Capturing system hang information

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 PROM monitor.

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 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.

Let's move on now to the next step, using the savecore program.