[Nut-upsuser] UPS shutdown - always the thing to do?

Charles Lepple clepple at gmail.com
Tue Nov 20 03:57:33 UTC 2007

On Nov 19, 2007 9:28 PM, Whit Blauvelt <whit+nut at transpect.com> wrote:
> If so, that could leave a small window between the PC's going off and
> the UPS cutting the power (when not commanded to do so prematurely with that
> "shutdown" command) in which power restoration wouldn't trigger the PC
> rebooting - unless the UPS is smart enough to power cycle on power
> restoration just in the case that it was past the point of advising PC
> shutdowns already. If that's so, then I should stop worrying and get back to
> packing for vacation.

Generally speaking, when the UPS signals "on battery + low battery",
and the driver passes this back to NUT, the modified shutdown scripts
need to tell the UPS to pull power _after a delay_.

That delay is where the race condition can occur, and higher-end UPSes
are designed to cycle the output power even if the input power returns
during that window. The shutdown command to the UPS is considered a
"point of no return", in that case.

I can't speak specifically to the 1500AVR, but if the UPS is just
designed to provide a bit of backup power to shutdown a desktop
machine, it may not have all of the bells and whistles like
power-cycling the output after a shutdown+delay command.

- Charles Lepple

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