### Understand the alert

This alert is triggered when a `systemd device unit` enters a `failed state`. If you receive this alert, it means that a device managed by `systemd` on your Linux system has encountered an issue and is currently in a non-operational state.

### What is a systemd device unit?

`Systemd` is a system and service manager for Linux operating systems. A `device unit` in `systemd` is a unit that encapsulates a device in the system's device tree (e.g., `/sys` directory). The device units are used to automatically discover and manage devices present on the system.

### What does a failed state mean?

A `failed state` implies that the device has encountered an issue and is currently non-operational. The problem could be related to hardware, driver, or configuration issues.

### Troubleshoot the alert

1. Identify the failed device unit:

   Check the `systemd` status for failed units using the following command:

   ```
   systemctl --failed --type=device
   ```

   This will show you the list of device units that are currently in a failed state.

2. Check logs for errors:

   Use the `journalctl` command to check the logs for any error messages related to the failed device unit. For instance, if the failed unit is `example.device`, you can execute:

   ```
   journalctl -xe -u example.device
   ```

   This will show you the logs with any error messages that will help you identify the root cause of the failure.

3. Fix the issue:

   Depending on the results from the previous steps, you might need to:

   - Check the hardware connections and make sure they are properly connected.
   - Update or reinstall the device driver.
   - Check and correct device configurations if needed.

4. Restart the device unit:

   Once the issue has been fixed, restart the device unit using `systemctl`:

   ```
   sudo systemctl restart example.device
   ```

   Replace `example.device` with the specific device unit name.

5. Validate the fix:

   Check if the device unit is now operational by executing the following command:

   ```
   systemctl status example.device
   ```

   This should show you that the device unit is now active and running properly.

### Useful resources

1. [Systemd Device Units](https://www.freedesktop.org/software/systemd/man/systemd.device.html)