Can you run GUI applications in a Docker container?

Question

How can you run GUI applications in a Docker container?

Are there any images that set up vncserver or something so that you can - for example - add an e

Answer 1

Sharing host display :0, as stated in some other answers, has two drawbacks:

• It breaks container isolation due to some X security leaks. For example, keylogging with xev or xinput is possible, and remote control of host applications with xdotool.
• Applications can have rendering glitches and bad RAM access errors due to missing shared memory for X extension MIT-SHM. (Can also be fixed with isolation degrading option --ipc=host).

Below an example script to run a docker image in Xephyr that addresses this issues.

• It avoids X security leaks as the docker applications run in a nested X server.
• MIT-SHM is disabled to avoid RAM access failures.
• Container security is improved with --cap-drop ALL --security-opt no-new-privileges. Also the container user is not root.
• An X cookie is created to restrict access to Xephyr display.

The script expects some arguments, first a host window manager to run in Xephyr, second a docker image, optionally third an image command to be executed. To run a desktop environment in docker, use ":" instead of a host window manager.

Closing Xephyr window terminates docker container applications. Terminating the dockered applications closes Xephyr window.

Examples:

• xephyrdocker "openbox --sm-disable" x11docker/lxde pcmanfm
• xephyrdocker : x11docker/lxde
• xephyrdocker xfwm4 --device /dev/snd jess/nes /games/zelda.rom

xephyrdocker script:

#! /bin/bash
#
# Xephyrdocker:     Example script to run docker GUI applications in Xephyr.
#
# Usage:
#   Xephyrdocker WINDOWMANAGER DOCKERIMAGE [IMAGECOMMAND [ARGS]]
#
# WINDOWMANAGER     host window manager for use with single GUI applications.
#                   To run without window manager from host, use ":"
# DOCKERIMAGE       docker image containing GUI applications or a desktop
# IMAGECOMMAND      command to run in image
#
Windowmanager="$1" && shift
Dockerimage="$*"

# Container user
Useruid=$(id -u)
Usergid=$(id -g)
Username="$(id -un)"
[ "$Useruid" = "0" ] && Useruid=1000 && Usergid=1000 && Username="user$Useruid"

# Find free display number
for ((Newdisplaynumber=1 ; Newdisplaynumber <= 100 ; Newdisplaynumber++)) ; do
  [ -e /tmp/.X11-unix/X$Newdisplaynumber ] || break
done
Newxsocket=/tmp/.X11-unix/X$Newdisplaynumber

# cache folder and files
Cachefolder=/tmp/Xephyrdocker_X$Newdisplaynumber
[ -e "$Cachefolder" ] && rm -R "$Cachefolder"
mkdir -p $Cachefolder
Xclientcookie=$Cachefolder/Xcookie.client
Xservercookie=$Cachefolder/Xcookie.server
Xinitrc=$Cachefolder/xinitrc
Etcpasswd=$Cachefolder/passwd

# command to run docker
# --rm                               created container will be discarded.
# -e DISPLAY=$Newdisplay             set environment variable to new display
# -e XAUTHORITY=/Xcookie             set environment variable XAUTHORITY to provided cookie
# -v $Xclientcookie:/Xcookie:ro      provide cookie file to container
# -v $NewXsocket:$NewXsocket:ro      Share new X socket of Xephyr
# --user $Useruid:$Usergid           Security: avoid root in container
# -v $Etcpasswd:/etc/passwd:ro       /etc/passwd file with user entry
# --group-add audio                  Allow access to /dev/snd if shared with '--device /dev/snd' 
# --cap-drop ALL                     Security: disable needless capabilities
# --security-opt no-new-privileges   Security: forbid new privileges
Dockercommand="docker run --rm \
  -e DISPLAY=:$Newdisplaynumber \
  -e XAUTHORITY=/Xcookie \
  -v $Xclientcookie:/Xcookie:ro \
  -v $Newxsocket:$Newxsocket:rw \
  --user $Useruid:$Usergid \
  -v $Etcpasswd:/etc/passwd:ro \
  --group-add audio \
  --env HOME=/tmp \
  --cap-drop ALL \
  --security-opt no-new-privileges \
  $(command -v docker-init >/dev/null && echo --init) \
  $Dockerimage"

echo "docker command: 
$Dockercommand
"

# command to run Xorg or Xephyr
# /usr/bin/Xephyr                an absolute path to X server executable must be given for xinit
# :$Newdisplaynumber             first argument has to be new display
# -auth $Xservercookie           path to cookie file for X server. Must be different from cookie file of client, not sure why
# -extension MIT-SHM             disable MIT-SHM to avoid rendering glitches and bad RAM access (+ instead of - enables it)
# -nolisten tcp                  disable tcp connections for security reasons
# -retro                         nice retro look
Xcommand="/usr/bin/Xephyr :$Newdisplaynumber \
  -auth $Xservercookie \
  -extension MIT-SHM \
  -nolisten tcp \
  -screen 1000x750x24 \
  -retro"

echo "X server command:
$Xcommand
"

# create /etc/passwd with unprivileged user
echo "root:x:0:0:root:/root:/bin/sh" >$Etcpasswd
echo "$Username:x:$Useruid:$Usergid:$Username,,,:/tmp:/bin/sh" >> $Etcpasswd

# create xinitrc
{ echo "#! /bin/bash"

  echo "# set environment variables to new display and new cookie"
  echo "export DISPLAY=:$Newdisplaynumber"
  echo "export XAUTHORITY=$Xclientcookie"

  echo "# same keyboard layout as on host"
  echo "echo '$(setxkbmap -display $DISPLAY -print)' | xkbcomp - :$Newdisplaynumber"

  echo "# create new XAUTHORITY cookie file" 
  echo ":> $Xclientcookie"
  echo "xauth add :$Newdisplaynumber . $(mcookie)"
  echo "# create prepared cookie with localhost identification disabled by ffff,"
  echo "# needed if X socket is shared instead connecting over tcp. ffff means 'familiy wild'"
  echo 'Cookie=$(xauth nlist '":$Newdisplaynumber | sed -e 's/^..../ffff/')" 
  echo 'echo $Cookie | xauth -f '$Xclientcookie' nmerge -'
  echo "cp $Xclientcookie $Xservercookie"
  echo "chmod 644 $Xclientcookie"

  echo "# run window manager in Xephyr"
  echo $Windowmanager' & Windowmanagerpid=$!'

  echo "# show docker log"
  echo 'tail --retry -n +1 -F '$Dockerlogfile' 2>/dev/null & Tailpid=$!'

  echo "# run docker"
  echo "$Dockercommand"
} > $Xinitrc

xinit  $Xinitrc -- $Xcommand
rm -Rf $Cachefolder

This script is maintained at x11docker wiki. A more advanced script is x11docker that also supports features like GPU acceleration, webcam and printer sharing and so on.