X11 Error When Run as a Docker Container

Question

I'm trying to run an application from a Docker container which is supposed to open a GUI widow (a video stream in my case). The Docker container is run on a Raspberry Pi and I SSH into the Pi from my Mac and then I issue the Docker run command. I have one problem here:

When I run the whole thing as follows, it works flawlessly:

I run the command as:

docker run -it --net=host --device=/dev/vcsm --device=/dev/vchiq -e DISPLAY -v /tmp/.X11-unix joesan/motion_detector bash

From the bash, that opens up after issuing the Docker run command, I install xauth

root@cctv:/raspi_motion_detection/project# apt-get install xauth

I then add the Xauth cookie using Xauth add and then I then run my Python program which shows the GUI window with the video stream!

So far so good. But, every time I don't want to be doing these steps all over again. So I wrote a small script to do this as below:

HOST=cctv

DISPLAY_NUMBER=$(echo $DISPLAY | cut -d. -f1 | cut -d: -f2)
echo $DISPLAY_NUMBER

# Extract auth cookie
AUTH_COOKIE=$(xauth list | grep "^$(hostname)/unix:${DISPLAY_NUMBER} " | awk '{print $3}')

# Add the xauth cookie to xauth
xauth add ${HOST}/unix:${DISPLAY_NUMBER} MIT-MAGIC-COOKIE-1 ${AUTH_COOKIE}

# Launch the container  
docker run -it --net=host --device=/dev/vcsm --device=/dev/vchiq -e DISPLAY -v /tmp/.X11-unix  joesan/motion_detector`

But this time it fails with the error:

X11 connection rejected because of wrong authentication.
Unable to init server: Could not connect: Connection refused

I then tried to run the above script as a sudo user and I get the following:

xauth:  file /root/.Xauthority does not exist
xauth: (argv):1:  bad "add" command line
X11 connection rejected because of wrong authentication.
Unable to init server: Could not connect: Connection refused

Is there anything that I'm missing?

Answer 1

The apt-get install xauth command should only be required once, and so you can include it in your Dockerfile so that it gets executed when you build your image.

RUN apt-get install xauth

For the xauth add command, you seem to be depending upon the DISPLAY variable, which is passed on to the container on startup. In this case, it would be better to create a shell script which does all of the initialization that you need at startup, and then launches your Python program. For example:

#!/bin/bash

HOST=cctv
DISPLAY_NUMBER=$(echo $DISPLAY | cut -d. -f1 | cut -d: -f2)
AUTH_COOKIE=$(xauth list | grep "^$(hostname)/unix:${DISPLAY_NUMBER} " | awk '{print $3}')
xauth add ${HOST}/unix:${DISPLAY_NUMBER} MIT-MAGIC-COOKIE-1 ${AUTH_COOKIE}
python /path/to/program.py

Then, you can copy over this script during the build phase and set it as your command or entrypoint.

COPY init-script.bash /opt/program
CMD ["/bin/bash","/opt/program/init-script.bash"]

Answer 2

I solved this issue by using this command on the host before running the container:

xhost +

After that, I was able to run my container with:

sudo docker run -it --device=/dev/video0:/dev/video0 -e DISPLAY -v /tmp/.X11-unix:/tmp/.X11-unix test1

I didn't install xauth inside the container.