[CentOS] clock sync/drift
reloftin at twcny.rr.com
Wed Jan 23 05:21:42 UTC 2013
On Tue, 2013-01-22 at 21:16 -0600, Matt Garman wrote:
> 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
> 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
For the gory details, refer to the man page for "hwclock" and it will
> Anyone else dealt with anything similar?
> CentOS mailing list
> CentOS at centos.org
Ron Loftin reloftin at twcny.rr.com
"God, root, what is difference ?" Piter from UserFriendly
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