To set the system clock, use the date command.

For Redhat Systems, use the following format:
Code:
date --set="Mmm DD HH:MM:SS YYYY
Example:
Code:
date --set="Oct 20 15:52:29 2004"
For FreeBSD systems, use the following format:
Code:
date YYMMDDHHMM
Example:
Code:
date 0410201544
Will set the date/time to 2004, October 20th, 15:44 (3:44pm).