Graphics with Xephyr fail to run on WSL2 / WSLg (read-only /tmp/.X11-unix)

[eyespore]

Problem Description

Since WSLg mounts /tmp/.X11-unix/ as read-only, so Xephyr cannot create its UNIX domain socket /tmp/X11-unix/X*. As a result, Xephyr automatically falls back to abstract sockets @/tmp/.X11-unix/X*:

Xephyr :110 &
# _XSERVTransmkdir: Mode of /tmp/.X11-unix should be set to 1777
# _XSERVTransSocketCreateListener: failed to bind listener
# _XSERVTransSocketUNIXCreateListener: ...SocketCreateListener() failed
# _XSERVTransMakeAllCOTSServerListeners: failed to create listener for unix

ss -lx | grep X110
# u_str LISTEN 0 4096 @/tmp/.X11-unix/X110 603055 * 0

However, x11docker does not seem to detect this fallback, so:

• DISPLAY remains set to :110
• containers cannot connect to the Xephyr server
• manual intervention is required (either TCP or socat bridging)

Workaround 1: Use --xoverip and manually fix DISPLAY

Test image:

FROM ubuntu:20.04
RUN apt-get update && apt-get install -y x11-apps

Launch Xephyr over TCP:

x11docker \
  --xephyr \
  --size=1280x720 \
  --network \
  --xoverip \
  --no-entrypoint \
  --display=110 \
  --env=DISPLAY=host:110 \
  -- --add-host=host:host-gateway -- \
  ubuntu:test xeyes

This allows simple X apps (xeyes xclock icewm) to run correctly.

Workaround 2: Bridge abstract socket using socat

Start Xephyr and dump the generated environment file:

x11docker \
  --xephyr \
  --size=1280x720 \
  --printenv=$HOME/.config/x11docker/xenv \
  --display=110 \
  --xonly
#Xephyr falls back to abstract unix socket: @/tmp/.X11-unix/X110

Bridge abstract socket ↔ file socket:

socat unix-listen:${HOME}/.config/x11docker/X110,fork,unlink-close \
  abstract-connect:/tmp/.X11-unix/X110

Then launch the container using the bridged socket:

eval $(sed 's/\([A-Z_]*=\)/\n\1/g' ~/.config/x11docker/xenv | tail -n +2)

x11docker \
  --hostdisplay \
  --no-entrypoint \
  -- -v ${HOME}/.config/x11docker/X110:/tmp/.X11-unix/X110 -- \
  ubuntu:test xeyes

This also works reliably for simple X applications.

Desktop environments still fail (maybe due to my setup?)

Running a full desktop environment (e.g., XFCE) still fails on WSL2:

x11docker \
  --xephyr \
  --size=1280x720 \
  --network \
  --xoverip \
  --desktop \
  --display=110 \
  --env=DISPLAY=host:110 \
  -- --add-host=host:host-gateway -- \
  x11docker/xfce

Typical errors:

Unable to launch "xfwm4": Failed to close file descriptor for child process (Operation not permitted)
Unable to launch "xfce4-panel": Failed to close file descriptor for child process (Operation not permitted)
Unable to launch "Thunar": Failed to close file descriptor for child process (Operation not permitted)
...

• --debug log is at: https://gist.github.com/eyespore/a7c95c4464de8acea9e85d089d8d873c
• --verbose log is at: https://gist.github.com/eyespore/ec3fda0a1d4b514829c77a000721505e

I'm not sure whether this is: an x11docker issue, a Xephyr limitation under WSL2 or simply my configuration problem. If you have any insight into whether full DEs are expected to work on WSL2 + Xephyr, that would be very helpful.

Summary

Since WSLg forces /tmp/.X11-unix/ into read-only mode, Xephyr always falls back to abstract sockets. At the moment, this requires manual fixes to make x11docker work.

Would it be possible for x11docker to:

• Detect WSL2 + read-only /tmp/.X11-unix
• If Xephyr falls back to abstract sockets, automatically switch to --xoverip, or automatically adjust DISPLAY (e.g., DISPLAY=host:110)
• Optionally check if socat is installed and automatically provide a bridged UNIX socket
• Warn users when desktop environments are unlikely to work under WSL2

These adjustments might make x11docker much smoother to use on WSL2/Xephyr setups.

Thanks a lot for your work on x11docker! I'd be happy to provide more logs or test patches if needed.

Environment

• Windows 10 WSL2 with WSLg enabled
• Distribution inside WSL2: Ubuntu 20.04
• Docker version: 27.1.1, build 6312585
• x11docker version: 7.7.2-beta