[Nut-upsuser] Synthesize low batt (LB) fron SNMP UPS which does not support this?

[Carsten Aulbert]

Hi,

after ignoring this for too long (see [1]), I'm still struggling how to 
shut down servers fed by two independent UPS systems. Both are connected 
to NUT via the snmp-ups driver with mibs "huawei" and "netvision".

However, I fear both do not feature the LB warning via ups.status.

We can shut down all less important servers (conencted to a single UPS) 
via upssched and a 30s timer after OB, but I still struggle hard to 
arrive at a working schema how to shut down more important servers based 
on remaining battery charge/projected run time and/or low batt warning.

Looking at clients/upsmon.c I think, without the flag ST_LOWBATT set for 
ups->status, MINSUPPLY will never truly be considered a usable threshold 
and thus I'm left with a machine which would not shutdown.

Thus, what would e the best way forward here?

* Try to patch the server to synthesize LB there? If so, any suggestion 
how to do this?

* Try to patch upsmon.c's is_ups_critical method to also include extra 
criteria, e.g. remaining run time/battery charge?

* Keep nut unpatched but use our own NOTIFYCMD or CMDSCRIPT to pull the 
values from the server and implement our logic there?

* Another way, I've overlooked?

Cheers and thanks a ton in advance for suggestions.

Carsten

[1] Message-ID: <f794644f-e3b8-3557-da63-bd19d88a7c03 at aei.mpg.de> from 
2022-12-05
-- 
Dr. Carsten Aulbert, Max Planck Institute for Gravitational Physics,
Callinstraße 38, 30167 Hannover, Germany, Phone +49 511 762 17185
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