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Infodoc ID   Synopsis   Date
11837   How to force a crash when my machine is hung?   23 Feb 1996

Description Top

How do I force a crash when my machine is hung?

In most cases, a system crash dump of a hung system can be forced.
However this is not guaranteed to work for all system hang conditions.
 
To force a dump, you need to drop down to the boot PROM monitor, suspending all
current program execution.  On Sun systems using Sun monitors for the console,
this suspension is done via what is referred to as "L1-A".  L1 was the label
on the earlier Sun keyboards for the top left key on the console keyboard.  
On the newer keyboards, this key is labelled "Stop".  Some keyboards are 
labelled both ways.  While holding down the L1 key, you press the A key.  On 
systems using ASCII terminals for the console, usually the Break key can be
used to get to the boot PROMmonitor.

Depending on the boot PROM that you have, the boot PROM monitor will respond 
with:

Type b (boot), c (continue), or n (new command mode)
>

OR:

Type 'go' to resume
ok

or simply:

>

If you don't see one of these messages, you were probably not successful in
stopping the system.

If you find you are at the > prompt, enter 'n' to get into the new command
mode which will give you the ok prompt.  Once at the ok prompt, enter sync.
The system will immediately panic.  Now the hang condition has been converted
into a panic, so an image of memory can be collected for later analysis.  The
system will attempt to reboot after the dump is complete.

If you have an older Sun that doesn't have the new command mode, enter g0 at
the > prompt.

Both the sync and the g0 commands force the computer to illegally use location
0, thus forcing a panic: zero.

Not all hang situations can be interrupted.  If L1-A or Break doesn't work,
sometimes a series of the same will do the trick.  Some hangs are even more 
stubborn and can only be interrupted by physically disconnecting the console
keyboard or terminal from the system for a minute.

If all these attempts fail, you will have to power down the system, thus 
sadly losing the contents of memory.  With luck, a subsequent hang will be
interruptible.

NOTE: On the Sun4d architecture be sure the key is not in the 
      secure position ( this disables the break interrupt in the zs 
      driver).

*******************************************************************************
This document is an excerpt from a SunSoft publication
Panic! 
by Chris Drake and Kimberly Brown
ISBN 0-13-149386-8

SOLUTION SUMMARY:
Product Area Kernel
Product hang
OS any
Hardware any

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