Set up NTP Server on Linux Server

This article describes the steps how to set up a NTP Server on your Local Network on RedHat, CentOS & Oracle Linux.

Table of contents:

– Network Time Protocol :

– Set UP NTP Server configuration:

– Set UP NTP Client configuration:

 1. Network Time Protocol:

Network Time Protocol (NTP) is a networking protocol for clock  synchronization between computer systems over packet-switched, variable-latency data networks. NTP is intended to synchronize all participating computers to within a few milliseconds of Coordinated Universal Time (UTC), for more info.

Setting up NTP is by installing the ntp package which contains utilities and daemons.

The ntp package includes ntpd (a daemon which continuously adjusts system time) and ntpdate (a program for retrieving the date and time from remote machines via a network).

 

 

 

To install the NTP package (on both NTP Client & Server side):

# yum install ntp
# chkconfig ntpd on

Note: Installing packages with YUM using DVD image.

Verify the NTPD Sysconfig configuration:

# cat /etc/sysconfig/ntpd
OPTIONS="-x -u ntp:ntp -p /var/run/ntpd.pid"

 2. Set UP Local  NTP Server:

Step 1: Add your Local Network.

My local network is 172.16.1.0/24, then adjust the network within the configuration file of the ntp server.

# vi /etc/ntp.conf
........
restrict  172.16.1.0 mask 255.255.255.0 nomodify notrap
......

Step2: Setting the Pool.ntp.org

Note: The NTP server is also a NTP Client of the pool.ntp.org, which is a big virtual cluster of timeservers providing reliable easy to use NTP service for millions of clients.

# vi /etc/ntp.conf
........
# Use public servers from the pool.ntp.org project.
server 0.rhel.pool.ntp.org
server 1.rhel.pool.ntp.org
server 2.rhel.pool.ntp.org
........

Step 3 :To Synchronize our NTP Server with the pool.ntp.org, we can use the tool ntpdate directly or while the Linux server start will automatically synchronize his date if there are an internet connection:

# ntpdate -u 0.rhel.pool.ntp.org
31 Aug 10:32:47 ntpdate[3391]: adjust time server 41.231.53.4 offset -0.000237 sec

 

 

Step 4: Update your Firewall:

Update your firewall, the port number of the NTP Server is 123 while using the UDP protocol.

# iptables -A INPUT -s 172.16.1.0/24 -m state --state NEW -p udp --dport 123 -j ACCEPT 
# iptables-save

 2. Set UP NTP Client:

Step 1: Editing the file /etc/ntp.conf to add the NTP Server IP address.

# vi /etc/ntp.conf
........
# Use public servers from the pool.ntp.org project.
server 172.16.1.123
........

Step 2: To synchronize immediatelly, we can use the tool ntpdate:

# ntpdate -u 172.16.1.123
31 Aug 10:38:54 ntpdate[2778]: adjust time server 172.16.1.123 offset -0.001602 sec

 

 

Note: By enabling the service ntpd, then the Linux Server will update the date automatically while starting.

Conclusion:

This article describes the steps how to create a local NTP Server and to configure NTP clients.