Git server hooks

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Renamed from server hooks to Git server hooks in GitLab 15.6.

Git server hooks (not to be confused with system hooks or file hooks) run custom logic on the GitLab server. You can use them to run Git-related tasks such as:

Enforcing specific commit policies.
Performing tasks based on the state of the repository.

Git server hooks use pre-receive, post-receive, and update Git server-side hooks.

GitLab administrators configure server hooks using the gitaly command, which also:

Is used to launch a Gitaly server.
Provides several subcommands.
Connects to the Gitaly gRPC API.

If you don't have access to the gitaly command, alternatives to server hooks include:

Webhooks.
GitLab CI/CD.
Push rules, for a user-configurable Git hook interface.

Geo doesn't replicate server hooks to secondary nodes.

Set server hooks for a repository

::Tabs

:::TabTitle GitLab 15.11 and later

Introduced in GitLab 15.11, hooks set command replaces direct file system access. Existing Git hooks don't need migrating for the hooks set command.

Prerequisites:

The storage name, path to the Gitaly configuration file (default is /var/opt/gitlab/gitaly/config.toml on Linux package instances), and the repository relative path for the repository.
Any language runtimes and utilities that are required by the hooks must be installed on each of the servers that run Gitaly.

To set server hooks for a repository:

Create tarball containing custom hooks:
1. Write the code to make the server hook function as expected. Git server hooks can be in any programming language. Ensure the shebang at the top reflects the language type. For example, if the script is in Ruby the shebang is probably #!/usr/bin/env ruby.
  - To create a single server hook, create a file with a name that matches the hook type. For example, for a pre-receive server hook, the filename should be pre-receive with no extension.
  - To create many server hooks, create a directory for the hooks that matches the hook type. For example, for a pre-receive server hook, the directory name should be pre-receive.d. Put the files for the hook in that directory.
2. Ensure the server hook files are executable and do not match the backup file pattern (*~). The server hooks be in a custom_hooks directory that is at the root of the tarball.
3. Create the custom hooks archive with the tar command. For example, tar -cf custom_hooks.tar custom_hooks.
Run the hooks set subcommand with required options to set the Git hooks for the repository. For example, cat custom_hooks.tar | sudo /opt/gitlab/embedded/bin/gitaly hooks set --storage <storage> --repository <relative path> --config <config path>.
- A path to a valid Gitaly configuration for the node is required to connect to the node and provided to the --config flag.
- Custom hooks tarball must be passed via stdin. For example, cat custom_hooks.tar | sudo /opt/gitlab/embedded/bin/gitaly hooks set --storage <storage> --repository <relative path> --config <config path>.
If you are using Gitaly Cluster, you must run hooks set subcommand on all Gitaly nodes. For more information, see Server hooks on a Gitaly Cluster.

If you implemented the server hook code correctly, it should execute when the Git hook is next triggered.

:::TabTitle GitLab 15.10 and earlier

To create server hooks for a repository:

On the left sidebar, at the bottom, select Admin Area.
Go to Overview > Projects and select the project you want to add a server hook to.
On the page that appears, locate the value of Relative path. This path is where server hooks must be located.
- If you are using hashed storage, see Translate hashed storage paths for information on interpreting the relative path.
- If you are not using hashed storage:
  - For Linux package installations, the path is usually /var/opt/gitlab/git-data/repositories/<group>/<project>.git.
  - For self-compiled installations, the path is usually /home/git/repositories/<group>/<project>.git.
On the file system, create a new directory in the correct location called custom_hooks.
In the new custom_hooks directory:
- To create a single server hook, create a file with a name that matches the hook type. For example, for a pre-receive server hook, the filename should be pre-receive with no extension.
- To create many server hooks, create a directory for the hooks that matches the hook type. For example, for a pre-receive server hook, the directory name should be pre-receive.d. Put the files for the hook in that directory.
Make the server hook files executable and ensure that they are owned by the Git user.
Write the code to make the server hook function as expected. Git server hooks can be in any programming language. Ensure the shebang at the top reflects the language type. For example, if the script is in Ruby the shebang is probably #!/usr/bin/env ruby.
Ensure the hook file does not match the backup file pattern (*~).
If you are using Gitaly Cluster, you must repeat this process on all Gitaly nodes. For more information, see Server hooks on a Gitaly Cluster.

If the server hook code is properly implemented, it should execute when the Git hook is next triggered.

::EndTabs

Server hooks on a Gitaly Cluster

If you use Gitaly Cluster, an individual repository may be replicated to multiple Gitaly storages in Praefect. Consequentially, the hook scripts must be copied to every Gitaly node that has a replica of the repository. To accomplish this, follow the same steps for setting custom repository hooks for the applicable version and repeat for each storage.

