What is NTP , Configure private NTP server in Redhat Linux

Configuring NTP Server in REDHAT Linux

Before doing the configuration , we discuss some of the basic concepts about the NTP server.

What is NTP

NTP stands for Network Time Protocol, and it is an Internet protocol used to synchronize the clocks of computers to some time reference ,the time reference can be a computer or router device.

NTP uses Coordinated Universal Time (UTC) to synchronize computer clock times to a millisecond, and sometimes to a fraction of a millisecond. UTC time is obtained using several different methods, including radio and satellite systems. Specialized receivers are available for high-level services such as the Global Positioning System (GPS) and the governments of some nations. Computers and devices are designed to get the time from those servers or devices which are getting time information directly from radio and satellite systems.

NTP uses a hierarchical, semi-layered system of time sources. Each level of this hierarchy is termed a “stratum” and is assigned a number starting with zero at the top. A server synchronized to a stratum n server will be running at stratum n+1. The number represents the distance from the reference clock and is used to prevent cyclical dependencies in the hierarchy.


Accurate time across a network is important for many reasons; even small fractions of a second can cause problems. For example, distributed procedures depend on coordinated times to ensure that proper sequences are followed. Security mechanisms depend on coordinated times across the network. File system updates carried out by a number of computers also depend on synchronized clock times. Air traffic control systems provide a graphic illustration of the need for coordinated times, since flight paths require very precise timing (imagine the situation if air traffic controller computer clock times were not synchronized).

How to Configure NTP in REDHAT Linux

Configure NTP server :

1) Install the ntp package

rpm -ivh ntp-4.2.2p1-9.el5_3.2.x86_64.rpm


yum install ntp

2) Configure NTP Server

edit the /etc/ntp.cof

paste below lines into the file.

# Hosts on local network are less restricted.
restrict mask nomodify notrap

server prefer
fudge stratum 10

driftfile /var/lib/ntp/drift


NOTE : If you have your own NTP server use that server ipaddress instead of “server prefer” mentioned in the above file.

3) Configure the firewall

iptables -I INPUT -p udp –dport 123 -j ACCEPT

iptables -L

service iptables save

4) restart the service

service ntpd restart

after five minutes you can see output like below.

execute the “ntpq -p” command , you can see below output

Configure NTP Client

1) install ntp package as done for server

add below lines to the ntp.conf of client.

[root@node2 etc]# cat ntp.conf
# Point to our network’s master time server

restrict default ignore
restrict mask nomodify notrap noquery

driftfile /var/lib/ntp/drift

2)restart the ntp service

service ntpd restart

3) execute the “ntpq -p” , you can see the below output after 5 mins.

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