NTP

SERVER

Install NTP Server

               # yum install ntp

 

Setup Restrict values in ntp.conf

# vi /etc/ntp.conf

# Permit time synchronization with our time source, but do not

# Permit the source to query or modify the service on this system.

restrict default kod nomodify notrap nopeer noquery

restrict -6 default kod nomodify notrap nopeer noquery

 

Allow Only Specific Clients

# vi /etc/ntp.conf

restrict 172.16.0.0 mask 255.255.0.0 nomodify notrap

If the localhost needs to have the full access to query or modify, add the following line to /etc/ntp.conf

restrict 127.0.0.1

 

Add Local Clock as Backup

# vi /etc/ntp.conf

server 127.127.1.0 # local clock

fudge 127.127.1.0 stratum 10

 

Setup NTP Log Parameters

Specify the drift file and the log file location in your ntp.conf file

# vi /etc/ntp.conf

driftfile /var/lib/ntp/ntp.drift

logfile /var/log/ntp.log

 

Start the NTP Server

# service ntpd start

CLIENT

Modify ntp.conf on NTP Client

To synchronize the time of your local Linux client machine with NTP server, edit the /etc/ntp.conf file on the client side. Here is an example of how the sample entries look like. In the following example, you are specifying multiple servers to act as time server, which is helpful when one of the timeservers fails.

server 0.rhel.pool.ntp.org iburst

server 1.rhel.pool.ntp.org iburst

server 2.rhel.pool.ntp.org iburst

server 3.rhel.pool.ntp.org iburst

 

iburst: After every poll, a burst of eight packets is sent instead of one. When the server is not responding, packets are sent 16s interval. When the server responds, packets are sent every 2s.

 

Edit your ntp.conf to reflect appropriate entries for your own NTP server.

server 172.16.1.98 prefer

 

prefer: If this option is specified that server is preferred over other servers. A response from the preferred server will be discarded if it differs significantly different from other server’s responses.

 

Start the NTP Daemon

               # /etc/init.d/ntp start

 

Check the NTP Status

               # ntpq –p

 

Set Local Date and Time

               # ntpdate –u 172.16.1.98

               # ntpdc –c sysinfo