-r n - REQUIRE flag - if the user has an ACUA record, they will be excluded if they do not have user-defined flag n set.
-c - renew time classes. You should have cron run the following
every day, preferably at a time that does not fall within any time class.
-d renew data
-t renew time (but not time classes)
Example Crontab Entry (/etc/crontab):
0 0 * * * root /usr/bin/acua renew -c -t
This means that at 12:00am (midnight) on every day, acua renew will
be ran.