Technical data

2-2 Diagnostic Procedures
2.2 Examining a Frozen System
When a system is frozen, it is either hung or the kernel has panicked. It is important to
determine which case has occurred in the system you are diagnosing because the
procedures for fixing a hang are different from those for fixing a kernel panic.
2.2.1 What to Do If the System Is Still Frozen
Note: The best way to find a system hang or panic is to examine it while it is still frozen.
If the system is at a customer site, this may not be possible, since the customer may
already have reset or rebooted the system. Encourage a customer who is
experiencing hangs or panics to leave the system frozen until you can examine it.
If a customer must reboot a system before you can examine it, ask the customer to
first generate a core dump using a nonmaskable interrupt from the System
Controller. (See Section 4.5.2, “Key Switch in the Manager Position.”) If the
customer does this when the system hangs, you can later examine the core file for
clues to the cause of the problem.
A system can be frozen six basic ways, due to either hardware or software problems, as
shown in Table 2-1:
Only the last condition indicates a hardware error. Deal with the other cases by gathering
appropriate information and filing a bug report.
System Condition Likely Cause
The kernel is under such a heavy disk swapping
load that no processes can run.
Software problem or insufficient system
resources, such as memory and swap space.
The kernel is running out of a software resource
and cannot perform normal process scheduling.
Insufficient system resources, such as kernel
buffers, memory, and swap space.
One or a few processes are hung, but other
processes are running fine.
Software problem.
No processes are running, but the kernel is still
ticking at interrupt level.
Software problem.
Processors are stuck spinning in the kernel;
interrupts are also blocked.
Software problem.
One or more processors are not executing
instructions normally.
Hardware problem.
Table 2-1 Likely Causes of Common System Problems