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

Arjen de Korte nut+users at de-korte.org
Mon Jun 25 06:52:34 UTC 2007

Ciprian Marius Vizitiu wrote:

> 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.

I didn't say this, I was referring to the FAQ and the part that was
right before your quote:

>     If your system has a really complicated shutdown procedure, you
>     might need to shut down before the UPS raises the low battery flag.
>     For most users, however, the default behavior is adequate.

In my (private) reply, I wrote that you need to setup 'upssched', a
remark you also conveniently left out. You never mentioned anything
about repeating power failures.

> 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?

Read 'docs/shutdown.txt', especially the last part, 'One more tip'.

Best regards, Arjen

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