In /etc/init.d/nut.powerfail script is used /sbin/apcupsd as option to power off the machine but apcupsd is not part of sys-power/nut package. The original part of script is: elif [ -f /etc/apcupsd/powerfail ]; then UPS_CTL=/sbin/apcupsd UPS_POWERDOWN="${UPS_CTL} --killpower" that I have changed in: elif [ -f /etc/killpower -o -f /etc/nut/killpower ]; then UPS_CTL=/usr/sbin/upsmon UPS_POWERDOWN="${UPS_CTL} -c fsd" And works on my machine.
apcupsd seems to be only a fallback. See https://gitweb.gentoo.org/repo/gentoo.git/tree/sys-power/nut/files/nut.powerfail.initd Your proposal is basically in (first) fallback. But UPS_CTL is different. Could you explain, why upsmon instead of upsdrvctl?
