On 03/20/2013 12:41 PM, Fred Smith wrote: > I recall, from reading docs in either nut, or the apc package for > linux (don't recall which) that many USB UPSes do have signalling > between the UPS and the computer to tell the UPS to shut itself off > when the system has gone offline. So, I've been assuming that's what > is happening in my case. That's handled by /etc/init.d/halt. It only happens if you have nut or APC's software installed and configured. Take a look at the script, it's the last thing that happens if UPS management software is present. If not, then the system will try kexec or halt.