http://qkpm2ov2rjhjkhfsftskqho77uj5rewd5y44unkf6cb7tdhaxwcvh2id.onion/books/apc/APCUPSD%20User%20Manual.html
Please note that if you install from RPMs for a slave machine, you
will need to remove the changes that the RPM install script made
(similar to what is noted above) to the halt script. This is
because on a slave machine there is no connection to the UPS, so
there is no need to attempt to power off the UPS.