Troubleshooting and FAQ: MuJoCo, MediaPipe and ROS 2 in Docker

contact@mulhamfetna.com (Mulham Fetna) — Wed, 16 Sep 2026 00:00:00 +0000

Every entry here was hit, or deliberately checked, while building this project. Error messages are quoted exactly so a search for the message lands on the fix.

Camera and windows
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`RuntimeError: Failed to open camera at index 0`
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Something else holds the webcam — the standalone script, a previous container, a browser tab. Run docker compose down and close video apps. A camera opens in one process at a time.
The camera is another node. ls /dev/video*, then map that device and set CAMERA_INDEX (many webcams expose /dev/video0 for frames and /dev/video1 for metadata — use the first).
The device isn’t mapped. Check with docker compose config | grep video.

Windows don’t open — `cannot connect to X server`, `could not connect to display`
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Run ./setup_host.sh (it runs xhost +local:root). The permission resets when you log out.
Make sure echo $DISPLAY on the host prints :0, or export DISPLAY before docker compose up.
On Wayland, confirm XWayland is running: ls /tmp/.X11-unix/ should list X0.

Black, blank or garbled OpenCV window
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QT_X11_NO_MITSHM=1 must reach the container. It’s in the shared Compose environment — if a service defines its own environment:, it must merge the shared anchor with <<: *ros-env rather than replace it (Part 16).

Troubleshooting on Mulham Fetna

Troubleshooting and FAQ: MuJoCo, MediaPipe and ROS 2 in Docker

Camera and windows #

RuntimeError: Failed to open camera at index 0 #

Windows don’t open — cannot connect to X server, could not connect to display #

Black, blank or garbled OpenCV window #

Camera and windows
#

`RuntimeError: Failed to open camera at index 0`
#

Windows don’t open — `cannot connect to X server`, `could not connect to display`
#

Black, blank or garbled OpenCV window
#