You will see the following messages at the bottom of output of the AL2QXVFB started task:
Starting Xvfb using server/display :8
Xvfb will be run in the background.
Run "ps -ef | grep Xvfb" to see process ID.
Should you see the message:
XVFB0178: Failed to establish all listening sockets
specify a different server/display number.