Once you have the config files under ${SYSCONFDIR}/nut set up properly, the
following block can be added to your /etc/rc.local file to start nut.

# Start Nut
if [ -x ${PREFIX}/bin/upsdrvctl ]; then
    echo -n ' nut'
    ${PREFIX}/bin/upsdrvctl start > /dev/null 2>&1
    ${PREFIX}/sbin/upsd > /dev/null 2>&1
    ${PREFIX}/sbin/upsmon > /dev/null 2>&1
fi

You may also be interested in the "-i" flag to upsd, see upsd(8).