From owner-freebsd-questions  Sun Jan  2 21: 3: 4 2000
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Date: Sun, 2 Jan 2000 23:02:56 -0600 (CST)
From: Ryan Thompson <freebsd@sasknow.com>
To: Mitch Collinsworth <mkc@Graphics.Cornell.EDU>
Cc: freebsd-questions@FreeBSD.ORG
Subject: Re: Huge crontab jobs are not run 
In-Reply-To: <200001030033.TAA07780@benge.graphics.cornell.edu>
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On Sun, 2 Jan 2000, Mitch Collinsworth wrote:
> 
> >> > Did you kill -HUP cron?  If you didn't do this (or reboot the system),
> >> > your job won't run.  
> >> 
> >> According to the manpage, you don't need to:
> >> 
> >> | Additionally, cron checks each minute to see if its spool directory's
> >> | modtime (or the modtime on /etc/crontab) has changed, and if it has, cron
> >> | will then examine the modtime on all crontabs and reload those which have
> >> | changed.  Thus cron need not be restarted whenever a crontab file is mod-
> >> | ified.  Note that the crontab(1) command updates the modtime of the spool
> >> | directory whenever it changes a crontab.
> >
> >Hmm... I stand corrected :-)  I haven't looked at than man page for quite
> >some time.  Anyway, kill -HUP can't hurt, and might actually kick a few 
> >things into shape if modtimes get set incorrectly :-)
> >
> ><ASIDE> 
> > Isn't checking all crontabs every minute kind of a waste of good
> > resources in many cases?
> 
> I guess you *still* haven't looked at cron(8) in quite some time.  It
> also states that the every minute check is done on the modtime of the
> directory containing the per-user crontabs and the individual files
> are only checked if the directory modtime has changed.  So in the
> typical nothing-has-changed case, only two checks are done, one on
> /etc/crontab and one on the spool directory.
> 
> Anything else we can read to you?  :-)
> 
> -Mitch

Ha!  It looks like *you* didn't read the rest of my message :-)  I did
indeed read both cron(8) and parts of cron.c to confirm / clarify the
built-in behaviour. Only after doing that did I post my message and state
that there was no obvious way to disable the checks without source
modifications.

Even the "nothing-has-changed case", as you mentioned, still has two
superfluous checks if and only if changes are summoned with kill -HUP. I'm
not terribly worried about it, but I tend to be a bit of an optimization
fanatic sometimes... always looking for something to tweak a bit :-)  For
most sysadmins, removing the checks would just mean another kill -HUP to
forget and flood -questions about.  For me, though, it's something to muck
around with for a while when I need a break from DBI :-)

--
  Ryan Thompson <ryan@sasknow.com>
  50% Owner, Technical and Accounts
  Phone: +1 (306) 664-1161

  SaskNow Technologies     http://www.sasknow.com
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