improper APM settings chosen when power status cannot be determined

[Antoine Pitrou]

On my *desktop* machine, on_ac_power returns 255 as a status code, which according to the man page means "Power status could not be determined". This is reasonable, but unfortunately /etc/apm/event.d/20hdparm takes it (*) as meaning "use the conservative setting" which sets the hard drive to spin down after 90 seconds of inactivity. This is entirely inappropriate for a desktop machine, as now I have to wait several seconds each time I access my non-system hard drive.

/etc/apm/event.d/20hdparm should really take 255 to mean "this is unlikely to be a battery-powered machine at all, don't mess with the power management settings".

(*) relevant snippet:

choose_power ()
{
    if on_ac_power > /dev/null
    then
 power_performance
    else
 power_conserve
    fi
}

[Antoine Pitrou (pitrou)]

Note the aforementioned file is part of the hdparm package, which is reasonable to install on a desktop machine:

$ dpkg -S apm/event.d/20hdparm
hdparm: /etc/apm/event.d/20hdparm

[Antoine Pitrou (pitrou)]

I'm entirely sure about the diagnosis, since it seems the configuration is conditioned on APMD_DRIVES (does it get a default value when the script is being run?). What I know is that, since Ubuntu 15.04, my HDD has been showing this behaviour of spinning down quite quickly while it didn't before...