Installation guide

Saving Memory Dumps
HP-UX version 11.00.03 Administering Fault Tolerant Hardware 5-41
Saving Memory Dumps
The dump process provides a method of capturing a “snapshot” of what your
system was doing at the time of a panic. When the system panics, it tries to save
the image of physical memory, or certain portions of it. The system automatically
dumps memory when a panic occurs. You can also save a dump manually in the
event of a system hang.
A system dump occurs when the kernel encounters a significant error that causes
a system panic. If the kernel panics, a dump occurs. The system memory is
examined, and all selected pages in use when the system panic occurred are saved.
To help you determine why the system panic occurred (and prevent a
reoccurrence), you should send the dump file to the CAC for analysis.
The system supports the following types of memory dumping:
■ full system dumps—Full system dumps capture the state of all physical
memory and the CPU when the system interruption occurred. This type of
system dump is generally not recommended because it uses too many system
resources.
■ selective system dumps—Selective system dumps capture the state of only
those classes of memory that you specified should be saved in the event of a
system interruption. This type of system dump is recommended.
Before you save a memory dump, you can define the location where dumps will
be saved; otherwise, the dumps will be saved to the default location. The location
you define can be on local disk devices or logical volumes. You also need to ensure
that the location you define has sufficient space to hold the dump.
Understanding How save_mcore and savecrash
Operate
The default dump utility is save_mcore. However, dumps produced using the
Stratus selective save_mcore utility are functionally indistinguishable from those
created using Hewlett Packard’s dumping mechanism, savecrash. The
differences between save_mcore and savecrash are as follows:
■ save_mcore—The save_mcore utility provides an alternative to the typical
sequence occurring when savecrash is used to capture a dump (subsequent
to system failure and prior to reboot). The sequence that occurs when
save_mcore is used as the dump utility is as follows: assuming that the
system is in duplex mode when a panic occurs, the system simply reboots
without capturing a dump, because one of the physical memory copies is left
off line. When the system re-boots, save_mcore automatically saves this
image. Handling dumps through save_mcore improves reboot time and