Setting up dual external monitors on Ubuntu 9.04 (RandR 1.2)

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So I received my new T500 the same week that Ubuntu 9.04 is out and it ends up being the first distro on my laptop and my first task is to set up my dual external screens. Well, what worked last time (using ATI Catalyst) didn't seem to work this time. Installing Catalyst brought the second monitor to life but only as a clone to the first monitor, and the Multi-Display section of Catalyst is disabled, although both screens are correctly identified by Catalyst.

The problem ends up to be RandR 1.2 which disables some features in ATI Drivers (and perhaps Nvidia too). So, if you want to disable RandR to work with the proprietary drivers you have to modify to files:
1. In /etc/ati/amdpcsdb add the following line under [AMDPCSROOT/SYSTEM/DDX]:

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EnableRandR12=Sfalse

2. in /etc/X11/xorg.conf add the following line under "Device":

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Option      "EnableRandR12" "false"

After rebooting your computer the Multi-Display section in Catalyst will be enabled and you will be able to set up the big desktop.

This is actually isn't specific to Ubuntu as more distributions should start using RandR 1.2 soon.