Network UPS Tools (NUT) on Debian

nut.conf

MODE=standalone

sudoers

# Allow nut group to execute shutdown command
%nut	ALL=NOPASSWD: /sbin/shutdown

ups.conf

# Set maxretry to 3 by default, this should mitigate race with slow devices:
maxretry = 3

[eaton]
	driver = usbhid-ups
	port = auto
	vendorid = 0463

upsd.users

[upsmon]
	password = 1234
	upsmon master

upsmon.conf

MONITOR eaton@localhost 1 upsmon 1234 master

NOTIFYCMD /sbin/upssched
NOTIFYFLAG ONLINE SYSLOG+EXEC
NOTIFYFLAG ONBATT SYSLOG+WALL+EXEC
NOTIFYFLAG LOWBATT SYSLOG+WALL+EXEC

MINSUPPLIES 1
SHUTDOWNCMD "/sbin/shutdown -h +0"
POLLFREQ 5
POLLFREQALERT 5
HOSTSYNC 15
DEADTIME 15
POWERDOWNFLAG /etc/killpower
RBWARNTIME 43200
NOCOMMWARNTIME 300
FINALDELAY 5

upssched-cmd

#! /bin/sh
#
# This script should be called by upssched via the CMDSCRIPT directive.
# 
# Here is a quick example to show how to handle a bunch of possible
# timer names with the help of the case structure.
#
# This script may be replaced with another program without harm.
#
# The first argument passed to your CMDSCRIPT is the name of the timer
# from your AT lines.

case $1 in
	onbattwarn)
		sudo /sbin/shutdown -h +5
		logger -t upssched-cmd "The UPS is on battery power"
		;;
	ups-back-on-power)
		sudo /sbin/shutdown -c
		logger -t upssched-cmd "The UPS is back on wall power"
		;;
	*)
		logger -t upssched-cmd "Unrecognized command: $1"
		;;
esac

upssched.conf

CMDSCRIPT /usr/local/bin/upssched-cmd
PIPEFN /var/run/nut/upssched.pipe
LOCKFN /var/run/nut/upssched.lock
AT ONBATT * EXECUTE onbattwarn
AT ONLINE * EXECUTE ups-back-on-power

See also https://www.kepstin.ca/blog/networkupstoolsnutandsystemd/