How to make Xvfb display visible?

I am running selenium through Xvfb on display number :99 like this:

/usr/bin/Xvfb :99 -ac -screen 0 1024x768x8 & export DISPLAY=":99" && java -jar /usr/lib/selenium/selenium-server-standalone-2.24.1.jar -port 4444

However display with number other than :0 is not visible by default. How do I make it visible to actually see what selenium is doing in the browser?

Solution

It's virtual. From the man page Xvfb(1):

Xvfb is an X server that can run on machines with no display hardware and no physical input devices. It emulates a dumb framebuffer using virtual memory.

Also in the man page:

Xvfb -pixdepths 3 27 -fbdir /var/tmp The server will listen for connections as server number 0, will have the default screen configuration (one screen, 1280x1024x8), will also support pixmap depths of 3 and 27, and will use memory mapped files in /var/tmp for the framebuffer.

xwud -in /var/tmp/Xvfb_screen0 Displays screen 0 of the server started by the preceding example.