nix-channel man page

nix-channel — manage Nix channels

Synopsis

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 both a set of Nix expressions and a pointer to a binary cache.

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 <nixpkgs> {}).lib.nixpkgsVersion'
"14.04.527.0e935f1"

$ nix-channel --rollback
switching from generation 483 to 482

$ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.nixpkgsVersion'
"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”.

binary-cache-url

A file containing the URL to a binary cache (such as https://cache.nixos.org). Nix will automatically check this cache for pre-built binaries, if the user has sufficient rights to add binary caches. For instance, in a multi-user Nix setup, the binary caches provided by the channels of the root user are used automatically, but caches corresponding to the channels of non-root users are ignored.

Author

Eelco Dolstra

Author

Info

01/01/1970 Nix 2.2.2 Command Reference