Originally Posted by AaronP
You can't drive the same graphics card with two different X servers at the same time.
Not entirely true.
The NVIDIA driver definitely makes it difficult, but it can be done.
At least I have achieved it with a VGA and a TV-OUT connection on the same card.
I have a Geforce 6200 card (VGA,DVI,TV-OUT), in an Athlon 2700+ (32bit). I am running Ubuntu 10.04 with the latest updates.
The trick it seems is to start both X servers as close in time as possible to one another.
From reading other posts, and from observing the behaviour myself, what seems to be happening when the NVIDIA driver loads up, is that it tries to grab all the video outputs for the current X server. Therefore the last X server that you run will grab all the video outputs regardless of whether or not it intends to use them.
If you start both X servers at the same time (or as close as possible), they both end up keeping the video output that they initially requested.
I've been running it for a few hours now and the results seem stable.
To make it easier on myself, I have written two simple bash scripts that wait until the other script is running before they start the X servers. This ensures both start very close together.
Its not perfect. There is some minor occasional video corruption on the VGA output but the TV-OUT seems fine and its definitely usable.
Still be nice if NVIDIA could fix this properly
Have gotten the right DVI cable today and have tested with the DVI Output. I can get DVI + TVOUT and DVI + VGA to work, but a three-seat system of DVI + VGA + TVOUT does not seem to work.
One additional pointer to get it working is that the DVI display seems to want to be started just before the TV-OUT display.
It seems though if you start the computer up with the DVI connected, then VGA + TVOUT stops working (error message : (EE) Oct 18 15:34:57 NVIDIA(0): Error setting DVC ), but its not really a huge problem.
One extra positive is that by using DVI+TVOUT instead of the VGA+TVOUT, it seems to fix the display corruption issue.