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Use DRM modetest to identify a connected display and test a supported mode.
Connect to the target through SSH and run target commands from the root shell. For instructions, see Sign in using SSH.

1. Make the root file system writable

Remount the root file system as writable to save the test output:

2. Stop Weston

Stop Weston and its socket so modetest can control the display:

3. Identify the connector and mode

Save the connector IDs and supported modes:
View the saved output:
Note the ID of a connector marked connected and one of its listed modes.

4. Copy the output to the host (optional)

To inspect or share the file from the host PC, open a new host terminal and run this command. Replace <device-ip> with the target’s IP address and <host-directory> with a local destination directory.

5. Test the selected mode

In the target SSH session, replace <connector-id> and <mode-name> with the values from step 3:
For example, if connector 32 supports 1920 × 1080 at 60 Hz:
Confirm that a test pattern appears on the connected display. Ignore the Failed to set gamma: Function not implemented warning if it appears.
Figure: DRM modetest output

6. End the test and restore Weston

Press Ctrl+C in the terminal running modetest to end the test.
After the test, follow Relaunch Weston to restore the desktop.