The location to copy the scripts to depends on where repositories are stored:

In GitLab 15.2 and earlier, Gitaly Cluster uses the hashed storage path reported by the GitLab application.
In GitLab 15.3 and later, new repositories are created using Praefect-generated replica paths, which are not the hashed storage path. The replica path can be identified by querying the Praefect repository metadata using -relative-path to specify the expected GitLab hashed storage path.

Create global server hooks for all repositories

To create a Git hook that applies to all repositories, set a global server hook. Global server hooks also apply to:

Project and group wiki repositories. Their storage directory names are in the format <id>.wiki.git.
Design management repositories under a project. Their storage directory names are in the format <id>.design.git.

Choose a server hook directory

Before creating a global server hook, you must choose a directory for it.

For Linux package installations, the directory is set in gitlab.rb under gitaly['configuration'][:hooks][:custom_hooks_dir]. You can either:

Use the default suggestion of the /var/opt/gitlab/gitaly/custom_hooks directory by uncommenting it.
Add your own setting.

For self-compiled installations:

The directory is set in gitaly/config.toml under the [hooks] section. However, GitLab honors the custom_hooks_dir value in gitlab-shell/config.yml if the value in gitaly/config.toml is blank or non-existent.
The default directory is /home/git/gitlab-shell/hooks.

Create the global server hook

To create a global server hook for all repositories:

On the GitLab server, go to the configured global server hook directory.
In the configured global server hook directory, create a directory for the hooks that matches the hook type. For example, for a pre-receive server hook, the directory name should be pre-receive.d.
Inside this new directory, add your server hooks. Git server hooks can be in any programming language. Ensure the shebang at the top reflects the language type. For example, if the script is in Ruby the shebang is probably #!/usr/bin/env ruby.
Make the hook file executable, ensure that it's owned by the Git user, and ensure it does not match the backup file pattern (*~).

If the server hook code is properly implemented, it should execute when the Git hook is next triggered. Hooks are executed in alphabetical order by filename in the hook type subdirectories.

Remove server hooks for a repository

::Tabs

:::TabTitle GitLab 15.11 and later

Introduced in GitLab 15.11, hooks set command replaces direct file system access.

Prerequisites:

The storage name and relative path for the repository.

To remove server hooks, pass an empty tarball to hook set to indicate that the repository should contain no hooks. For example:

cat empty_hooks.tar | sudo /opt/gitlab/embedded/bin/gitaly hooks set --storage <storage> --repository <relative path> --config <config path>

:::TabTitle GitLab 15.10 and earlier

To remove server hooks:

Go to the location of the repository on disk.
Delete the server hooks in the custom_hooks directory.

::EndTabs

Chained server hooks

GitLab can execute server hooks in a chain. GitLab searches for and executes server hooks in the following order:

Built-in GitLab server hooks. These server hooks are not customizable by users.
<project>.git/custom_hooks/<hook_name>: Per-project hooks. This location is kept for backwards compatibility.
<project>.git/custom_hooks/<hook_name>.d/*: Location for per-project hooks.
<custom_hooks_dir>/<hook_name>.d/*: Location for all executable global hook files except editor backup files.

Within a server hooks directory, hooks:

Are executed in alphabetical order.
Stop executing when a hook exits with a non-zero value.

Environment variables available to server hooks

You can pass any environment variable to server hooks, but you should only rely on supported environment variables.

The following GitLab environment variables are supported for all server hooks:

Environment variable	Description
`GL_ID`	GitLab identifier of user or SSH key that initiated the push. For example, `user-2234` or `key-4`.
`GL_PROJECT_PATH`	GitLab project path.
`GL_PROTOCOL`	Protocol used for this change. One of: `http` (Git `push` using HTTP), `ssh` (Git `push` using SSH), or `web` (all other actions).
`GL_REPOSITORY`	`project-<id>` where `id` is the ID of the project.
`GL_USERNAME`	GitLab username of the user that initiated the push.

The following Git environment variables are supported for pre-receive and post-receive server hooks:

Environment variable	Description
`GIT_ALTERNATE_OBJECT_DIRECTORIES`	Alternate object directories in the quarantine environment. See Git `receive-pack` documentation.
`GIT_OBJECT_DIRECTORY`	GitLab project path in the quarantine environment. See Git `receive-pack` documentation.
`GIT_PUSH_OPTION_COUNT`	Number of push options. See Git `pre-receive` documentation.
`GIT_PUSH_OPTION_<i>`	Value of push options where `i` is from `0` to `GIT_PUSH_OPTION_COUNT - 1`. See Git `pre-receive` documentation.

Custom error messages

You can have custom error messages appear in the GitLab UI when a commit is declined or an error occurs during the Git hook. To display a custom error message, your script must:

Send the custom error messages to either the script's stdout or stderr.
Prefix each message with GL-HOOK-ERR: with no characters appearing before the prefix.

For example:

#!/bin/sh
echo "GL-HOOK-ERR: My custom error message.";
exit 1