Expiring passwords
From FreeBSDwiki
You can force a change of password, and warn about the upcoming change, by adding
:passwordtime=90d:\ :warnpassword=5d:\
to your login.conf file in /etc.
- dont forget to run cap_mkdb /etc/login.conf
You may also be interested in this article: http://www.nas.nasa.gov/Groups/Security/epasswd/article.html and this section of the Manual Pages: http://www.freebsd.org/cgi/man.cgi?query=login.conf&sektion=5