[Nut-upsuser] Doing things before shutdown

[Kari Lempiainen]

> On 15. Nov 2021, at 16.09, Roger Price <roger at rogerprice.org> wrote:
> 
> 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.
> 

So basically Option 1 means setting FINALDELAY big enough to give time to do remote shutdowns. In my case something like 180. Option 2 is definitely more safe, that means using ONBATT and START-TIMER to figure out when to start remote shutdown.

The documentation regarding this shutdown procedure is not very clear in my opinion. It would be nice to see confirmation that just responding to LOWBATTERY event gives FINALDELAY amount of seconds to do shutdown actions.

Kari