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ESXi 4.1 NTP client not syncing time

Posted on 2011-09-13
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Last Modified: 2012-05-12
I installed ESXi v4.1 on several servers and configured NTP to synchronize the time using my internal NTP server which runs on my core switch.  In order to get NTP to sync, I had to restart the management agent on each host.  So my question is why is this step necessary, shouldn't that happen automatically when the host is rebooted?

I rebooted several times, but time would not sync until I manually went to the ESXi console and restarted the management agents.  This has me wondering if NTP will continue to sync or if it will break again after the next reboot.

Since these servers will be deployed out to satellite offices, there will not be IT staff around to check up on them periodically, and I would like to ensure that their NTP configuration continues to work, and I'm not sure that will be the case if you have to restart the management agents manually after booting the host to get it to sync.
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Question by:FWeston
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by:Andrew Hancock (VMware vExpert / EE MVE)
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NTP Time Sync with ESXi 4.1 syncs at random time intervals, what makes you think that time syncing is not occuring?

Have you setup NTP correctly to start at boot? using the vSphere GUI client?
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by:FWeston
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The fact that I set up NTP, restarted the NTP service, came back 30 minutes later and the time was still incorrect leads me to believe that NTP was not syncing.  Then I rebooted, waited another 30 minutes, same result.  Then I restarted the management agents and it synced within 5 minutes.

My point is that shouldn't the management agents be restarted every time the host reboots?  If that's the case, then what's different about me restarting the host and NTP not syncing vs manually restarting the management agents after which the NTP sync did work?

I guess after the initial sync, I don't care when it syncs, but I just want to make sure that once I have gotten it to sync once, it should be good to go forever?
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by:Andrew Hancock (VMware vExpert / EE MVE)
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Is your NTP source accurate and correct?

If you start or restart the NTP service from the vSphere GUI Client, it should Sync immediately, if the time source is correct.

You should not have to restart network management agents, to force a sync.

What is your NTP source?
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by:Andrew Hancock (VMware vExpert / EE MVE)
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If you do not have a Stable NTP time source, ESX NTP will not sync and it will ignore the time source.

we've certainly not experienced any issues with ESX NTP sync, and we have many ESX installations in our offices, and we manage many client installations at our datacentre, and have many clients that manage their own.

We have seen if NTP source is not stable, ESX will not sync, and ignore NTP, we are also aware that VMware admins, are unhappy, that there is no regular interval, e.g. ever 600 seconds that it syncs, and there was no last sync time provided for diagnostics.

But usuaully, Stopping and Starting should Sync immediately, providing accurate and stable time source.
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by:BloodRed
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Check out this ESXi NTP guide:

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1003063

Also, try setting your hardware clock to be consistent with the system clock which is updated via the NTP daemon with the '/sbin/hwclock --systohc' command.

What settings does your NTP source use? ESX's NTP client can be picky about the time dispersion setting of it's NTP source, check out this KB for more details.

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=103583
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by:FWeston
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My NTP source is my core Cisco switch, which is both accurate and reliable.  It seems to be staying synced now, but I'm confused as to why I had to restart the management agents to get it to sync the first time.
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Andrew Hancock (VMware vExpert / EE MVE) earned 500 total points
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The only thing that springs to mind, is that the NTP service was not running or hung.

Meinberg NTP software has helped us many times, install it on a PC or Server, point to your internal NTP host, and it will create graphs, and warn if down or accuracy.

http://www.meinberg.de/english/sw/ntp.htm

We have found in the past when using Cisco routers, if the Upstream NTP source was down, the Cisco routers did not output correct time, and was ignored by ESX servers, hence why have now moved over to our own NTP servers, which sync from multiple sources, or Symmetricom NTP appliances

http://www.symmetricom.com/products/ntp-servers/ntp-network-appliances/

If using a GPS based device, you can be guaranteed of a correct time source, 24x7, 365 days a year, rather than relying on internet based time sources.
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