http://qkpm2ov2rjhjkhfsftskqho77uj5rewd5y44unkf6cb7tdhaxwcvh2id.onion/books/apc/APCUPSD%20User%20Manual.html
Solution This is a kernel bug and is most easily worked around by
not hot- unplugging the UPS while apcupsd is running. This issue
may be fixed in recent FreeBSD kernels. Platforms and Versions The *BSD USB driver supports FreeBSD, OpenBSD and NetBSD.