nix-channel 1 Nix nix-channel manage Nix channels nix-channel \--add url name \--remove name \--list \--update names \--rollback generation # Description 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 [???](#sec-channels). 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`. # Examples 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 {}).lib.version' "14.04.527.0e935f1" $ nix-channel --rollback switching from generation 483 to 482 $ nix-instantiate --eval -E '(import {}).lib.version' "14.04.526.dbadfad" # Files - `/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. # Channel format 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”.