### Understand the alert

This alert is triggered when a `systemd service unit` enters the `failed state`. If you receive this alert, it means that a critical service on your system has stopped working, and it requires immediate attention.

### What is a systemd service unit?

A `systemd service unit` is a simply stated, a service configuration file that describes how a specific service should be controlled and managed on a Linux system. It includes information about service dependencies, the order in which it should start, and more. Systemd is responsible for managing these services and making sure they are functioning as intended.

### What does the failed state mean?

When a `systemd service unit` enters the `failed state`, it indicates that the service has encountered a fault, such as an incorrect configuration file, crashing, or failing to start due to other dependencies. When this occurs, the service is rendered non-functional, and you should troubleshoot the issue to restore normal functionality.

### Troubleshoot the alert

1. Identify the failed service unit

   Use the following command to list all failed service units:

   ```
   systemctl --state=failed
   ```

   Take note of the failed service unit name as you will use it in the next steps.

2. Check the service unit status

   Use the following command to investigate the status and any error messages:

   ```
   systemctl status <failed_service_unit>
   ```

   Replace `<failed_service_unit>` with the name of the failed service unit you identified earlier.

3. Examine the logs for the failed service

   Use the following command to inspect the logs for any clues:

   ```
   journalctl -u <failed_service_unit> --since "1 hour ago"
   ```

   Adjust the `--since` parameter to view logs from a specific timeframe.

4. Resolve the issue

   Based on the information gathered from the status and logs, try to resolve the issue causing the failure. This can involve updating configuration files, installing missing dependencies, or addressing issues with other services that the failed service unit depends on.

5. Restart the service

   Once the issue has been addressed, restart the service to restore functionality:

   ```
   systemctl start <failed_service_unit>
   ```

   Verify that the service has started successfully:

   ```
   systemctl status <failed_service_unit>
   ```

### Useful resources

1. [Systemd: Managing Services (ArchWiki)](https://wiki.archlinux.org/title/Systemd#Managing_services)
2. [Troubleshooting Systemd Services (Digital Ocean)](https://www.digitalocean.com/community/tutorials/how-to-use-systemctl-to-manage-systemd-services-and-units)
