Add document on restarting GitLab

[ci skip]

doc/README.md

@@ -53,6 +53,7 @@
 
 - [Custom git hooks](hooks/custom_hooks.md) Custom git hooks (on the filesystem) for when web hooks aren't enough.
 - [Install](install/README.md) Requirements, directory structures and installation from source.
+- [Restart GitLab](administration/restart_gitlab.md) Learn how to restart GitLab and its components
 - [Integration](integration/README.md) How to integrate with systems such as JIRA, Redmine, LDAP and Twitter.
 - [Issue closing](customization/issue_closing.md) Customize how to close an issue from commit messages.
 - [Libravatar](customization/libravatar.md) Use Libravatar for user avatars.

doc/administration/restart_gitlab.md

+# How to restart GitLab
+
+Depending on how you installed GitLab, there are different methods to restart
+its service(s).
+
+If you want the TL;DR versions, jump to:
+
+- [Omnibus GitLab restart](#omnibus-gitlab-restart)
+- [Omnibus GitLab reconfigure](#omnibus-gitlab-reconfigure)
+- [Source installation restart](#installations-from-source)
+
+## Omnibus installations
+
+If you have used the [Omnibus packages][omnibus-dl] to install GitLab, then
+you should already have `gitlab-ctl` in your `PATH`. To find out, run:
+
+```bash
+which gitlab-ctl
+```
+
+The output should be: `/usr/bin/gitlab-ctl`.
+
+`gitlab-ctl` interacts with the Omnibus packages and can be used to restart the
+GitLab Rails application (Unicorn) as well as the other components, like:
+
+- GitLab Workhorse
+- Sidekiq
+- PostgreSQL (if you are using the bundled one)
+- NGINX (if you are using the bundled one)
+- Redis (if you are using the bundled one)
+- [Mailroom][]
+- Logrotate.
+
+### Omnibus GitLab restart
+
+When you are asked to _restart GitLab_, you need to run the following command:
+
+```bash
+sudo gitlab-ctl restart
+```
+
+The output should be similar to this:
+
+```
+ok: run: gitlab-workhorse: (pid 11291) 1s
+ok: run: logrotate: (pid 11299) 0s
+ok: run: mailroom: (pid 11306) 0s
+ok: run: nginx: (pid 11309) 0s
+ok: run: postgresql: (pid 11316) 1s
+ok: run: redis: (pid 11325) 0s
+ok: run: sidekiq: (pid 11331) 1s
+ok: run: unicorn: (pid 11338) 0s
+```
+
+To restart a component separately, you can append its service name to the
+`restart` command. For example, to restart **only** NGINX you would run:
+
+```bash
+sudo gitlab-ctl restart nginx
+```
+
+To check the status of GitLab services, run:
+
+```bash
+sudo gitlab-ctl status
+```
+
+Notice that all services say `ok: run`. If you get any weird results, like the
+unicorn service not starting, you may need to
+[reconfigure GitLab](#omnibus-gitlab-reconfigure) instead.
+
+### Omnibus GitLab reconfigure
+
+There may be times where you will be asked to _reconfigure_ GitLab. Remember
+that this method applies only for the Omnibus packages.
+
+Reconfigure Omnibus GitLab with:
+
+```bash
+sudo gitlab-ctl reconfigure
+```
+
+Reconfiguring GitLab should occur in the event that something in its
+configuration (`/etc/gitlab/gitlab.rb`) has changed.
+
+When you run this command, [Chef], the underlying configuration management
+application that powers Omnibus GitLab, will make sure that all directories,
+permissions, services, etc., are in place and in the same shape that they were
+initially shipped. This is where the _idempotency_ buzz-word you've been reading
+here and there fits.
+
+## Installations from source
+
+If you have followed the official installation guide to [install GitLab from
+source][install], run the following command to restart GitLab:
+
+```
+sudo service gitlab restart
+```
+
+The output should be similar to this:
+
+```
+Shutting down GitLab Unicorn
+Shutting down GitLab Sidekiq
+Shutting down GitLab Workhorse
+Shutting down GitLab MailRoom
+...
+GitLab is not running.
+Starting GitLab Unicorn
+Starting GitLab Sidekiq
+Starting GitLab Workhorse
+Starting GitLab MailRoom
+...
+The GitLab Unicorn web server with pid 28059 is running.
+The GitLab Sidekiq job dispatcher with pid 28176 is running.
+The GitLab Workhorse with pid 28122 is running.
+The GitLab MailRoom email processor with pid 28114 is running.
+GitLab and all its components are up and running.
+```
+
+This should restart Unicorn, Sidekiq, GitLab Workhorse and [Mailroom][]
+(if enabled). The init service file that does all the magic can be found in
+[`lib/support/init.d/gitlab`][src-service].
+
+---
+
+If you are using other init systems, like systemd, you can check the
+[GitLab Recipes][gl-recipes] repository for some unofficial services. These are
+**not** officially supported so use at your own risk.
+
+
+[omnibus-dl]: https://about.gitlab.com/downloads/ "Download the Omnibus packages"
+[install]: ../install/installation.md "Documentation to install GitLab from source"
+[mailroom]: ../incoming_email/README.md "Used for replying by email in GitLab issues and merge requests"
+[chef]: https://www.chef.io/chef/ "Chef official website"
+[src-service]: https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/support/init.d/gitlab "GitLab init service file"
+[gl-recipes]: https://gitlab.com/gitlab-org/gitlab-recipes/tree/master/init "GitLab Recipes repository"

doc/development/doc_styleguide.md

@@ -103,6 +103,17 @@ Inside the document:
   `_**Note:** This feature was introduced in GitLab EE 8.3_`. Otherwise, leave
   this mention out
 
+## References
+
+- There are many cases that a restart/reconfigure of GitLab is required. To
+  avoid duplication, link to the special document that can be found in
+  `doc/administration/restart_gitlab.md`. Usually the text will read like:
+
+    ```
+    Save the file and [reconfigure GitLab](../administration/restart_gitlab.md) for the changes to take effect.
+    ```
+  Replace `reconfigure` with `restart` where appropriate.
+
 ## API
 
 Here is a list of must-have items. Use them in the exact order that appears