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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
<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”.
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