Definition. A Linux distribution whose entire system configuration is described declaratively in the Nix language. Packages, services, users and configuration files are produced by reproducible builds of the Nix package manager. Every change creates a new “generation” with an atomic switch and rollback. This makes NixOS immutable in the sense of “no drift” while remaining flexible to configure.

Why it matters. NixOS is a pragmatic answer to reproducible server and build environments. It is interesting for mid-sized platforms that want to professionalise build and base image hygiene without going all the way to immutable worker OS setups like Talos or Flatcar. It works for developer machines just as well as for production hosts.

Related. Immutable Infrastructure, Declarative Infrastructure, GitOps, Wolfi OS, Self-hosted Infrastructure