（１）まず最初にntp.confを修正します

#vi /etc/ntp.conf

ファイルを開いたら

# # Undisciplined Local Clock. This is a fake driver intended for backup # and when no outside source of synchronized time is available. The # default stratum is usually 3, but in this case we elect to use stratum # 0. Since the server line does not have the prefer keyword, this driver # is never used for synchronization, unless no other other # synchronization source is available. In case the local host is # controlled by some external source, such as an external oscillator or # another protocol, the prefer keyword would cause the local host to # disregard all other synchronization sources, unless the kernel # modifications are in use and declare an unsynchronized condition. # #server 127.127.1.0 # local clock fudge 127.127.1.0 stratum 10 # # Drift file. Put this in a directory which the daemon can write to. # No symbolic links allowed, either, since the daemon updates the file # by creating a temporary in the same directory and then rename()'ing # it to the file. # driftfile /etc/ntp/drift multicastclient # listen on default 224.0.1.1 broadcastdelay 0.008 # # Keys file. If you want to diddle your server at run time, make a # keys file (mode 600 for sure) and define the key number to be # used for making requests. # # PLEASE DO NOT USE THE DEFAULT VALUES HERE. Pick your own, or remote # systems might be able to reset your clock at will. Note also that # ntpd is started with a -A flag, disabling authentication, that # will have to be removed as well. # #keys /etc/ntp/keys

このファイルの最後に各プロバイダでも公開されているntpサーバーまたは、
国内公開 ntp サイト一覧
などを参考にして

server ***.***.***.***

の行を追加します。(***はntpサーバーアドレス)

（２）ntp.confを修正して保存したら、ntpサーバーと同期をとるために
ntpdateコマンドで時計を合わせ直します。

（３）NTPDを起動します。

#/etc/rc.d/init.d/ntpd start

（４）動作確認

#/usr/sbin/ntpq -p 　remote　　refid　　　　　　st t when　poll 　reach　delay　offset　 jitter ============================================================================== *ntp2.jst.mfeed. 210.173.160.86　　2 u 　3　64　1　39.731　21.946　0.002

しばらくして*が表示されたら同期完了です。(ローカルの時計との誤差が+-１分ぐらいでないと同期できません。）

（５）再起動後自動起動するように設定します。

#/sbin/chkconfig ntpd on