configuration – How do I change my timezone to UTC/GMT?

In the old Un*x style (SunOS, HPUX…), you can do:

ln -fs /usr/share/zoneinfo/UTC /etc/localtime

Check the contents of /usr/share/zoneinfo to get the timezone you want/need.

For instance, Irish Summer Time (IST) can be defined as

-rw-r--r-- 1 root root 3661 Mar 13 22:18 /usr/share/zoneinfo/posix/Eire

or

lrwxrwxrwx 1 root root 13 Mar 13 22:18 /usr/share/zoneinfo/Europe/Dublin -> ../posix/Eire

However, the most important is to use a proper clock reference and a ntp daemon (openntpd for instance), as timezone is only used for displaying/converting the time to strings, not to store it (whatever the timezone, difference to 01/01/1970 is everywhere the same on Earth).