The Network Time Protocol (NTP) enables the accurate dissemination of time and date information to synchronise the time clocks on networked computer systems.
In CentOS, it is effortless to install and configure the NTP client. Install your NTP client using the yum command:
NTP Server Configuration
1. Install the required ntp the package on the server.
# yum install ntp
2. Ensure the following entries are in ntp configuration file /etc/ntp.conf.
# cat /etc/ntp.conf restrict default kod nomodify notrap nopeer noquery restrict -6 default kod nomodify notrap nopeer noquery restrict 127.0.0.1 restrict -6 ::1 server 0.pool.ntp.org server 1.pool.ntp.org server 2.pool.ntp.org server 3.pool.ntp.org restrict 10.10.10.0 mask 255.255.255.0 nomodify notrap driftfile /var/lib/ntp/drift keys /etc/ntp/keys
As per the configuration file the NTP servers are only to the NTP clients in the subnet 10.10.10.0/24. You can get the public NTP servers specific to your region from pool.ntp.org.
In the /etc/ntp.conf the file you will have to mention the NTP server(s) in your environment.
3. Now you can start the ntpd service.
For RHEL 5,6:
# service ntpd start
For RHEL 7:
# systemctl start ntpd.service
NTP Client Configuration
1. For client NTP configuration, add the below configuration in the /etc/ntp.conf file.
# cat /etc/ntp.conf restrict default kod nomodify notrap nopeer noquery restrict -6 default kod nomodify notrap nopeer noquery restrict 127.0.0.1 restrict -6 ::1 server ntp.server.com driftfile /var/lib/ntp/drift keys /etc/ntp/keys
Here, ntp.server.com is the server you configured as NTP server in the example shown at the start of the post. There can be multiple NTP servers for redundancy purpose. Add a new line for each of the NTP servers in the /etc/ntp.conf file.
2. Start the ntpd service on the ntp client server.
For RHEL 5,6:
# service ntpd start
For RHEL 7:
# systemctl start ntpd.service
