nix-channel 1 Nix nix-channel manage Nix channels nix-channel --add url name --remove name --list --update names --rollback generation A Nix channel is a mechanism that allows you to automatically stay up-to-date with a set of pre-built Nix expressions. A Nix channel is just a URL that points to a place containing a set of Nix expressions. See also . To see the list of official NixOS channels, visit . This command has the following operations: --add url [name] Adds a channel named name with URL url to the list of subscribed channels. If name is omitted, it defaults to the last component of url, with the suffixes -stable or -unstable removed. --remove name Removes the channel named name from the list of subscribed channels. --list Prints the names and URLs of all subscribed channels on standard output. --update [names…] Downloads the Nix expressions of all subscribed channels (or only those included in names if specified) and makes them the default for nix-env operations (by symlinking them from the directory ~/.nix-defexpr). --rollback [generation] Reverts the previous call to nix-channel --update. Optionally, you can specify a specific channel generation number to restore. Note that --add does not automatically perform an update. The list of subscribed channels is stored in ~/.nix-channels. To subscribe to the Nixpkgs channel and install the GNU Hello package: $ nix-channel --add https://nixos.org/channels/nixpkgs-unstable $ nix-channel --update $ nix-env -iA nixpkgs.hello You can revert channel updates using --rollback: $ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version' "14.04.527.0e935f1" $ nix-channel --rollback switching from generation 483 to 482 $ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version' "14.04.526.dbadfad" /nix/var/nix/profiles/per-user/username/channels nix-channel uses a nix-env profile to keep track of previous versions of the subscribed channels. Every time you run nix-channel --update, a new channel generation (that is, a symlink to the channel Nix expressions in the Nix store) is created. This enables nix-channel --rollback to revert to previous versions. ~/.nix-defexpr/channels This is a symlink to /nix/var/nix/profiles/per-user/username/channels. It ensures that nix-env can find your channels. In a multi-user installation, you may also have ~/.nix-defexpr/channels_root, which links to the channels of the root user. A channel URL should point to a directory containing the following files: nixexprs.tar.xz A tarball containing Nix expressions and files referenced by them (such as build scripts and patches). At the top level, the tarball should contain a single directory. That directory must contain a file default.nix that serves as the channel’s “entry point”.