How to change time and/or timezone in CentOS

Generically, I use this

Change directory to /etc

[root@testbed ~]# cd /etc

Now create a symbolic link (aka symlink) to the timezone e.g. Asia/Karachi (for Pakistan standard time)

[root@testbed etc]# ln -sf /usr/share/zoneinfo/Asia/Karachi localtime
[root@testbed etc]# date
Mon Jan 16 19:26:52 PKT 2012

Please note that the timezone is following a directory-structure so if you want EST time, you should use

[root@testbed etc]# ln -sf /usr/share/zoneinfo/EST localtime