ntp : ntpd server which continuously adjusts system time and utilities used to query and configure the ntpd daemon.
ntpdate : Utility to set the date and time via NTP.
ntp-doc : NTP documentation
Setup NTPD on CentOS Linux
# yum install ntp ntpdate ntp-doc
Turn on service, enter:
# chkconfig ntpd on
Synchronize the system clock with 0.pool.ntp.org server (use this command only once or as required):
# ntpdate pool.ntp.org
Start the NTP server. The following will continuously adjusts system time from upstream NTP server. No need to run ntpdate:
# /etc/init.d/ntpd start
web reference : https://www.cyberciti.biz/faq/howto-install-ntp-to-synchronize-server-clock/