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# Name
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2020-07-23 10:58:42 +00:00
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2020-07-24 10:56:19 +00:00
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`nix-channel` - manage Nix channels
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2020-07-24 10:56:19 +00:00
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# Synopsis
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2020-07-24 10:56:19 +00:00
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`nix-channel` {`--add` url [*name*] | `--remove` *name* | `--list` | `--update` [*names…*] | `--rollback` [*generation*] }
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# Description
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A Nix channel is a mechanism that allows you to automatically stay
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up-to-date with a set of pre-built Nix expressions. A Nix channel is
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just a URL that points to a place containing a set of Nix expressions.
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To see the list of official NixOS channels, visit
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<https://nixos.org/channels>.
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This command has the following operations:
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- `--add` *url* \[*name*\]\
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Adds a channel named *name* with URL *url* to the list of subscribed
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channels. If *name* is omitted, it defaults to the last component of
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*url*, with the suffixes `-stable` or `-unstable` removed.
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- `--remove` *name*\
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Removes the channel named *name* from the list of subscribed
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channels.
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- `--list`\
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Prints the names and URLs of all subscribed channels on standard
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output.
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- `--update` \[*names*…\]\
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Downloads the Nix expressions of all subscribed channels (or only
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those included in *names* if specified) and makes them the default
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for `nix-env` operations (by symlinking them from the directory
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`~/.nix-defexpr`).
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- `--rollback` \[*generation*\]\
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Reverts the previous call to `nix-channel
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--update`. Optionally, you can specify a specific channel generation
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number to restore.
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Note that `--add` does not automatically perform an update.
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The list of subscribed channels is stored in `~/.nix-channels`.
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# Examples
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To subscribe to the Nixpkgs channel and install the GNU Hello package:
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2020-07-31 13:43:25 +00:00
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```console
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$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
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$ nix-channel --update
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$ nix-env -iA nixpkgs.hello
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```
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You can revert channel updates using `--rollback`:
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```console
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$ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'
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"14.04.527.0e935f1"
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$ nix-channel --rollback
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switching from generation 483 to 482
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$ nix-instantiate --eval -E '(import <nixpkgs> {}).lib.version'
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"14.04.526.dbadfad"
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```
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# Files
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- `/nix/var/nix/profiles/per-user/username/channels`\
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`nix-channel` uses a `nix-env` profile to keep track of previous
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versions of the subscribed channels. Every time you run `nix-channel
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--update`, a new channel generation (that is, a symlink to the
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channel Nix expressions in the Nix store) is created. This enables
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`nix-channel --rollback` to revert to previous versions.
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- `~/.nix-defexpr/channels`\
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This is a symlink to
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`/nix/var/nix/profiles/per-user/username/channels`. It ensures that
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`nix-env` can find your channels. In a multi-user installation, you
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may also have `~/.nix-defexpr/channels_root`, which links to the
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channels of the root user.
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# Channel format
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A channel URL should point to a directory containing the following
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files:
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- `nixexprs.tar.xz`\
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A tarball containing Nix expressions and files referenced by them
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(such as build scripts and patches). At the top level, the tarball
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should contain a single directory. That directory must contain a
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file `default.nix` that serves as the channel’s “entry point”.
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