Cron Question

[RW]

On Tue, 2 Sep 2008 11:40:37 -0500
Dan Nelson <dnelson at allantgroup.com> wrote:


> I use the lockfile command ( from the procmail port ) to ensure that
> recurring cron jobs don't overlap if one run takes too long. For
> example, to run mrtg on a 1-minute cycle but prevent multiple mrtgs
> from running if one run takes longer than 1 minute:
> 
> * * * * * /usr/local/bin/lockfile -r 1 -l 3600 /tmp/mrtg.LCK &&
> ( nice -19 /usr/local/bin/mrtg /usr/local/etc/mrtg/mrtg.cfg ;
> rm /tmp/mrtg.LCK )
> 
> The -l 3600 tells lockfile to remove any lockfiles over an hour old (
> if the machine was rebooted during an mrtg run for example )
> 
you could also handle stale lock-files, without installing procmail,
like this:

   LCK=/tmp/foo.LCK
   find $LCK -mtime +3600s -delete
   if ![ -f "$LCK" ] ; then
       touch "$LCK"
       [ -f "$LCK" ] && foo 
       rm "$LCK"
   fi

Presumably the lockfile command also eliminates the race between testing
for, and creating, the lock-file, but that's not really needed here.