I recently put Debian Lenny on my Powermac G5. So far it’s been ok but after upgrading to Squeeze the Mac went into vacuum cleaner mode: running the fans at full speed – very annoying. Turns out the necessary thermal modules weren’t getting loaded anymore because initramfs-tools was broken. The necessary module is different on each model of Mac and since I have model PowerMac7,2, I needed therm_pm72:
modprobe therm_pm72 echo "therm_pm72" >> /etc/modules
Fix the actual problem
Update initramfs-tools/hooks/thermal with the following patch.