Time setting in Linux, Unix

[Time server list in South Korea]
1. NTP Primary Time Server
    - time.kriss.re.kr
    - time2.kriss.re.kr
    - ntp.kornet.net
    - ntp.postech.ac.kr
    - time.bora.net

2. NTP Secondary Time Server
    - ntp.ewha.net
    - ticktock.ewha.net
    - time.bora.net

[rdate]
$ sudo rdate - s time-server-name

[ntpdate]
$ sudo ntpdate -b time-server-name

You should not repeat the time request in short time (seconds).
You can be added to black list and blocked.

[Time zone setting in Ubuntu]
$ sudo ln -sf /usr/share/zoneinfo/Asia/Seoul /etc/localtime
$ date
Mon Feb 13 16:13:21 KST 2012

"KST" means Korea time zone.