What is best method to debug freezes/hangs?

Derek Ragona derek at computinginnovations.com
Wed Dec 5 04:17:19 PST 2007

At 08:49 PM 12/4/2007, yar wrote:

>My question is how best to go about debugging sporadic freezes and hangs.
>Just looking for general methods.    On a couple of our IDS systems there
>are sporadic hangs or freezes that occur every couple weeks or so, that are
>recoverable by either system reboots or taking out and reinserting the Gig
>fiber ethernet sniffing cables, but I  never can find anything in
>/var/logs/messages to tell what is going on. I'm assuming that may have to
>compile in kernel debugger support, but from what I read briefly, doesn't
>that require an actual crash with the resultant reboot and a debugger
>readable file  left in /var/crash?  That doesn't happen, there is no
>automatic reboot just a freeze/hang (box falls off network and at the
>console unable to type until one of the two above mentioned measures are
>take. The systems are:
>Dell 1850's
>Free BSD 6.2
>2 Gb ram
>running various open source IDS software  BRO

I would be sure your systems are running the generic kernel, or as close to 
generic that is possible to rule out anything you could have introduced by 
running a custom kernel.

I would also run complete diagnostics on the hardware to rule out any 
hardware issues.

You can also gather some information by having a script run top 
periodically and logging this to a file to see what the system is 
doing.  You can check the last log entry of this file after a freeze/hang 
to see what was going on.


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