[CentOS] NTP and hardware clock

Stephen John Smoogen smooge at gmail.com
Wed Oct 11 18:41:10 UTC 2006

On 10/11/06, Dag Wieers <dag at wieers.com> wrote:
> On Wed, 11 Oct 2006, mike.redan at bell.ca wrote:
> >
> > > The whole point of ntpdate is to synchronize the local clock with
> > > another source (ie. not the local clock).
> > >
> > > And I guess the main reason why they do not start ntpd if ntpdate
> > > fails, is because they have to protect other ntp clients from being
> > > poisoned by a wrong system clock upstream (because its source is
> > > unavailable).
> >
> > Hrm. What does your initscript look like for ntpd? Ie which version? I
> > just had a look around at some RHEL3.x and 4.x (as well as some CentOS
> > ones) and none of them will refuse to start ntpd if the ntpdate run
> > fails. The only thing they do when ntpdate fails is add the "-g" option,
> > which will let ntpd jump the clock more than 1000s. But no matter what,
> > ntpd will start.
> You're correct. Then I have no idea why ntpd was not running.

/me puts on his ntpd hat.

ntpd will not start running if it finds it can't make a gradual change
to the clock to bring it into sync. This occurs when the clock is over
1000s or the TOY chip is not responding in a way that the ntpd knows
how. [If hwclock --systohc says it sets the clock but you see it
doesnt.. then it can be a hardware problem of many types.]

The most common reason I found ntpd not running is that it found its
time all of a sudden over 1000s for some reason it didnt know about
(changing timezone on the box or bad hz rate from hardware.)

Stephen J Smoogen. -- CSIRT/Linux System Administrator
How far that little candle throws his beams! So shines a good deed
in a naughty world. = Shakespeare. "The Merchant of Venice"

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