Thank you for your help!
In fact, I can't just forget about the simpler video card. I am dealing here with a Sun Fire X4440 server. The simpler video card is an onboard hardware that is used by its ILOM (an web remote management interface), so that I am able to remotely configure the server.
This server also has two Quadro FX 5600 PCI express video cards with 2 GPUs each. That means that I have 4 GPUs to configure and I should be able to start a remote session using VNC (and VirtualGL) on any of these GPUs (there should be a device configuration for each of them, as well as screen and screen layout as far as I understood).
So, my problem can not be simplified by removing the simpler video card... Just forgetting about VirtualGL for a moment, I would like to know how can I tell VNC server to start an X session using a given ServerLayout. I really didn't get this yet!
Originally Posted by jschiwal
You need to have the remote application's virtualgl use a different screen (on the remote server) than the one normally used. You need a "Device" section for each card. Each "Device" section needs a "BusID" entry.
You also need two "Screen" sections with Device entries for the respective cards. You have done this already.
You also need two "Screen" entries in your "Server Layout" section. This you don't have.
I don't know the details on how you indicate which remote screen that virtualGL will use at the remote application server. Normally the x-server on your local client computer will provide the display. You will need to find the answer in the virtualGL documentation.
The application servers xorg.conf file can have more than one "Server Layout" section. You might try starting an X instance using the -layout <layout identifier> option. Then the default layout doesn't need and entry for the second screen.
You may make life easier if you simply use the better video card.