My production server is running Apache v2.2.4 with mod_mono v1.2.4 on CentOS release 5.2 (Final).

Suddenly, Apache service hung during normal usage time (approx. 1 pm EDT). Traffic is not too high at this time. This is the first time we're noticing this kind of behaviour in our server. I noticed from access log that even subsequent requests are also not received, even though there were incoming requests. I then manually tried to invoke my application call from web browser, it never returned successfully but it was still loading.

I found no unusual behaviour/activity in:
1) Apache access_log and error_log
2) No kernel level errors found in /var/log/messages

I've no other option but ended up restarting Apache service.

Any idea on what would cause Apache to hang and thereby not allowing subsequent incoming requests? How do I debug/diagnose when this happens next time?

Experts advice/recommendation on this are highly appreciated.


I have encountered this when there is a block on IO in the kernel. Is the Apache perhaps serving data from an NFS mount or something similar that can fail hard?

  • In my case, I don't think this is a block in IO. Regarding serving of data, my Apache is serving data from within my server drive which is attached permanently, and this is not a NFS mount. – Gnanam Jun 18 '10 at 9:05

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