Steps
Logged in as root, check which timezone your machine is currently using by executing `date`. You'll see something like Mon 17 Jan 2005 12:15:08 PM PST, PST in this case is the current timezone.
Change to the directory /usr/share/zoneinfo here you will find a list of time zone regions. Choose the most appropriate region, if you live in Canada or the US this directory is the "America" directory.
If you wish, backup the previous timezone configuration by copying it to a different location. Such as
mv /etc/localtime /etc/localtime-old
Create a symbolic link from the appropiate timezone to /etc/localtime. Example:
ln -s /usr/share/zoneinfo/Europe/Amsterdam /etc/localtime
If you have the utility rdate, update the current system time by executing
/usr/bin/rdate -s time.nist.gov
Set the ZONE entry in the file /etc/sysconfig/clock file (e.g. "America/Los_Angeles")
Set the hardware clock by executing:
/sbin/hwclock --systohc
Tips
On some versions of RedHat Linux, Slackware, Gentoo, SuSE, Debian, Ubuntu, and anything else that is "normal", the command to display and change the time is 'date', not 'clock'
On RedHat Linux there is a utility called "Setup" that allows one to select the timezone from a list, but you must have installed the 'redhat-config-date' package.
Warnings
Some applications (such as PHP) have separate timezone settings from the system timezone.
On some systems, there is a system utility provided that will prompt for the correct timezone and make the proper changes to the system configuration. For example, Debian provides the "tzsetup" or "tzconfig" utility.