[ntp:questions] NTP and Cron

Steven Hajducko Steven.Hajducko at DigitalInsight.com
Mon Nov 29 20:57:21 UTC 2004

Is it possible for NTP to reset the time back enough that cron will fire off
jobs twice?

I realize it's poor programming in whatever jobs we have running that they
don't check if they're already running, but that is out of my hands.  The
issue that was given to me was to write a monitoring script around it
happening again.  I'd instead like to make sure that NTP can't do that.  Do
you have to specify a threshold for time increments and if so, is it
possible to set the time increments to be under 1 second ( or is this the
default already? )

In our log, we have the following:

Nov 23 08:55:25 xeon xntpd[10464]: time reset (step) 14.427314 s

And afterwards, the log goes on to show one of the jobs firing off, again.
I'm not exactly sure this IS the issue, as I don't see how it could have set
off another cronjob, being that 14 second step would have simply gone to
8:55:11, or if that timestamp is after the step, then 8:55:39 and since cron
only goes by a minimum of minutes, well...

But I'd like to clear up the issue so I can present it to them.  So is it
possible for NTP to reset the time in a big enough increment that it could
make cron fire off a job twice?  And if so, are there ways to prevent that?


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