In Main Server:
# vi /etc/ntp.conf
select a server.
eg: 0.centos.pool.ntp.org
# ntpdate servername
eg: ntpdate 0.centos.pool.ntp.org
In Main Server:
# vi /etc/ntp.conf
select a server.
eg: 0.centos.pool.ntp.org
# ntpdate servername
eg: ntpdate 0.centos.pool.ntp.org