[Nut-upsuser] NUT & UPS, how to shut down client after 2 min on battery?

[Matt Kinni]

On 2022-12-22 05:47, Rafael Reinoso via Nut-upsuser wrote:
> I do not know much about NUT, but after some Googling, one idea I have 
> is to in /etc/nut/upsmon.conf on client change to this
> 
> |NOTIFYCMD "/etc/nut/shutdown_script.sh" NOTIFYFLAG ONBATT EXEC |
> 
> And then in /etc/nut/shutdown_script.sh have something like this
> 

Hi Raffe, I had a very similar setup to this for a long time until I 
recently changed it; I will describe what I used to do and why I don't 
set a timer like this anymore.

In /etc/ups/upsmon.conf (my system is Fedora) I captured three events:
    NOTIFYFLAG ONLINE   SYSLOG+EXEC
    NOTIFYFLAG ONBATT   SYSLOG+EXEC
    NOTIFYFLAG LOWBATT  SYSLOG+EXEC
    NOTIFYCMD /usr/sbin/upssched

The key thing here is I am not calling a bash script directly with 
NOTIFYCMD, but delegating it to the built in upssched process which has 
timer functionality (and is packaged with nut in Fedora).

In /etc/ups/upssched.conf, the key options are:
    CMDSCRIPT /usr/local/bin/upsmon-execscript.sh
    AT ONBATT * START-TIMER shutdown_onbatt 600
    AT ONLINE * CANCEL-TIMER shutdown_onbatt

As you can see it starts a 10 minute timer, and cancels the timer if 
mains power is restored.  The bash script is similar to yours, but 
benefits from not having to do any time management of its own or count 
how long it has been running.  upssched does that for you, and simply 
calls your script when the listed events occur and with the timer of 
your choosing.

Here is the problem with this approach in general:
  - what happens if I boot my server while already on battery, and
    the battery is low?  My script won't do anything for 10 minutes
  - what happens if the power repeatedly cycles on/off/on/off?
    10 more minutes are granted every time, which again leaves you
    in a dangerous situation

My current approach is to have my server turn off when the UPS hits 40% 
battery.  I have redefined the "lowbatt" signal to a very comfortable 
40%, so there is plenty of time to shutdown and still plenty of battery 
left for charging other things like my cellphone etc.

The way to accomplish this is in /etc/ups/ups.conf, under your ups 
configuration put:
    ignorelb
    override.battery.charge.low=40

This seems safer to me because it's based on the actual capacity 
remaining, and not an arbitrary timer.

Hope this helps, and happy new years!
Matt