Install and configure NTP on CentOS 5.3

1. Install NTP (Network Time Protocol):
   yum -y install ntp
   
   
2. Edit the NTP config file:
   vi /etc/ntp.conf
   
   
3. At line 18, find "server 2.centos.pool.ntp.org" and under, add:
   server time.nrc.ca
   server time.chu.nrc.ca
   server tock.utoronto.ca
   server tick.utoronto.ca
   
   
4. Ajust the other NTP config file by editing:
   vi /etc/sysconfig/ntpd
   
   
5. At that file's second line:
   OPTIONS="-u ntp:ntp -p /var/run/ntpd.pid"
   
   
6. Modify this line to add the option -x that will force a NTP synch at boot time:
   OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"
   
   
7. Restart NTPD service:
   service ntpd start
   
   
8. Ajust system to automaticaly start the service at boot:
   chkconfig ntpd on
   
   Reference link