A million little bugs - hashcat dev

Especially if you have multilple GPUs under linux you came across the issue to adjust the fan speed.
The trick is to change the DISPLAY to the device you want to alter.

Example for two devices:
export DISPLAY=:0
aticonfig --pplib-cmd "set fanspeed 0 60"
export DISPLAY=:0.1
aticonfig --pplib-cmd "set fanspeed 0 60"

Thanks to d3ad0ne!