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

Betka, Corey betka at illinois.edu
Tue Sep 15 10:45:33 CDT 2009


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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