To check if ntpd is configured:
$chkconfig --list ntpd
ntpd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
Install and configure ntpd if not configured:
#yum install ntp ntpdate ntp-doc
#chkconfig ntpd on
Initial time synchronization:
#ntpdate <ntp-srv-IP-address>
Configure ntpd:
Into /etc/ntpd.conf add NTP server and comment out default servers if necessary:
server <...>
Start ntpd:
#/etc/init.d/ntpd start
or
#service ntpd start
Check if ntpd is working:
$ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
+clock.util.phx2 .CDMA. 1 u 111 128 377 175.495 3.076 2.250
*clock02.util.ph .CDMA. 1 u 69 128 377 175.357 7.641 3.671
ms21.snowflakeh .STEP. 16 u - 1024 0 0.000 0.000 0.000
The command lists connected time servers and displays information indicating when they were last polled and the stability of the replies. The column headings are as follows:
-
remote and refid: remote NTP server, and its NTP server
-
st: stratum of server
-
t: type of server (local, unicast, multicast, or broadcast)
-
poll: how frequently to query server (in seconds)
-
when: how long since last poll (in seconds)
-
reach: octal bitmask of success or failure of last 8 queries (left-shifted); 377 = 11111111 = all recent queries were successful; 257 = 10101111 = 4 most recent were successful, 5 and 7 failed
-
delay: network round trip time (in milliseconds)
-
offset: difference between local clock and remote clock (in milliseconds)
-
jitter: difference of successive time values from server (high jitter could be due to an unstable clock or, more likely, poor network performance)
To obtain summary:
$ntpstat
synchronised to NTP server (10.5.26.10) at stratum 2
time correct to within 52 ms
polling server every 1024 s
!! If there is a big gap between local and NTP time we need to stop ntpd daemon, perform synchronization with ntpdate and start ntpd again.
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