If you are Nomachine and GNU Screen user, have you been annoyed by the problem that you can't start GUI program in a screen session? The reason to the problem is that the environment variable DISPLAY is not properly set when you attach a screen session. There are two posts talking about how to update environment variables such as SSH and DISPLAY  to make the life much easier.

http://samrowe.com/wordpress/ssh-agent-and-gnu-screen/

http://alan.lamielle.net/2009/03/09/environment-variables-and-gnu-screen