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All cron jobs randomly firing a bunch of times in parallel?

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7 comments

  • Benjamin D.

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  • cPRex Jurassic Moderator

    Hey there!  I can't say I've heard of such a thing, and I also don't have any other reports of similar behavior that I could find.

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  • Benjamin D.

    It almost feels like some sort of race condition triggers all CPU cores to fire the cron jobs in parallel at the exact same time or something... seemingly at random, but I can list all the date/times where this occurred and I've seen it happen live so I know this is not just written in the logs, it truly brings the server to its knees and I very much have to manually kill all the processes when this happens.

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  • Benjamin D.

    OH BOY.  WTH IS THIS? Is this normal? And how did this happen?! EDIT: I read online that crond forks itself to the amount of scheduled tasks to run.  Is this still the case in AlmaLinux 8.9? Am I panicking for nothing here or is this abnormal? I ran the command again after some time and now there are only 2 crond processes, so I think it's normal that the amount of crond processes varies throughout the day, depending on scheduled cron jobs.  https://support.cpanel.net/hc/en-us/community/posts/19634192633879-Multiple-crond-instances

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  • cPRex Jurassic Moderator

    I would expect the number of processes to vary throughout the day - I wouldn't expect them to be firing the crons multiple times. 

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  • Benjamin D.

    Yeah me neither and I've never seen that happen under CentOS 7 last year, before I upgrade to a new server under AlmaLinux 8 and WHM 116.

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  • Benjamin D.

    It just happened again.  133 cron jobs (same 8 or 9 crons multiplied by a bunch of parallel instances) of all kinds across the entire server all fired up at the same time, using most of Apache's slots, since they're basically just calling an HTTP request each, denying normal web browser traffic for a few minutes until I managed to kill the processes.  I almost couldn't sign in to WHM to do so.  I'm now wondering if it would be a bug caused by when WHM auto-updates itself?

    For future reference, this happened under WHM 118.0.4, let's see if the next time it happens is under a newer version or not.

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