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<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><emphasis>url</emphasis>/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>
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