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I recently installed Munin on my servers. Now 2 of my machines show big spikes in DiskIO at the same time, everyday at 4am.

I run Centos 5.6 (64bit). I've checked my cron logs, and I have no personal scripts running around those times. Also, my hoster does not take backups, as I run my own backups, but they run at 1AM, not 4AM.

My Question is: Does CentOS run any scheduled processes that can take up this much DiskIO?

enter image description here

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up vote 3 down vote accepted

Yes, 0402 is when a ton of system-maintenance cron jobs kick off; it's normal. expected, and harmless. In /etc/crontab you should find the entry that says

02 4 * * * root run-parts /etc/cron.daily

If you want to change the kickoff time, alter those first two figures accordingly. If you want to see what they're doing, perhaps with a view to seeing what all that IO activity is, look in /etc/cron.daily. Don't stop them from running!

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Ah that explains it. Thank you! – Mr.Boon Aug 24 '11 at 11:10

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