Name

       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 a set of Nix expressions.

       To see the list of official NixOS channels, visit https://nixos.org/channels.

       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.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"

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”.

                                                                                   nix-channel(1)