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What I missed when I began using Nix and NixOS was a clear overview of how packages, channels, Hydra, the master branch and updates to channels relate to each other. I've noticed I am not the only one, given the amount of times these questions pop up. For now I propose to include this in the Nixpkgs manual, since this seems to be the best fit. However, I think it would be good to include this in either a new manual, i.e., a user manual, or an 'official' tutorial.
49 lines
2.8 KiB
Markdown
49 lines
2.8 KiB
Markdown
---
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title: Introduction
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author: Frederik Rietdijk
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date: 2015-11-25
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---
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# Introduction
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The Nix Packages collection (Nixpkgs) is a set of over 30,000 packages for the
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[Nix package manager](http://nixos.org/nix/), released under a [permissive MIT/X11 license](https://github.com/NixOS/nixpkgs/blob/master/COPYING).
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Packages are available for several architectures, and can be used with the Nix package manager
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on most GNU/Linux distributions as well as NixOS.
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This manual describes how to write packages for the Nix Packages collection
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(Nixpkgs). Thus it’s 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](http://nixos.org/nix/manual/).
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## Overview of Nixpkgs
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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 [NixOS modules](http://nixos.org/nixos/manual/index.html#sec-writing-modules). With
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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](http://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-15.09`, which includes all packages and modules for the stable NixOS
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15.09. The channels of the 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 [a couple of days](http://howoldis.herokuapp.com/). Updates to a channel are distributed as
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soon as all tests for that channel pass, e.g. [this table](http://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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The tests are conducted by a cluster called [Hydra](http://nixos.org/hydra/),
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which also builds binary packages from the Nix expressions in Nixpkgs. As soon
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as a channel is updated, the binaries are made available via a [binary cache](https://cache.nixos.org). Until the channel updates, binaries that have
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already been built, are available via [Hydra's binary cache](https://hydra.nixos.org).
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The current Nix expressions of the channels are available in the
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[`nixpkgs-channels`](https://github.com/NixOS/nixpkgs-channels) repository,
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which has branches corresponding to the available channels. There is also the
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Nixpkgs Monitor which keeps track of updates and security vulnerabilities.
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