Enabling SLI Technology in Ubuntu 9.04

Getting SLI technology working with Ubuntu 9.04 is a bit wierd to know, yet hopefully in later versions we shouldn't have to keep doing this :) ANYWAY follow these seteps.

You have tried typing "startx" and that didn't work, and you still at command prompt and wondering what to do now... Try this :)

Enabling SLI

0) Backup your old Video configuration just for convience

cp /etc/X11/xorg.conf /home/youraccount/xorg.conf-bk

So if that worked before you can restore it back.

1) Find the BusID address to the first PRIMARY card

lspci

An output of the above commad is

04:00.0 VGA compatible controller: nVidia Corporation G70 [GeForce 7600 GS] (rev a1)
06:00.0 VGA compatible controller: nVidia Corporation G70 [GeForce 7600 GS] (rev a1)

2) make note of BusID of primary (first) graphics card

e.g. 04:00:00 (last 0 might not be shown but need it anyway)

3) Generate a new Video configuration file

sudo nvidia-xconfig
enter password

You will be brought back to a new prompt.

4) Edit the Video configuration file to enable SLI technolgoy

sudo nano /etc/X11/xorg.conf

go to EndSection of Devices section
press Enter
press up arrow once
Type BusID "04:00:00"
Press Enter
Type Option "SLI" "Auto"
press ctrl o to save
press ctrl x to exit

The section should look something like this (Red is the new two lines added)

Section "Device"
Identifier     "Device0"
Driver         "nvidia"
VendorName     "NVIDIA Corporation"
    BusID          "04:00:00"
    Option         "SLI" "Auto"
EndSection

5) Verify the configuration works

startx

Then open up a terminal window and then type

nvidia-settings

Click on the "screen0"section, it should saying in the "GPUs" section something like

GeForce 7600 GS (GPU 0),
GeForce 7600 GS (GPU 1)

Enjoy :)

Addtional
You may try a different option in the device section of the video configuration file.

Off : As in OFF, don't use the SLI technology.
Auto : auto-select rendering option
SFR : Split Frame Rendering
AFR : Alternate Frame Rendering
AA : Anti Aliasing.
AFRofAA : Alternate Frame Rendering of Anti Aliasing (!?!? not sure of this one haven't tried it)

Personal Note: I believe "auto" maybe better as the device would then pick which RENDER is best for any current situation.

Further Reading
Wikipedia
Ubuntu Forums