system hangup - I'm lost

[Robert Watson]

On Tue, 30 Sep 2008, Gavin Atkinson wrote:

> On Mon, 2008-09-29 at 22:14 +0200, Oliver Lehmann wrote:
>
>>   Any idea what I could do to shed some more light on this behaviour?
>>   Why it is happening and what really is causing it?
>>   Would enabling the kernel debugger really help here? I mean the system
>>   is really hanging up - except ping response it is not responding to
>>   anything except the reset switch ;)
>
> If it's responding to ping, you should be able to get into the debugger. 
> Compile it in, along with "options WITNESS" and "options WITNESS_SKIPSPIN", 
> and press ctrl-alt-escape when the machine next hangs.
>
> From there, it should hopefully be possible to get more info.  It's been a 
> long time since I've used the debugger under 6.x so some of the more useful 
> commands may not exist, but the output of at least "sh locks", "sh alllocks" 
> and "bt" on any processes that seem to be holding locks. Also "sh pcpu" and 
> "ps" will help to determine exactly what was running at the time.

"show lockedvnods" is also quite useful if the problem originates in the file 
system, as it lists vnodes that have been locked, and by which threads.

Robert N M Watson
Computer Laboratory
University of Cambridge