If you are using GNOME it it easy to keep the system clock synchronized with a
timeserver. Right mouse click on the clock and select
Adjust Date & Time.
Configure it to synchronize and Ubuntu will install the required packages. I run
an Ubuntu LAMP server without GNOME. Like I was, you might be wondering how to
keep your Ubuntu server’s clock set.
The easiest way is to install
sudo apt-get install ntp-simple
Once the install is finished ntpd will monitor the time and gradually correct any drift. This is perfect for servers where large jumps in the time could cause problems. Note that after installing ntpd, it could take a while for it to make the first correction.
You can read more about time synchronization in the Ubuntu server guide.