Prerequisites Step 1: Endure you are in the correct time zone

# timedatectl
      Local time: Wed 2018-09-12 13:48:31 +08
  Universal time: Wed 2018-09-12 05:48:31 UTC
        RTC time: Wed 2018-09-12 05:48:31
       Time zone: Asia/Singapore (+08, +0800)
     NTP enabled: yes
NTP synchronized: yes
 RTC in local TZ: no
      DST active: n/a

Prerequisites Step 2: List Time Zone

# timedatectl list-timezones
.....
Asia/Singapore
.....

Prerequisites Step 3: Set Time Zone

# timedatectl set-timezone Asia/Singapore

 

Step 1: Yum Install

NTP can be installed from the CentOS repositories with yum

# yum install ntp

Step 2: Edit the Public Time Servers

Once you have installed ntp package, go to official NTP Public Pool Time Servers . For Singapore, you can use this specific pool zone, add the following to your ntp.conf file:

server 0.sg.pool.ntp.org iburst
server 1.sg.pool.ntp.org iburst
server 2.sg.pool.ntp.org iburst
server 3.sg.pool.ntp.org iburst

Step 3: Allow the clients from the network to sync with this server

Restrict which clients from which network is allowed to query and sync time

restrict 192.168.5.0 netmask 255.255.224.0 nomodify notrap

Step 4: Record all NTP server issues into one dedicated log file. Edit /etc/ntp.conf

logfile /var/log/ntp.log

Step 5: Add Firewall Rule and Start Services

# firewall-cmd --add-service=ntp --permanent
# firewall-cmd --reload

# systemctl start ntpd
# systemctl enable ntpd
# systemctl status ntpd

Step 6: Verify Time Sync

# ntpq -p
# date -R

Or query or synchronize against a selected pool of time servers

# ntpdate -q 0.sg.pool.ntp.org

References:

1. Setting Up “NTP (Network Time Protocol) Server” in RHEL/CentOS 7 (by Tecmint.com)