[ntp:questions] Re: NTP and Cron

Steven Hajducko Steven.Hajducko at DigitalInsight.com
Tue Nov 30 17:50:54 UTC 2004

>What you are are describing is not supposed to happen!  I find it 
>difficult to believe that a properly working ntp setup would allow the 
>time to get  out of synch by 14  seconds.  If it did, somehow, get that 
>far off it would step but the step you cite is in the positive 
>direction; it is setting the clock ahead, not back, and cron should not 
>see the same time  twice.

Well, good to know that it's a positive step, which means that this probably
wasn't the problem.

> Please provide some more details.  "cron jobs" suggests some Unix or 
> Linux variant but which one?   Which version of the NTP software are you 
> running?   On the chance that NTP is not properly configured, would you 
> consider posting your ntp.conf file?  What options are you specifying 
> when you start ntpd?

It's AIX 5.2, ML 4.  NTP v. = 3.4y ( This is from the logs, not sure if
that's correct, didn't install it ).
The NTP.conf is minimal -

driftfile /etc/ntp.drift
tracefile /etc/ntp.trace

In AIX, we start it as a subservice with no arguments specificed on the
commandline. ie ( startsrc -s xntpd ).

> Finally, assuming that ntp stepping the clock in either direction caused 
> the problem, I fail to see how a "monitoring script"  could prevent a 
> recurrence!  You might be able to detect a large clock step but you 
> would probably be too late to prevent a second instance of a job from 
> starting.

It wasn't meant to prevent.  It was meant to warn when it happened again.
However, I would rather learn how to prevent this problem then trying to
figure out a way to figure out when cron is firing off duplicate jobs in an
inappropriate time span.  ( Something that sounds a lot harder than trying
to get NTP configured correctly! :) )

> I believe the most effective prevention would be to locate the error 
> that caused the clock step and prevent a recurrence of that!

Totally agreed.  I'd just like to figure out if it was possible and if it
was, what we could do to prevent it. :)  

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