[CentOS] Dual NVidia cards, dual monitors

Mon Jun 4 21:23:17 UTC 2012
Steven Chall <stevec at renci.org>

I've just installed CentOS 6.2 on an HP xw8600 with two NVidia GeForce 8800 GT video cards in it.  I have two Dell monitors than ran configured as a single contiguous desktop when this was a Windows 7 machine.  I've only been able to access one of the two monitors under CentOS, although the system demonstrates some awareness of the second GPU/monitor, because the second monitor shows the standard CentOS 6 image while the machine is running.  In addition, when it's starting up or shutting down a large wait cursor is displayed in that second monitor, and also shows the message "shutting down..." when that's going on.  However, the Display applet in the System | Preferences panel menu shows only the one monitor, and hitting the Detect Monitors button doesn't help.  Just to test the obvious, I switched the DVI cables coming out of the two video cards and as you'd expect what shows in the two monitors is also switched.

When I do an lspci at the command line I see at the bottom of the listing:

60:00.0 VGA compatible controller: nVidia Corporation G92 [GeForce 8800 GT] (rev a2)
80:00.0 VGA compatible controller: nVidia Corporation G92 [GeForce 8800 GT] (rev a2)

And the output from xrandr is:

Screen 0: minimum 320 x 200, current 2560 x 1600, maximum 8192 x 8192
DVI-I-3 connected 2560x1600+0+0 (normal left inverted right x axis y axis) 646mm x 406mm
   2560x1600      59.9*
   1280x800       59.9
DVI-I-4 disconnected (normal left inverted right x axis y axis)

I've done some considerable googling, and haven't found any discussions that offer a solution for my situation (dual video cards).  I did see the following from almost two years ago saying X  Windows just doesn't support it:

>From http://permalink.gmane.org/gmane.comp.freedesktop.libdlo/448, Bernie Thompson says (on October 13, 2010):

<begin quote>

On Wed, Oct 13, 2010 at 1:44 AM, Christoph Rissner <c.r at ...<http://gmane.org/get-address.php?address=c.r%2dxV8MHogwf5Dk7%2b2FdBfRIA%40public.gmane.org>> wrote:

> I think I've read somewhere that even XRandR 1.3 isn't up to multi GPU

> environments, so I guess Xinerama is the only option here.

Yes, unfortunately that's the fundamental problem.


I really only understand the low-level stuff (framebuffer driver), but

here's my understanding ...

The plumbing isn't there in X to support multiple graphics cards the

way Windows has since Win 98.

The main low-level features xorg needs are in the area of things like

"GPU object" and "shatter" support to allow screens to be split across


Right now, with RandR hand-config, you can get multiple X screens

[can't drag windows between them], one per-GPU, each of which can have

multiple monitors connected if that particular GPU reports multiple

outputs. With GPU object support, rendering could span GPUs and

several GPUs could be merged into one X screen similar to the

classical Xinerama setup.

<end quote>

So is this [still] the case?  Is Xinerama a viable alternative?  I'd also appreciate some help with the "RandR hand-config" that Bernie mentions.  Thanks for any info you may be able to provide.

-Steve Chall
 Senior Research Software Developer
 Renaissance Computing Institute (RENCI)
 Phone: 919-681-9639
 Email: stevec at renci.org<mailto:stevec at renci.org>