ports/net-mgmt/arpwatch uses /usr/local/arpwatch for its data.
That's bad for NanoBSD that keeps /usr/local read-only.
Fix: The following patch makes it possible to build the package
for NanoBSD in the following way:
make ARPDIR=/var/arpwatch package
How-To-Repeat: Build NanoBSD with arpwatch from ports and boot.
arpwatch complains that /usr/local is read-only file system.