How do you run a GUI application without GUI (gui application as daemon on headless server)?

Okay, so I want to run a GUI application as daemon on a server without X. The application is a java program. It can be configured in a configuration file so the GUI is not necessary to use it. Unfortunately it doesn't have a shell executable.

I knew that one once, but forgot the solution. Basically there is a program which fakes an X-server to other programs. Finding that would be the ideal solution. Just can't remember what it was called.

I think you are referring to xvfb - the ability to run in a framebuffer.

or sudo apt-get install xvfb

You need to specify a resolution and colour depth as well as the nominal display number

Usage:

xvfb :1 -screen 0 800x600x8 &
export DISPLAY=":1"
java application_name.jar 

or shorter:

xvfb-run -a -e /tmp/some/log/file.log java -jar /home/user/somejava.jar

-a chooses a display number automatically, -e file specifies a logfile for error messages.