of packages, or named and versioned groups of files, such as software applications or their associated configuration data.

Nix packages are configured using a lazy, purely functional language especially designed for this purpose; shell scripts or any other external program (such as Make) may be used to build packages from source code. The purely functional nature of the system enables very precise dependency tracking; for example, a binary package has a dependency on the corresponding source package, on the compiler, and on other packages that the build requires. Cryptographic hashes determine the exact build and run-time dependencies of every package, and each source or binary package is represented by such a hash. As a result, binary package repositories are a transparent optimization of the basic operation of the package manager (similar to a "cache" of packages indexed by a cryptographic hash).

Dependencies are resolved by a system functionally equivalent to hard linking, in that versions of software being depended on by a package are not removed until no package is dependent on them. This can lead to greater storage needs, but makes all upgrades safe (guaranteed not to break existing applications) and atomic. It also permits multiple versions of any package, including parametrised packages such as a program with and without a certain feature, to coexist with no interference.

Nix depends upon having its own directory structure for installing the packages. All packages are installed in sub-directories of the nix directory. In naming the folders, different versions of a package are identified by prepending the hash to the package name.

Nix can be used, with some caveats, as a package manager on top of an existing operating system, such as a GNU/Linux distribution. It may also be used to maintain any kind of file configurations, such as server setups, in addition to software packages in the strict sense.