[CentOS] clock sync/drift

Wed Jan 23 10:06:35 UTC 2013
Leon Fauster <leonfauster at googlemail.com>

Am 23.01.2013 um 06:21 schrieb Ron Loftin <reloftin at twcny.rr.com>:
> On Tue, 2013-01-22 at 21:16 -0600, Matt Garman wrote:
>> Hi,
>> We have a little over 100 servers, almost all running CentOS 5.7.
>> Virtually all are Dell servers, generally a mix of 1950s, R610s, and
>> R410s.
>> We use NTP and/or PTP to sync their clocks.  One phenomenon we've
>> noticed is that (1) on reboot, the clocks are all greatly out of sync,
>> and (2) if the PTP or NTP process is stopped, the clocks start
>> drifting very quickly.
>> If it was isolated to one or two servers, I'd dismiss the issue.  I
>> also had this problem under CentOS 4.
>> I suspect something is mis-configured, because I can't imagine the
>> hardware clock on ALL these servers is *that* bad.
> Well -- in my experience ( 15+ years with RH variants of Linux, and ~25
> with various Unix flavors ) they CAN be that bad -- especially with some
> of the "economy" chipsets used with the Intel architecture.  It gets
> worse when you have a CMOS battery that's getting old and weak.  The
> clock may default back to its initial value, or it might just run slow.
> Some folks might consider this a "brute force" approach, but I keep it
> simple and just reset the hardware clock once a week via cron.  I prefer
> to do it in the wee hours, shortly before the weekly cron jobs run on
> Sunday morning.  Put something like this in root's crontab.
> 3 3 * * 0       /sbin/hwclock --systohc

this is already done in /etc/rc.d/init.d/halt on halt/reboot.