SSH operations become slow as the number of users grows.
## The reason
OpenSSH searches for a key to authorize a user via a linear search. In the worst case, such as when the user is not authorized to access GitLab, OpenSSH will scan the entire file to search for a key. This can take significant time and disk I/O, which will delay users attempting to push or pull to a repository. Making matters worse, if users add or remove keys frequently, the operating system may not be able to cache the authorized_keys file, which causes the disk to be accessed repeatedly.
## The solution
GitLab Shell provides a way to authorize SSH users via a fast, indexed lookup to the GitLab database. GitLab Shell uses the fingerprint of the SSH key to check whether the user is authorized to access GitLab.
> **Warning:** OpenSSH version 6.9+ is required because `AuthorizedKeysCommand` must be able to accept a fingerprint. These instructions will break installations using older versions of OpenSSH, such as those included with CentOS as of May 2017.
Create this file at `/opt/gitlab-shell/authorized_keys`:
Confirm that SSH is working by removing your user's SSH key in the UI, adding a new one, and attempting to pull a repo.
> **Warning:** Do not disable writes until SSH is confirmed to be working perfectly because the file will quickly become out-of-date.
In the case of lookup failures (which are not uncommon), the `authorized_keys` file will still be scanned. So git SSH performance will still be slow for many users as long as a large file exists.
You can disable any more writes to the `authorized_keys` file by unchecking `Write to "authorized_keys" file` in the Application Settings of your GitLab installation.
![Write to authorized keys setting](img/write_to_authorized_keys_setting.png)
Again, confirm that SSH is working by removing your user's SSH key in the UI, adding a new one, and attempting to pull a repo.
Then you can backup and delete your `authorized_keys` file for best performance.
## How to go back to using the `authorized_keys` file
This is a brief overview. Please refer to the above instructions for more context.
1.[Rebuild the `authorized_keys` file](../raketasks/maintenance.md#rebuild-authorized_keys-file)
1. Enable writes to the `authorized_keys` file in Application Settings
1. Remove the `AuthorizedKeysCommand` lines from `/etc/ssh/sshd_config`
1. Reload sshd: `sudo service sshd reload`
1. Remove the `/opt/gitlab-shell/authorized_keys` file
| **CI_RUNNER_ID** | 8.10 | 0.5 | The unique id of runner being used |
| **CI_RUNNER_TAGS** | 8.10 | 0.5 | The defined runner tags |
| **CI_PIPELINE_ID** | 8.10 | 0.5 | The unique id of the current pipeline that GitLab CI uses internally |
| **CI_PIPELINE_SOURCE** | 9.3 | all | The variable indicates how the pipeline was triggered, possible options are: push, web, trigger, schedule, api, pipeline |
| **CI_PIPELINE_TRIGGERED** | all | all | The flag to indicate that job was [triggered] |
| **CI_PROJECT_DIR** | all | all | The full path where the repository is cloned and where the job is run |
| **CI_PROJECT_ID** | all | all | The unique id of the current project that GitLab CI uses internally |
If all items are green, then congratulations, the upgrade is complete!
### 13. Elasticsearch index update (if you currently use Elasticsearch)
In 9.3 release we changed the index mapping to improve partial word matching. Please re-create your index by using one of two ways listed below:
1. Re-create the index. The following command is acceptable for not very big GitLab instances (storage size no more than few gigabytes).
```
# Omnibus installations
sudo gitlab-rake gitlab:elastic:index
# Installations from source
bundle exec rake gitlab:elastic:index
```
1. For very big GitLab instances we recommend following [Add GitLab's data to the Elasticsearch index](../integration/elasticsearch.md#add-gitlabs-data-to-the-elasticsearch-index).
## Things went south? Revert to previous version (9.2)
msg='No GitLab Enterprise Edition license has been provided yet. Pushing code and creation of issues and merge requests has been disabled. Ask an admin to upload a license to activate this functionality.'
msg='No GitLab Enterprise Edition license has been provided yet. Pushing code and creation of issues and merge requests has been disabled. Ask an admin to upload a license to activate this functionality.'