[CentOS] CentOs 5.6 and Time Sync

Brandon Ooi

brandono at gmail.com
Mon May 9 23:53:47 UTC 2011


On Mon, Apr 25, 2011 at 12:47 PM, Denniston, Todd A CIV NAVSURFWARCENDIV
Crane <todd.denniston at navy.mil> wrote:

>
>
> > -----Original Message-----
> > From: centos-bounces at centos.org [mailto:centos-bounces at centos.org] On
> > Behalf Of Mailing List
> > Sent: Monday, April 25, 2011 13:57
> > To: CentOS mailing list
> > Subject: Re: [CentOS] CentOs 5.6 and Time Sync
> >
> >
> >
> >      List,
> >
> >      I was not able to resolve my issue with the time on this machine.
> > I
> > went ahead and rolled the update back to 5.5 and disabled the update
> to
> > 5.6.
> >
> >     What I would like to know is if CentOS 6 might be ok when it rolls
> > out, or am I just going to have to keep with 5.5 till EOL?
> >
> >    Thanks to all with there help.
> >
>
> 1) I hope you are only talking about having rolled back to the last
> working for you kernel from 5.5, not the whole distribution.
>
> 2) If I was in your position and had time, my method would be[1]
>  a) get the srpm for the last known working kernel (2.6.18-194.32 ???)
>  b) get the srpm for the first known not working kernel (2.6.18-238 ???)
>  c) expand each of the above srpms into their own rpm build tree
>    i.e., rpmdev-setuptree;rpm -i kern1; mv rpmbuild rpmbuild.kern1;
>          rpmdev-setuptree;rpm -i kern2; mv rpmbuild rpmbuild.kern2
>  d) start looking at the differences in the patches applied in kern1 vs.
> those in kern2, i.e., read/diff the kernel.spec files
>   see if there were any new ones that seemed likely to be causing the
> problem...
>   RTFS if necessary to make better guesses.
>   Rebuild kernel 2 with patches taken out/modified based on my
> investigations and test them and see if I guessed right.
>   If no luck, think about opening an TUV bug with lots of the info you
> have sent here, they may be interested even if you don't have a
> subscription.
>
> [1] Been there, done that:
> http://www.gossamer-threads.com/lists/drbd/users/9616
>
>
At first I figured this was misconfigured NTP but I actually see this
happening on one of my machines as well. Nothing interesting about it in
particular but I verified that rolling back to the previous kernel
(2.6.18-194.32.1.el5) solves the problem entirely. This happens when NTP is
enabled or disabled. I get the following error messages in dmesg which are
possibly related.

time.c: can't update CMOS clock from 59 to 0
time.c: can't update CMOS clock from 59 to 0
time.c: can't update CMOS clock from 59 to 0
time.c: can't update CMOS clock from 59 to 0

The time drift is significantly higher than would be expected as normal.
Because rolling back the kernel completely solves this issue, this must be a
bug.

[root at nexus4 ~]# date; ntpdate -u pool.ntp.org
Mon May  9 16:51:03 PDT 2011
 9 May 16:50:21 ntpdate[22117]: step time server 207.182.243.123 offset
-42.418572 sec

[root at nexus4 ~]# date; ntpdate -u pool.ntp.org
Mon May  9 16:50:33 PDT 2011
 9 May 16:50:35 ntpdate[22127]: step time server 207.182.243.123 offset
-0.692146 sec

Brandon
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