[mdlug] Clocks

[Wojtak, Greg]

There was a nice article on time drift in VMware on the VMware forums.  On 32-bit RHEL5, I had to add divider=10 clock=acpi_pm to the kernel line in grub and then change ntp's configuration to still sync even if the time is off by "a lot" (I can't remember what ntp's threshold is for bailing if the clock has drifted too far).  On 64-bit systems, I added the divider=10 notsc kernel options and modified ntp's config similarly.

-----Original Message-----
From: mdlug-bounces at mdlug.org [mailto:mdlug-bounces at mdlug.org] On Behalf Of Joe Doehler
Sent: Friday, December 18, 2009 9:35 AM
To: MDLUG's Main discussion list
Subject: Re: [mdlug] Clocks

Carl T. Miller wrote:
> Joe Doehler wrote:
>...
>
>> That was it! I had to change the clock source. I edited grub.conf to
>> make the change stick across reboots. Thanks.
>>
>> All that's left for me to is to tell the system to stop messing with the
>> hardware clock during shutdowns, so that ntpd can do its job properly.
> 
> Joe, this is the first I've heard of this.  What clock
> source were you using before and what did you change it to?
>...

There are three clock sources available on my system, called "pit", 
"jiffies" and "tsc". I found them following Ron's post. The installation 
program selected "pit", that seems to be the preferred one when using 
"VMware". I changed it to "tsc", and the system clock is now tracking 
the hardware clock. "jiffies" had the same problem. I have no idea what 
the difference is between them. I expect that ntps will now be able to 
handle hardware clock drifts.

Joe.

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