I was having all kids of issues trying to get a RETS server admin GUI display up and running. It uses java and the first error I was receiving from the command line was

Exception in thread "AWT-EventQueue-0" java.awt.HeadlessException: No X11 DISPLAY variable was set, but this program performed an operation which requires it.

I am sshing into the server with putty on Windows. The error above led me to download and install Xming. After downloading and installing I went to Putty > Connection > SSH > X11 > Click enable and set display location to

Still no dice. It wasn’t getting any error in putty window, but learned if you right click putty window > Event Log will give you tons of information. I found this gem:

2013-11-03 17:20:26 Remote debug message: No xauth program; cannot forward with spoofing.

of course, xauth wasn’t installed. I ran the follow to install and had gui up in no time.

yum search xauth
yum install xorg-x11-xauth

Another thing to look at is your sshd_config make sure you have the following set X11Forwarding yes