gitlab-org--gitlab-foss/doc/administration/server_hooks.md

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reference, howto	https://docs.gitlab.com/ee/administration/custom_hooks.html

Server hooks (CORE ONLY)

Notes:

• Server hooks were introduced in GitLab 12.8 replacing Custom Hooks.
• Server hooks must be configured on the filesystem of the GitLab server. Only GitLab server administrators will be able to complete these tasks. Please explore webhooks and GitLab CI/CD as an option if you do not have filesystem access. For a user-configurable Git hook interface, see Push Rules, available in GitLab Starter (STARTER).
• Server hooks won't be replicated to secondary nodes if you use GitLab Geo.

Git natively supports hooks that are executed on different actions. Examples of server-side Git hooks include pre-receive, post-receive, and update. See Git SCM Server-Side Hooks for more information about each hook type.

As of GitLab Shell version 2.2.0 (which requires GitLab 7.5+), GitLab administrators can add custom Git hooks to any GitLab project.

Create a server hook for a repository

Server-side Git hooks are typically placed in the repository's hooks subdirectory. In GitLab, hook directories are symlinked to the GitLab Shell hooks directory for ease of maintenance between GitLab Shell upgrades. Server hooks are implemented differently, but the behavior is exactly the same once the hook is created. Follow the steps below to set up a server hook for a repository:

1. Pick a project that needs a server hook.
2. On the GitLab server, navigate to the project's repository directory. For an installation from source the path is usually /home/git/repositories/<group>/<project>.git. For Omnibus installs the path is usually /var/opt/gitlab/git-data/repositories/<group>/<project>.git.
3. Create a new directory in this location called custom_hooks.
4. Inside the new custom_hooks directory, create a file with a name matching the hook type. For a pre-receive hook the file name should be pre-receive with no extension.
5. Make the hook file executable and make sure it's owned by Git.
6. Write the code to make the server hook function as expected. Hooks can be in any language. Ensure the 'shebang' at the top properly reflects the language type. For example, if the script is in Ruby the shebang will probably be #!/usr/bin/env ruby.

That's it! Assuming the hook code is properly implemented the hook will fire as appropriate.

Set a global server hook for all repositories

To create a Git hook that applies to all of your repositories in your instance, set a global server hook. Since GitLab will look inside the GitLab Shell hooks directory for global hooks, adding any hook there will apply it to all repositories. Follow the steps below to properly set up a server hook for all repositories:

1. On the GitLab server, navigate to the configured custom hook directory. The default is in the GitLab Shell directory. The GitLab Shell hook directory for an installation from source the path is usually /home/git/gitlab-shell/hooks. For Omnibus installs the path is usually /opt/gitlab/embedded/service/gitlab-shell/hooks. To look in a different directory for the global custom hooks, set custom_hooks_dir in the GitLab Shell config. For Omnibus installations, this can be set in gitlab.rb; and in source installations, this can be set in gitlab-shell/config.yml.
2. Create a new directory in this location. Depending on your hook, it will be either a pre-receive.d, post-receive.d, or update.d directory.
3. Inside this new directory, add your hook. Hooks can be in any language. Ensure the 'shebang' at the top properly reflects the language type. For example, if the script is in Ruby the shebang will probably be #!/usr/bin/env ruby.
4. Make the hook file executable and make sure it's owned by Git.

Now test the hook to check whether it is functioning properly.

Chained hooks support

Introduced in GitLab Shell 4.1.0 and GitLab 8.15.

Hooks can be also global or be set per project directories and support a chained execution of the hooks.

NOTE: Note: <hook_name>.d would need to be either pre-receive.d, post-receive.d, or update.d to work properly. Any other names will be ignored.

NOTE: Note: Files in .d directories need to be executable and not match the backup file pattern (*~).

The hooks are searched and executed in this order:

1. Built-in GitLab server hooks (not user-customizable).
2. <project>.git/custom_hooks/<hook_name> - per-project hook (this was kept as the already existing behavior).
3. <project>.git/custom_hooks/<hook_name>.d/* - per-project hooks.
4. <custom_hooks_dir>/<hook_name>.d/* - global hooks: all executable files (except editor backup files).

The hooks of the same type are executed in order and execution stops on the first script exiting with a non-zero value.

For <project>.git you'll need to translate your project name into the hashed storage format that GitLab uses.

Custom error messages

Introduced in GitLab 8.10.

To have custom error messages appear in GitLab's UI when the commit is declined or an error occurs during the Git hook, your script should:

• 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.

Example custom error message

This hook script written in bash will generate the following message in GitLab's UI:

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