For the GUI to work properly it and the guiServer should be running.
The guiServer executable should be running on your "head node".  It does
NOT need to run as root (in fact, for security reasons, it SHOULD NOT).  It
is started with an (optional) TCP communications port number as an argument:

        guiServer/src/guiServer [PORT#]

The GUI itself can be run anywhere that has a screen, Java, and TCP network
access to the port specified above.  It is run as a ".jar" file:

        java -jar gui/dist/gui.jar

For more detailed information go to the top level of the GUI documentation 
in "doc/intro.html".