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[Pyatcron-devel-list] Cron and the "*/45" entry
From: |
NICOLOVICI Xavier |
Subject: |
[Pyatcron-devel-list] Cron and the "*/45" entry |
Date: |
Thu, 20 Nov 2003 17:09:29 +0100 |
> > I tried the cron task, and set it up with my schedule
> looking like this:
> >
> > */45 * * * * /bin/mycommand
> >
> > I watched my email, and noticed that it is firing the task
> at the top of
> > every hour and at the 45th minute of every hour. It is NOT, running
> > every 45 minutes like I would expect it to.
> >
> > I'm starting to think that */n in the minutes column actually means:
> > 0-59 and step by n minutes. And if n = 45 then it would
> run at 0 and 45
> > minutes on every hour (assuming the hour field is *). And if n = 10
> > then it would run at 0,10,20,30,40,50. So before we just
> assume that
> > */45 means run every 45 minutes, and before we start crafting a GUI
> > based on this assumption, we may want to do a little more
> research into
> > it. Did anyone else try this little experiment?
> >
>
> I did a similar test (*/7) and it seems that you're right. It doesn't
> run every 7 minutes. It goes from min 56 to min 0 instead of min 3.
>
> We'll have to re-think about it I guess...
>
Hmm, not re-think, but get back to the first idea I guess, having list of
integers as parameters.
Explanation: I went through the way Cron works, and in fact, for each time/date
entry, it builds internally a list of "true" value. In other words, looking at
the minute fields for example, Cron builds internally a list of minute value
when the task is allowed to run.
The "*", "nn-mm" or the "X/nn" representations are made to be human readable,
but when Cron parse the crontab files, it builds list of values.
The "*" becomes "1,2,3,4,5,6,7,8,9,10,...56,57,58,59", "20-25" becomes
"20,21,22,23,24,25" and finally, "*/22" which means every minutes from 0 with
an increment step of 22 becomes "0,22,44"; This is really not "execute every 22
minutes" but "build a list of values from 0 to 59 with an increment step of 22
and use this list as true values for the minute field".
So, in conclusion, if everyone agrees, I would like to fall back to list of
integers for the get/set functions of the Scheduler. Then, the role of the GUI
will be to map human suitable graphical objects with list of values.
Bye,
Xavier
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- [Pyatcron-devel-list] Cron and the "*/45" entry,
NICOLOVICI Xavier <=