Setting Up NTP (Network Time Protocol) Server in RHEL/CentOS 7

Network Time Protocol (NTP) is a networking protocol used to synchronize the clocks of computers over a network. Setting up an NTP server in RHEL/CentOS 7 allows you to provide accurate time synchronization to client devices across your network infrastructure.

Prerequisites

Before configuring the NTP server, ensure you have root privileges and network connectivity to external NTP sources. The server should also have proper DNS resolution configured for accessing public NTP servers.

Install NTP Package

First, install the NTP package using the YUM package manager. This provides the necessary software components to run an NTP server on your RHEL/CentOS 7 system.

sudo yum install ntp

Verify the installation by checking if the NTP daemon is available:

rpm -qa | grep ntp

Configure NTP Server

Edit the main NTP configuration file located at /etc/ntp.conf. This file contains server definitions, access controls, and other NTP-specific settings.

sudo nano /etc/ntp.conf

Add or modify the server entries to specify your preferred time sources. For example:

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

The iburst option sends a burst of packets for faster initial synchronization.

Configure Firewall

NTP uses UDP port 123 for communication. Open this port in the firewall to allow NTP traffic from client devices.

sudo firewall-cmd --add-port=123/udp --permanent
sudo firewall-cmd --reload

For systems using iptables instead of firewalld:

sudo iptables -A INPUT -p udp --dport 123 -j ACCEPT
sudo service iptables save

Start and Enable NTP Service

Start the NTP daemon and configure it to start automatically at boot time:

sudo systemctl start ntpd
sudo systemctl enable ntpd

Verify the service status:

sudo systemctl status ntpd

Verify NTP Synchronization

Check if your NTP server is properly synchronizing with upstream servers:

ntpq -p

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*0.centos.pool.n 192.168.1.1     2 u   64   64  377    1.234   -0.567   0.123
+1.centos.pool.n 10.0.0.1        2 u   32   64  377    2.345   +1.234   0.234

The asterisk (*) indicates the currently selected reference server, while plus (+) shows backup servers.

Client Configuration

To configure client machines to use your NTP server, modify their /etc/ntp.conf file:

server your_ntp_server_ip iburst

Replace your_ntp_server_ip with your NTP server's actual IP address.

Conclusion

Setting up an NTP server in RHEL/CentOS 7 involves installing the NTP package, configuring time sources, opening firewall ports, and enabling the service. Once configured, your NTP server will provide accurate time synchronization to client devices, ensuring consistent timekeeping across your network infrastructure.