I need to run an X app in a VM which has almost nothing installed, not even "xauth". So the usual "ssh -X" does not work, as it requires xauth. However, I just learned that recent SSH can now do arbitary Unix port fowarding. So one can do

   ssh -R 6010:/tmp/.X11-unix/X0  user@host

and then do "export DISPLAY=localhost:10.0" on the VM, and things Just Work™. By forwarding to a TCP port, things like Qt are also tricked into not using /dev/shm/. If you forward to a Unix socket, it will try that and of course fail.

ssh, you are awesome!