Nut upsuser - Nov 2021 - Doing things before shutdown

What would be the preferred way to do some operations just before UPS is about
to lose its power? I need to shut down some remote devices which are connected
to the same UPS as my Nut server. They are not "NUT compatible" so I
need to prepare them for losing power with some scripts. The complete shutdown
of these devices takes about 120-150 seconds.

My first instinct was to call those scripts from the SHUTDOWNCMD. Then I
realised that Nut might ask UPS to shut down before that. But this could be
modified by offdelay in ups.conf, right?

Second thought was to NOTIFYCMD and upssched.conf with upssched-cmd script. And
catch the LOWBATT event there and call my shutdown scripts. Then I read that
even that could be interrupted by system (and UPS) shutdown, before letting
LOWBATT event to do it's magic.

Is it really so that there is no "safe" way to deal with notification
event LOWBATTERY? Will Nut start the shutdown procedure around same time when it
receives "[ob lb]" from UPS and it doesn't wait for LOWBATTERY
event to be processed? I know that in my setup UPS will have power for more than
180 seconds after reaching 20% battery level.

So is the only safe option to use ONBATT event and use START-TIMER method with
upssched.conf?

Cheers,

Kari

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On Mon, 15 Nov 2021, Kari Lempiainen wrote:
> What would be the preferred way to do some operations just before UPS is
about
> to lose its power? I need to shut down some remote devices which are
connected
> to the same UPS as my Nut server. They are not "NUT compatible"
so I need to
> prepare them for losing power with some scripts. The complete shutdown of 
> these devices takes about 120-150 seconds.
> 
> My first instinct was to call those scripts from the SHUTDOWNCMD. Then I 
> realised that Nut might ask UPS to shut down before that. But this could be
> modified by offdelay in ups.conf, right?
There are two approaches to shutting down on power failure: 1: wait until the 
UPS has reached LOWBATT status; 2: wait some number of seconds after ONBATT is 
detected.

Option 1 is simpler and is the most common.  However if you go this way, you 
take the risk of battery exhaustion before the remote devices have shut down. 
You can mitigate this by raising battery.charge.low using command upsrw if your 
UPS allows this.
> Second thought was to NOTIFYCMD and upssched.conf with upssched-cmd script.
> And catch the LOWBATT event there and call my shutdown scripts. Then I read
> that even that could be interrupted by system (and UPS) shutdown, before 
> letting LOWBATT event to do it's magic.
Option 2 using NOTIFYCMD is more complex to set up but will give you more 
assurance that the remote devices are shutdown correctly, particularly in the 
case of repeated power failures.
> Is it really so that there is no "safe" way to deal with
notification event
> LOWBATTERY?
Even if you use option 2, NUT is still capable of detecting [ob lb] and invoking
it's built-in shutdown procedure.  However this would only happen after 
excessive repeated power failures.
> Will Nut start the shutdown procedure around same time when it receives
"[ob
> lb]" from UPS and it doesn't wait for LOWBATTERY event to be
processed? I know
> that in my setup UPS will have power for more than 180 seconds after
reaching
> 20% battery level.
> 
> So is the only safe option to use ONBATT event and use START-TIMER method
with
> upssched.conf?
Option 2 is probably "safer" for shutting down remote devices, when
shutting
them down takes a significant part of the UPS survival time, but since it looks 
as if you have a sufficiently large UPS, try option 1, raise battery.charge.low 
and do lots of testing.

Roger