Vmware ESXi (3.5) and RHEL (5.1) : Timekeeping Woes

Zach White zach at box.net
Tue Sep 15 10:32:45 CDT 2009


To summarize that document for the lazy: Don't use ntpd inside a VM.

There are very real issues with how time is kept on a computer that  
mean that your VM will never keep time as accurately as a physical  
server. The issue is further complicated by the manor in which ntpd  
keeps your computer's clock accurate. VMware's solution to this  
problem is a once a minute time syncing with the host computer and  
providing the document Jens references, which is actually very  
interesting if you want to understand how a computer perceives time.

In a previous job I ran into this using VMware server. For some reason  
the built-in time synchronization wasn't working properly, so I  
disabled it and used the following cron job:

*/5 * * * *     ntpdate -s physical.machine.running.ntpd

However, on our ESXi hosts we had no problems using "Synchronize guest  
time with host" so we left it turned on and did not use the above cron  
job. YMMV.

-Zach

On Sep 15, 2009, at 5:14 AM, Mueller, Jens wrote:

> Hi Brian,
>
> There is a kb from vmware due to timekeeping problems in linux  
> virtual machines
>
> http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006427
>
> Regards
>
> Jens
>
> From: linux-poweredge-bounces at lists.us.dell.com [mailto:linux- 
> poweredge-bounces at lists.us.dell.com] On Behalf Of Brian O'Mahony
> Sent: Tuesday, September 15, 2009 13:45
> To: linux-poweredge at lists.us.dell.com
> Subject: Vmware ESXi (3.5) and RHEL (5.1) : Timekeeping Woes
>
> I may have posted this here previously, and if not I know I spoke to  
> Dell support, whom advised me to make sure that the “Synchronize  
> guest time with host” was turned off.
>
> Basically I have a RHEL5.1 server. It has the ntpd service running.  
> This seems to stop every now and again. It took me quite some time  
> to organize downtime on this VM, so I only got to turn off the  
> option in setting last week.
>
> Here is the log from messages:
>
> messages:Sep 13 10:28:07 curzilla ntpd[2593]: synchronized to LOCAL 
> (0), stratum 10
> messages:Sep 13 11:35:50 curzilla ntpd[2593]: synchronized to  
> 172.16.164.100, stratum 4
> messages:Sep 13 15:18:10 curzilla ntpd[2593]: synchronized to LOCAL 
> (0), stratum 10
> messages:Sep 13 19:33:29 curzilla ntpd[2593]: synchronized to  
> 172.16.164.100, stratum 4
> messages:Sep 14 08:04:52 curzilla ntpd[2593]: synchronized to LOCAL 
> (0), stratum 10
> messages:Sep 14 09:30:14 curzilla ntpd[2593]: synchronized to  
> 172.16.164.100, stratum 4
> messages:Sep 14 22:01:36 curzilla ntpd[2593]: synchronized to LOCAL 
> (0), stratum 10
> messages:Sep 15 01:10:27 curzilla ntpd[2593]: synchronized to  
> 172.16.164.100, stratum 4
> messages:Sep 15 01:26:28 curzilla ntpd[2593]: time correction of  
> 2232 seconds exceeds sanity limit (1000); set clock manually to the
>  correct UTC time.
>
>
>
> Anyone have any ideas/suggestions?
>
> B
>
>
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