[Nut-upsuser] I am a bit confused

[Arjen de Korte]

Citeren durwin op mgtsciences.com:

> I understand now.  Not sure why a UPS has a 'shutdown' feature, but, it
> can't be shutdown before the machine has completed its shutdown.

It's not the command to shutdown that's important. Most drivers will  
at the same time also tell the UPS to switch back on when the power  
returns. This is important in unattended operations. Especially if the  
UPS is powering multiple systems, it helps in guaranteeing that  
everything gets a fresh start. If the power returns when the systems  
have already begun shutting down, powering down and restarting the UPS  
will then bring them back online without intervention. By letting the  
UPS run until the battery runs out, might mean that if the mains  
returns before that happens, the connected systems will not be  
restarted.

> Is this why the UPS has the variable,  ups.delay.shutdown ?

No. See below.

> Mine is set to 20.  I
> assume units are seconds.  Do I adjust it to account for the time my
> machine takes to shutdown?

Usually, the command to kill the output of the UPS is sent seconds  
before the machine switches off power (that's why the command must be  
sent from the system halt script, near the end). At that time the  
filesystems should be (re)mounted read-only so that the machine is  
ready to lose power immediately. So anything goes here, even a delay  
of as little as 1 second should work.

In the past people have requested that the UPS should wait until the  
hard disks have been stopped (spun down), fearing that killing power  
to them abruptly might damage them. For that reason, we delay  
switching off the UPS. I'm not convinced that this is a real problem  
or just FUD, but adding the delay doesn't hurt either.

If you feel your UPS should stay up longer after the system has  
shutdown, you can increase this value in some drivers. Since there  
isn't really a lot to gain here, many drivers will simply hardcode  
this to some fixed value.

Best regards, Arjen
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