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I have nut which installed on Debian 8 host. The host is connected with UPS. In general everything works as expected. If UPS works on line, upsc shows the corresponding status. If UPS works on battery, upsc again shows the corresponding status. But if UPS has low battery status, upsc shows the corresponding status and (!) host shuts down even if I haven't asked nut for such behaviour.

Which part of nut (upsmon, upssched, or something else) is responsible for such behaviour?

  • Sounds like you should look at all the various configuration files including nut.conf and the config file for the ups package. – mdpc Nov 21 '16 at 21:53
  • Read the user manual pdf. /etc/ups/upsmon.conf is where you config what to do on low battery. – meuh Nov 22 '16 at 13:48
  • @meuh, thanks, I've found that setting of FINALDELAY from /etc/ups/upsmon.conf to large number can be workaround. Also I can prevent shut down by changing SHUTDOWNCMD. But I can't realize why nut shutdown my host even if I have not asked about this? Another words: does nut has variable like SHUTDOWN_IF_LOW_BATTERY 0|1? – Gluttton Nov 22 '16 at 15:19
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In the Network UPS Tools User Manual pdf, section 6.3.1 Shutdown design, it describes the algorithm used. The important point is that if the ups is on battery, and also the battery charge is low, this is critical, and means that soon there will be no power at all, so a shutdown is started.

On low battery, upsmon sets "FSD" (forced shutdown sequence), generates a NOTIFY_SHUTDOWN event, waits FINALDELAY seconds, creates the POWERDOWNFLAG file /etc/killpower, calls SHUTDOWNCMD. These values are set in /etc/ups/upsmon.conf.

On some ups devices, you can change the value of the low battery signal point. To list the variables for, say, device myups:

$ upsrw myups
[battery.charge.low]
Remaining battery level when UPS switches to LB (percent)
Type: STRING
Maximum length: 5
Value: 20
...

This example shows low battery is signalled when 20% charge is left. To change this to 10% you need the nut user and password you configured in /etc/ups/upsd.users, then you can do, eg:

$ upsrw -u mynutuser -p mynutpassword -s battery.charge.low=10 myups
OK

$ upsrw myups | grep -A4 battery.charge.low
[battery.charge.low]
Remaining battery level when UPS switches to LB (percent)
Type: STRING
Maximum length: 5
Value: 10

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