<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude" version="5.0" xml:id="sec-channels"> <title>Channels</title> <para>If you want to stay up to date with a set of packages, it’s not very convenient to manually download the latest set of Nix expressions for those packages and upgrade using <command>nix-env</command>. Fortunately, there’s a better way: <emphasis>Nix channels</emphasis>.</para> <para>A Nix channel is just a URL that points to a place that contains a set of Nix expressions and a manifest. Using the command <link linkend="sec-nix-channel"><command>nix-channel</command></link> you can automatically stay up to date with whatever is available at that URL.</para> <para>To see the list of official NixOS channels, visit <link xlink:href="https://nixos.org/channels" />.</para> <para>You can “subscribe” to a channel using <command>nix-channel --add</command>, e.g., <screen> $ nix-channel --add https://nixos.org/channels/nixpkgs-unstable</screen> subscribes you to a channel that always contains that latest version of the Nix Packages collection. (Subscribing really just means that the URL is added to the file <filename>~/.nix-channels</filename>, where it is read by subsequent calls to <command>nix-channel --update</command>.) You can “unsubscribe” using <command>nix-channel --remove</command>: <screen> $ nix-channel --remove nixpkgs </screen> </para> <para>To obtain the latest Nix expressions available in a channel, do <screen> $ nix-channel --update</screen> This downloads and unpacks the Nix expressions in every channel (downloaded from <literal><replaceable>url</replaceable>/nixexprs.tar.bz2</literal>). It also makes the union of each channel’s Nix expressions available by default to <command>nix-env</command> operations (via the symlink <filename>~/.nix-defexpr/channels</filename>). Consequently, you can then say <screen> $ nix-env -u</screen> to upgrade all packages in your profile to the latest versions available in the subscribed channels.</para> </chapter>