In order to prevent intruders from resetting their system clocks in
order to continue to use expired tickets, Kerberos V5 is set up to
reject ticket requests from any host whose clock is not within the
specified maximum clock skew of the KDC (as specified in the
kdc.conf file). Similarly, hosts are configured to reject
responses from any KDC whose clock is not within the specified maximum
clock skew of the host (as specified in the
krb5.conf file). The
default value for maximum clock skew is 300 seconds, or five minutes.
MIT suggests that you add a line to client machines'
/etc/rc files to synchronize the machine's clock to your KDC at
boot time. On UNIX hosts, assuming you had a kdc called
kerberos in your realm, this would be:
gettime -s kerberos
If the host is not likely to be rebooted frequently, you may also want to set up a cron job that adjusts the time on a regular basis.