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Old 03-08-2012, 03:01 AM   #1
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Registered: Mar 2012
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Unhappy Multiple instances of crond - what are the implications?


I have a few scripts scheduled to run at different time of a day.
Sometimes I see multiple instance of cron daemon i.e one daemon has spawned another one and one of them is hung.
For example

root@localhost:/opt/fgw_instance_running/tools/SystemStats# ps -eaf | grep -i "cron"
root 5096 1 0 Mar06 ? 00:00:00 crond
root 15013 5096 0 08:01 ? 00:00:00 crond
root 15020 15013 0 08:01 ? 00:00:00 /bin/bash /usr/bin/run-parts /etc/cron.hourly

Can you please let me know why this may happen and how to resolve this?

Old 03-08-2012, 03:12 AM   #2
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What makes you think it's hung? Just because the process was started on March 6?

Here's a look at my system:
user@localhost$ uptime
 02:14:23 up 19 days,  5:59,  3 users,  load average: 1.00, 1.89, 2.75
user@localhost$ date
Thu Mar  8 02:15:02 CST 2012
user@localhost$ date -d 'today - 19 days - 5 hours - 59 minutes'
Sat Feb 17 20:15:46 CST 2012
user@localhost$ ps -eaf | grep -i "cron"
root      1586     1  0 Feb17 ?        00:00:01 /usr/sbin/cron
As the output shows, the crond daemon was started the last time my system was booted. I suspect that it will remain active until the system is turned off. Just because a process is "old" does not necessarily mean it has "hung."

Last edited by Dark_Helmet; 03-08-2012 at 03:20 AM.
Old 03-08-2012, 03:29 AM   #3
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Thanks for the quick reply.
It mean one of the scripts run by crond was hung, not crond itself. Sorry my bad.
Let me clarify.

I have a job(shell script) scheduled to run every 1 hour. This script will check the size of a directory every hour and if the size is greater than 500Mb, that dir is archived. I have this script running normally for weeks now.
Sometimes this script may take more time to complete the taring and meanwhile crond is spawned again(as you can see in above post). The new crond has the ppid of previous crond.
One of this crond is inactive(meaning, when I restart the cron using /etc/init.d/crond stop, only one of the process is stopped).
Also, is it ok to have multiple instance of crond? I checked the source of crond and there already is a mechanhism to prevent invocation of a instance when there is already one running.
Hope I am clear with my issue.


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