I'm running Ubuntu 9.10 on my server. It works fine, it's just that over time (usually a couple of days) the memory usage just grows and grows until it invariably runs out and needs to be rebooted.

It's running Apache, Samba, ProFTPd, Postfix, Munin & Webmin. 

Is there anything that can be done to free up the memory that it doesn't need anymore?