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Old 07-21-2007, 05:54 PM   #1
Registered: Aug 2006
Location: England Somewhere
Distribution: Mandriva, PCLinuxOS, Karoshi, Suse, Redhat, Ubuntu
Posts: 518

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Question Cron job or Sleep timer??? Which is best in my situation

Well basically, firstly the question is i was looking into a cron job running every so many seconds, but it seems the best available i can see is every minute, unless there is a way to do it??? say if possible show me an example of setting a cron job for something that runs every 20 seconds.


At the moment in my scripts i just use a sleep timer to cause the required delay, and then let it loop basically.

What i want to know is what would cause the greater over heads (CPU wise) and be the most reliable.
A cron job that executes every 20 seconds and then the script exits, or a script in a constant loop that will just sleep for 20 seconds?? Does the sleep command use any overheads or is it more like the command isn't in execution anyway?

Thanks for any info
Karoshi Team
Old 07-21-2007, 05:59 PM   #2
Registered: Jun 2006
Location: Mariposa
Distribution: Slackware 9.1
Posts: 938

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First, I'm fairly sure that the cron job would take more overhead than the simple sleep loop.

Second, if the job is being run once every 20 seconds, the difference in overhead won't matter at all.

Third, if the interval itself is critical, don't sleep for 20 seconds, but sleep for as long as it takes to start the job 20 seconds after the last time it started.

Fourth, when I read the man page for crontab I don't see any granularity finer than one minute.

Hope this helps.
Old 07-21-2007, 06:08 PM   #3
Registered: Aug 2006
Location: England Somewhere
Distribution: Mandriva, PCLinuxOS, Karoshi, Suse, Redhat, Ubuntu
Posts: 518

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Excelent thanks, i got asked to change my already sleep timed scripts to be put into cron, couldn't see much point in it myself wanted to make sure it didn't matter much



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