CentOS VM, NTP synchronization problems

Spirit asked:

We have three CentOS 5.9 VMs on an ESX3.5 host.

Because of the nature of the services we provide it is required that the NTP time is synchronized and the time is correct on all three of them.

However one of them constantly drifts back each day for about 66 sec.
So far none of us seems to understand as why is this happening.

We included the possibility that the VM may be somehow pulling the time from the host, however all of the three VMs have identical configuration settings and they did not have VMware tools installed.

Although I realize that this is probably a question of an internal matter and not to ask for on a forum, I would appreciate if anyone of you knows some CentOS NTP diagnostic routines that will help me to diagnose the problem and find a reliable solution.

I thank you for the assistance.

My answer:

If the clock drifts more than 500ppm in either direction, ntpd considers it insane and stops updating it. You will see a single log message when this happens (if you go looking for it). In this case you will need to use an alternate ntp client, such as chrony, which can be configured to continue to work in this scenario.

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