NTP Troubleshooting

Aruba Employee

PROBLEM :
The server time is off even though NTP is configured and enabled.

TROUBLESHOOTING STEPS :

Use the ntpdc -p command to check the current status of ntpd.

# ntpdc -p
remote local st poll reach delay offset disp
=======================================================================
=LOCAL(0) 127.0.0.1 10 64 377 0.00000 0.000000 0.03032
*mail.melancthon 10.162.110.36 2 64 377 0.07680 0.013330 0.06358
=64.73.32.134 10.162.110.36 2 64 377 0.07994 0.013961 0.06413

Each line is a different reference point. The one that begins with a '*' is the current reference point and the server that will be synced with. The offset column is in seconds. If one server shows an offset of -360.000, it means that server thinks your time is set 5 minutes too fast.

You want to confirm that one of the servers is selected as a reference point that is *not* the LOCAL server. Also, confirm that the offset from whatever reference server is selected shows an offset of near 0.

=== ADDITIONAL TROUBLESHOOTING ===
Modify the /etc/ntp.conf file manually and add the following line the end (if it doesn't already exist). This will print ntpd status to the log file location.

logfile /var/log/ntp.log

Additionally, iburst can be enabled for each NTP server. Edit the /etc/ntp.conf and add "iburst" to the end of each. This will send a burst a packets if the initial request failed. It prevents NTP from giving up on a valid NTP server and choosing a bad reference server such as LOCAL.

server 0.centos.pool.ntp.org iburst
server 1.centos.pool.ntp.org iburst
server 2.centos.pool.ntp.org iburst

For these additional steps modifying the configuration file, ntpd must be restarted.

# /etc/init.d/ntpd restart

=== RELATED LINKS ===
http://www.meinberg.de/english/info/ntp.htm#ntp_status - This site has a great description of understanding each column in the ntpdc -p command.
https://wiki.archlinux.org/index.php/Network_Time_Protocol_daemon#Configuring_connection_to_NTP_servers - This site details what each line of the ntp.conf does. Not everything from this link should be followed since it is not based off of CentOS.

Version history
Revision #:
1 of 1
Last update:
‎06-29-2014 10:03 AM
Updated by:
 
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