xvfb-run-safe

#!/bin/bash

if [ ! -x "`which xvfb-run 2> /dev/null`" ]; then
    echo "Need to install xvfb-run."
    exit 1
fi

# allow settings to be overridden via ENV vars
: "${XVFB_LOCKDIR:=$HOME/.xvfb-locks}"
: "${XVFB_DISPLAY_MIN:=99}"
: "${XVFB_DISPLAY_MAX:=599}"

# assuming only one user will be using this, place the locks in the home directory
# to avoid vulnerability to symlink attacks.
# if multiple users are to make use of this wrapper concurrently, you should write to /tmp instead
mkdir -p -- "$XVFB_LOCKDIR" || exit 2

i=$XVFB_DISPLAY_MIN
while ((i < XVFB_DISPLAY_MAX)); do
    if [ -f "/tmp/.X${i}-lock" ]; then # avoid an obvious open display
        ((++i))
        continue
    fi
    # this is an optional var to be used to understand what process uses this display
    # technically speaking, we could read the PID inside the lock file and then do some proc lookups but this is easier
    # if empty, the lock file name will just be the X display number
    if [ -n "$X_SESSION_NAME" ];then
	LOCK_NAME=${X_SESSION_NAME}_${i}
    else
	LOCK_NAME=$i
    fi
    exec 5> "$XVFB_LOCKDIR/$LOCK_NAME" || continue # open a lockfile
    if flock -x -n 5; then # attempt lock
        export X_SERVER_DISPLAY_NUM=$i               # export selected display for use in subsequent scripts
        exec xvfb-run --server-num="$i" "$@" || exit # once locked, run xvfb-run on selected display
    fi
    ((i++))
done