Comment 4 for bug 49240

/sbin/on_ac_power is in powermgmt-base, so I'm reassigning this bug over there.

Of course the easiest and fastest case is to build the modules in the kernel; that's the case in jaunty but doesn't help hardy nor custom kernels.

On my system, the aforementioned modules are loaded automatically during boot even when not specified in /etc/default/acpid, so it's probably just a race that on_ac_power needs the modules loaded. I think on_ac_power could be improved to test for ACPI support and modprobe the relevant modules if the information is not present yet (just like we load modules to find the rootfs).