nfnl_osf - OS fingerprint loader utility
nfnl_osf -f fingerprints [ -d ]
The nfnl_osf utility allows to load a set of operating system signatures into the kernel for later matching against using iptables' osf match.
Exit status is 0 if command succeeded, otherwise a negative return code indicates the type of error which happened:
An up to date set of operating system signatures can be downloaded from http://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os .
The description of osf match in iptables-extensions(8) contains further information about the topic as well as example nfnl_osf invocations.