nix/doc/manual/source/command-ref/nix-channel.md

Name

nix-channel - manage Nix channels

Synopsis

nix-channel {--add url [name] | --remove name | --list | --update [names…] | --list-generations | --rollback [generation] }

Description

Channels are a mechanism for referencing remote Nix expressions and conveniently retrieving their latest version.

The moving parts of channels are:

• The official channels listed at https://nixos.org/channels
• The user-specific list of subscribed channels
• The downloaded channel contents
• The Nix expression search path, set with the -I option or the NIX_PATH environment variable

Note

The state of a subscribed channel is external to the Nix expressions relying on it. This may limit reproducibility.

Dependencies on other Nix expressions can be declared explicitly with:

• fetchurl, fetchTarball, or fetchGit in Nix expressions
• the -I option in command line invocations

This command has the following operations:

• --add url [name]

  Add a channel name located at url to the list of subscribed channels. If name is omitted, default to the last component of url, with the suffixes -stable or -unstable removed.

  Note

  --add does not automatically perform an update. Use --update explicitly.

  A channel URL must point to a directory containing a file nixexprs.tar.gz. At the top level, that tarball must contain a single directory with a default.nix file that serves as the channel’s entry point.

• --remove name

  Remove the channel name from the list of subscribed channels.

• --list

  Print the names and URLs of all subscribed channels on standard output.

• --update [names…]

  Download the Nix expressions of subscribed channels and create a new generation. Update all channels if none is specified, and only those included in names otherwise.

  Note

  --update uses fetchTarball under the hood, so it will cache channels. Use --tarball-ttl or the nix configuration option tarball-ttl to change this behavior.

• --list-generations

  Prints a list of all the current existing generations for the channel profile.

  Works the same way as

  nix-env --profile /nix/var/nix/profiles/per-user/$USER/channels --list-generations
  

• --rollback [generation]

  Revert channels to the state before the last call to nix-channel --update. Optionally, you can specify a specific channel generation number to restore.

{{#include ./opt-common.md}}

{{#include ./env-common.md}}

Files

nix-channel operates on the following files.

{{#include ./files/channels.md}}

Examples

Subscribe to the Nixpkgs channel and run hello from the GNU Hello package:

$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
$ nix-channel --list
nixpkgs https://nixos.org/channels/nixpkgs
$ nix-channel --update
$ nix-shell -p hello --run hello
hello

Revert channel updates using --rollback:

$ nix-instantiate --eval '<nixpkgs>' --attr lib.version
"22.11pre296212.530a53dcbc9"

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

$ nix-instantiate --eval '<nixpkgs>' --attr lib.version
"22.11pre281526.d0419badfad"

Remove a channel:

$ nix-channel --remove nixpkgs
$ nix-channel --list