How to configure NTP servers in Linux?

petulia3478

To configure two ntp servers:

On each of the two ntp servers, add "server 127.127.1.0 # local clock" to the file /etc/ntp.conf:

# vi /etc/ntp.conf

server 127.127.1.0 # local clock

Set the date/time on both servers (replace xxxxxx with the appropriate value):

# date xxxxxx

Switch ntp ON for init levels 3 & 5

# chkconfig --level 35 ntpd on

Manually start ntp:

# service ntpd start

On all clients:
Create a cron job to make the clients synchronise with the ntp servers every hour:

# crontab -e

00 0-23 * * * /usr/sbin/ntpupdate <ip_address1> <ip_address2>

Where <ip_address1> <ip_address2> are the IP addresses of the two ntp servers you have just configured.

It is also possible to use the hostname of the two ntp servers as opposed to their IP addresses as above, in case IP addresses change. For example:

# crontab -e

00 0-23 * * * /usr/sbin/ntpupdate <hostname1> <hostname2>

To check status of ntp:

# ntpq -p

Many other ntpq options are available:

# ntpq
ntpq> help
Commands available:
addvars        associations   authenticate   cl             clearvars
clocklist      clockvar       cooked         cv             debug
delay          exit           help           host           hostnames
keyid          keytype        lassociations  lopeers        lpassociations
lpeers         mreadlist      mreadvar       mrl            mrv
ntpversion     opeers         passociations  passwd         peers
poll           pstatus        quit           raw            readlist
readvar        rl             rmvars         rv             showv


# ntpq -p -n
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.1.0     LOCAL         10 l    3   64  377    0.000    0.000   0.001