The suspand action on critical battery seemed to stop working in this Ubuntu version. Instead my machine just shut down every time the battery was critical low.. without asking. That's horrible when you have documents open. Today I finally found the solution: pm-utils was missing.
But let me start from the beginning..
Beside the symptom that the laptop shuts down instead of suspending, the following things seemed a bit weird:
upower tells me that suspend is not possible:
$ upower -d
... < I stripped of the uninteresting outputs. Here is what matters: >
Don't get me wrong: Suspending is working when I just click on the suspend button. So I tried it via a dbus command:
$ dbus-send --system --print-reply --dest="org.freedesktop.UPower" /org/freedesktop/UPower org.freedesktop.UPower.Suspend
Error org.freedesktop.UPower.GeneralError: No kernel support
Now thats really weird. Than I found this on the internet: https://bbs.archlinux.org/viewtopic.php?id=147272&p=7
There they guess that upower still uses 'pm-is-supported' from the pm-utils package. Even though the upower package doesn't have this package as a dependency. So I installed it:
$ sudo apt-get install pm-utils
$ sudo reboot
And voilà: upower is saying that I'm now able to suspend and its working as critical low battery action as well. I hope this will help somebody out there who has the same problem ;)