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

Zach White zach at box.net
Tue Sep 15 11:00:12 CDT 2009


Apparently VMware's advice has changed since I last worked with this  
stuff. I apologize to anyone I may have misled with outdated  
information.

-Zach

On Sep 15, 2009, at 8:45 AM, Betka, Corey wrote:

> Actually, VMware has changed their best practices for timekeeping in  
> a VM and has specific recommendations for various flavors, including  
> using NTP, setting certain kernel options and disabling timesync  
> from the VMware tools.
>
> In the early days, disabling NTPd was the way to go, but it’s not  
> anymore.
>
> http://kb.vmware.com/kb/1006427 (same article as below, just a  
> shorter link)
>
> Corey
>
> From: linux-poweredge-bounces at lists.us.dell.com [mailto:linux- 
> poweredge-bounces at lists.us.dell.com] On Behalf Of Zach White
> Sent: Tuesday, September 15, 2009 10:33 AM
> To: linux-poweredge at lists.us.dell.com
> Subject: Re: Vmware ESXi (3.5) and RHEL (5.1) : Timekeeping Woes
>
> 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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