# Channels

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 `nix-env`. Fortunately, there’s a better way: Nix channels.

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 `nix-channel` you can automatically stay up to date with whatever is available at that URL.

You can “subscribe” to a channel using `nix-channel --add`, e.g.,

    $ nix-channel --add https://nixos.org/channels/nixpkgs-unstable

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 `~/.nix-channels`, where it is read by subsequent calls to `nix-channel --update`.) You can “unsubscribe” using `nix-channel --remove`:

    $ nix-channel --remove nixpkgs

To obtain the latest Nix expressions available in a channel, do

    $ nix-channel --update

This downloads and unpacks the Nix expressions in every channel (downloaded from `url/nixexprs.tar.bz2`). It also makes the union of each channel’s Nix expressions available by default to `nix-env` operations (via the symlink `~/.nix-defexpr/channels`). Consequently, you can then say

    $ nix-env -u

to upgrade all packages in your profile to the latest versions available in the subscribed channels.