[Nut-upsuser] Maybe this will make it to the FAQ :-)

Ciprian Marius Vizitiu cvizitiu at gbif.org
Sun Jun 24 20:59:13 UTC 2007

Hi Arjen,

I've just read the FAQ and got to the question: "Q: How can I make upsmon
shut down my system after some fixed interval?" Well it looked like the
question was there for me. :-)

You say:

Ask yourself this: why buy a nice big UPS with the matching battery and
corresponding runtime and then shutdown early?  If anything, I'd rather have
a few more minutes running on battery during which the power might return.
Once the power's back, it's business as usual with no visible interruption
in service.

If you purposely shut down early, you guarantee an interruption in service
by bringing down the box.

Although this sounds like a well considered argument it doesn't account for
all situations. It's not uncommon in certain parts of the world to have
power outages one after another with a say... 2 minutes in between. The
power company does its best to restore power but the consumption is still
too heavy so they need "a bigger hammer" :-)... I've seen it happening. In a
situation like this things can get hairy. Let's assume the UPS has juice for
25 minutes; let's assume it takes 40s to shut down and 1min 20s to boot. In
a scenario with the following events: "40 minutes power outage, power
restore for 2 minutes, power outage for 10 minutes, power restore" you might
end up having to manually say "Y" to fsck because the UPS has wasted all
juice on the first outage and there was no time to recharge the batteries
for the second outage... Chances are the machine is busy running scripts
before nut gets a chance to start and anyway the second power failure
strikes with no juice in the batteries. The other option is to shut down at
10 minutes after the first event so you have some 15 minutes left in the
UPS; even if the second event comes right when the machine is booting there
is enough juice for the machine to complete a boot->UPS-Alert->shutdown
cycle, don't you think?

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