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# Name
`nix-channel` - manage Nix channels
# Synopsis
`nix-channel` {`--add` url [*name*] | `--remove` *name* | `--list` | `--update` [*names…*] | `--list-generations` | `--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.
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*\
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`).
- `--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` \[*generation*\]\
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`.
{{#include ./opt-common.md}}
{{#include ./env-common.md}}
# Files
`nix-channel` operates on the following files.
{{#include ./files/channels.md}}
# Examples
To subscribe to the Nixpkgs channel and install the GNU Hello package:
```console
$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
$ nix-channel --update
$ nix-env --install --attr nixpkgs.hello
```
You can revert channel updates using `--rollback`:
```console
$ nix-instantiate --eval --expr '(import <nixpkgs> {}).lib.version'
"14.04.527.0e935f1"
$ nix-channel --rollback
switching from generation 483 to 482
$ nix-instantiate --eval --expr '(import <nixpkgs> {}).lib.version'
"14.04.526.dbadfad"
```
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