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

Based in the answer of @karunski.

Using Xvfb to probe the displays, and lsof to check if are unix sockets in the Xvfb process, is more effective, notice the sleep 0.5, can be variable depends on the machine.

#!/bin/bash
DISPLAY=0

until [ $DISPLAY_NUM > 10 ]; do
        echo -n "Looking for display on $DISPLAY..."
        Xvfb :$DISPLAY > /dev/null 2>&1 &
        pid=$!
        sleep 0.5
        lsof -a -U -p $pid  > /dev/null 2>&1    

        notfound="$?"
        kill $pid > /dev/null 2>&1

        wait $pid

        [ "$notfound" == "0" ] && echo "found" && break

        echo "fail"
        let DISPLAY=DISPLAY+1
done