Find a free X11 display number

Question

I have some unit tests that need an X11 display so I plan to start Xvfb before running them, but to start Xvfb I will need a free display number to connect it to. My best guess

Answer 1

Possibly a bit off-topic, but if you use xvfb-run to start your Xserver-needing command, then just running

# xvfb-run -a your command

does the trick.