Script from https://www.jann.cc/2014/09/06/sandboxing_proprietary_applications_with_docker.html

dockapp

#!/bin/bash

# Initialize variables
resolution="1024x780x24"
additional_cmd="ls -l"
x11vnc_args=""
unixsockonly=0

while getopts "h?r:a:x:fu" opt; do
    printf " -%s '%s'\n" $OPTION $OPTARG
    case "$opt" in
    h|\?)
        help
        exit 0
        ;;
    r)  resolution=$OPTARG
        ;;
    a)  additional_cmd=$OPTARG
        ;;
    f)  x11vnc_args+="-forever "
        ;;
    u)  unixsockonly=1
        ;;
    esac
done

shift $((OPTIND-1))

help() {
  echo "./dockapp-start [arg...]"
}

echo "resolution='$resolution'"
echo "cmd='$cmd'"
echo "x11vnc_args='$x11vnc_args'"
echo "leftovers: $@"

# start framebuffer display server
Xvfb :1 -extension GLX -screen 0 $resolution &

# export DISPLAY or you have to use "DISPLAY=:1 /usr/bin/cmd"
export DISPLAY=:1

/usr/bin/openbox-session &

# Wait a bit until the X server is ready
sleep 1

# Launch an additional command in the background
$additional_cmd &

# Launch an xterm
xterm &

# Without using the -forever flag the container will stop
# as soon as vncviewer disconnects
#x11vnc -usepw -display :1 -forever

if [ $unixsockonly -eq 0 ]; then
    x11vnc -usepw -display :1 $x11vnc_args
else
    # switch to user app so that the socket gets created
    # with the correct user:group on the host
    su app -c"/x11vnc-0.9.13/x11vnc/x11vnc -unixsockonly /share/x11vnc-socket -display :1 $x11vnc_args"
fi

# To make sure we can restart this container properly
# Fatal server error: Server is already active for display 1
# If this server is no longer running, remove /tmp/.X1-lock
rm /tmp/.X1-lock