So the problem is that the computer running GPU programs do not have sufficient permission to access the X server on your GPU server.
You need to use xauth or xhost command to change the privilege settings.
Or you can simply pass -ac (no access control with xauth) parameter to the X server command line. However you may also need to use xhost to edit the white list of remote hosts.
That's why I have (in /etc/gdm/custom.conf):
command=/usr/bin/Xorg -br -ac -audit 0
You can't run xhost (as it needs someone already having authorization to the server). xauth is likewise not good.
It looks like the above 'command' line is perhaps ignored:
[veldema@faui21k X11]$ ps ax|grep Xorg
2618 tty7 Ss+ 0:03 /usr/bin/Xorg :0 -br -verbose -auth /var/run/gdm/auth-cookie-XX0CJFQU-for-gdm -nolisten tcp
9963 pts/1 S+ 0:00 grep Xorg
So it was ignored. Try to edit gdm.conf itself?
Or there is a simple way, just copy /var/run/gdm/auth-cookie-XX0CJFQU-for-gdm to your home directory and rename it to ".Xauthority".
Also, you can use fglrxinfo to check if the permission is sufficient.
Yep, that did the trick: I copied the /var/run/gdm/auth cookie
and now I once again have a FindDevices prog that works!
This should perhaps be put in the doc for remote CAL apps. Now writing a simple script to copy that file on startup to some public place so users can do 'xauth merge'