[How-To] Overclocking ATI cards in LinuxLink goes to an article on Overclock.net. tl;dr version:
$ aticonfig –od-enable$ aticonfig –odsc
For example. to overclock at 800 for gpu, and 1000 for ram, on chips 0 and 1: $ aticonfig –odsc 800,1000 –adapter 0,1
Tip: Overclocking dual-GPU cards (e.g., ATI 5970) individually:
Use –adapter=0,1 for first card, –adapter=2,3 for second card, etc.
If using poclbm, can use -d n instead of DISPLAY=:n.n
Tip: To set fanspeed to 80:
aticonfig –pplib-cmd ‘set fanspeed 0 80''