How to find the cause of a hang

Eirik Øverby ltning at
Tue Aug 17 22:31:17 PDT 2004

On 14. Aug 2004, at 22:50, Julian Elischer wrote:

> Eirik Øverby wrote:
>> Hi all,
>> I'm currently experiencing frequent (about once per week) hangs of a 
>> server that is about 1500 kilometers away from me. I have a serial 
>> cable on the box, and using minicom on the neighbor box I am now in 
>> the kernel debugger - but I'm at a complete loss as to what to do to 
>> figure out what is, in fact, wrong.
>> Calling panic or boot doesn't work - it just stops at "syncing 
>> disks..." and never actually reboots. I suspect something fishy going 
>> on with disk I/O, but I can't be certain of that.
>> The box responds to ping - until I call panic or boot - but no other 
>> services are working.
> try capture a stack trace "tr"

Looks like the box is "idle"

> if you have KTR enabled do "show ktr"

This is 4.x... As my follow-up msg on current@ indicated (yes i posted 
to the wrong list initially ;)

> do "ps"

An insane number of cron processes.. Is it trying to run scheduled jobs 
and fails because of the hang?

> do show pcpu
> show witness
> show locks

No workie on 4.x...

> if you have a dump device define..
>   call doadump

No dump device here (if disk is the problem, it would be of no use I 
guess), and i get undefined symbol anyway.

> then to reboot..
>    "call cpu_reset"

Now that one is handy. ;)

> The dump will appear after the next boot in /var/crash
> if it's not big enough for a complete ram dump, symlink it to 
> somewhere where there is enough room.

(See above)

> when you have all that.. let us know :-)

I have what I have. See
(it is too long to include in a mail...

Got any clues for me?


>> What can I do? I'm now at the db> prompt ... Help :)
>> /Eirik
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