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# Preface {#preface}
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2020-04-24 23:36:52 +00:00
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The Nix Packages collection (Nixpkgs) is a set of thousands of packages for the
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[Nix package manager](https://nixos.org/nix/), released under a
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[permissive MIT/X11 license](https://github.com/NixOS/nixpkgs/blob/master/COPYING).
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Packages are available for several platforms, and can be used with the Nix
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package manager on most GNU/Linux distributions as well as [NixOS](https://nixos.org/nixos).
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This manual primarily describes how to write packages for the Nix Packages collection
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(Nixpkgs). Thus it’s mainly for packagers and developers who want to add packages to
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Nixpkgs. If you like to learn more about the Nix package manager and the Nix
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expression language, then you are kindly referred to the [Nix manual](https://nixos.org/nix/manual/).
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The NixOS distribution is documented in the [NixOS manual](https://nixos.org/nixos/manual/).
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2021-06-28 23:13:55 +00:00
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## Overview of Nixpkgs {#overview-of-nixpkgs}
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2020-04-24 23:36:52 +00:00
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Nix expressions describe how to build packages from source and are collected in
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the [nixpkgs repository](https://github.com/NixOS/nixpkgs). Also included in the
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collection are Nix expressions for
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[NixOS modules](https://nixos.org/nixos/manual/index.html#sec-writing-modules).
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With these expressions the Nix package manager can build binary packages.
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Packages, including the Nix packages collection, are distributed through
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[channels](https://nixos.org/nix/manual/#sec-channels). The collection is
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distributed for users of Nix on non-NixOS distributions through the channel
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`nixpkgs`. Users of NixOS generally use one of the `nixos-*` channels, e.g.
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`nixos-19.09`, which includes all packages and modules for the stable NixOS
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19.09. Stable NixOS releases are generally only given
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security updates. More up to date packages and modules are available via the
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`nixos-unstable` channel.
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Both `nixos-unstable` and `nixpkgs` follow the `master` branch of the Nixpkgs
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repository, although both do lag the `master` branch by generally
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[a couple of days](https://status.nixos.org/). Updates to a channel are
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distributed as soon as all tests for that channel pass, e.g.
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[this table](https://hydra.nixos.org/job/nixpkgs/trunk/unstable#tabs-constituents)
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shows the status of tests for the `nixpkgs` channel.
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2020-05-15 21:57:56 +00:00
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The tests are conducted by a cluster called [Hydra](https://nixos.org/hydra/),
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which also builds binary packages from the Nix expressions in Nixpkgs for
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`x86_64-linux`, `i686-linux` and `x86_64-darwin`.
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The binaries are made available via a [binary cache](https://cache.nixos.org).
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The current Nix expressions of the channels are available in the
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[`nixpkgs`](https://github.com/NixOS/nixpkgs) repository in branches
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that correspond to the channel names (e.g. `nixos-19.09-small`).
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