Nix

Nix is a cross-platform package manager and build system that uses a purely functional deployment model. It manages software on Linux, macOS, and other Unix-like systems and serves as the foundation for the NixOS Linux distribution.

The core idea is that software packages and their dependencies are built in isolation and described with the Nix expression language. Packages are stored in a content-addressed store at /nix/store, where each item includes a cryptographic hash of its inputs. This enables multiple versions and configurations to coexist without conflicts, supports reproducible builds, and makes upgrades atomic with straightforward rollbacks.

Nix provides tools such as nix-env for user environments and nix-build to build derivations, along with nix-store for store management and the Nix daemon for multi-user operation. NixOS integrates the package manager with a declarative system configuration, where the entire system state is described in configuration files and can be rebuilt deterministically.

The Nix project was initiated by Eelco Dolstra in the early 2000s. NixOS emerged as a distribution built on top of the Nix package manager, emphasizing reproducibility and isolation. The Nix language is a lazy, purely functional language used to describe package derivations and system configurations.

Beyond its original scope, Nix is used for reproducible environments, continuous integration workflows, and configuration management in various forms, with ongoing development and additions such as the Flakes feature to improve composability and reproducibility.