alwaysdump(5) File Formats Manual alwaysdump(5)
NAME
alwaysdump - defines which classes of kernel memory pages are dumped when a kernel panic occurs
VALUES
Failsafe
Default
(Allow the kernel to choose which classes to dump.)
Allowed values
Integer values from to
The integer value should be the sum of the integer values for the included classes as follows:
2 : Unused pages
4 : User pages
8 : Buffer cache
16 : Kernel text pages
32 : Process stack
64 : File-system Metadata
128 : Kernel dynamic data
256 : Kernel static data
512 : Unused superpage pool
Recommended values
(Allow the kernel to choose which classes to dump.)
The value the kernel usually chooses is =
and are needed for debugging any kernel problem. is needed for debugging file system problems. is needed for debugging problems involving
user space applications. and are not usually needed for debugging.
DESCRIPTION
On large systems, the time required to dump system memory when a kernel panic occurs can be excessive or even prohibitive, depending on how
much physical memory is installed in the system. Fast-dump capabilities controlled by the and parameters provide a means for restricting
kernel dumps to specific types of information:
. Unused Physical Memory
. User Process
. Buffer Cache
. Kernel Code
. Process Stack
. File-System Metadata
. Kernel Dynamic Data
. Kernel Static Data
. Unused Superpage Pool
The command, and its associated configuration file control which of these memory classes are to be included in the memory dumps associated
with a kernel panic. On rare occasions, the system may panic before crashconf(1M) is run during the boot process. On those occasions, the
configuration can be set using the and tunables.
The bit-map value stored in specifies which of these memory classes are to be included in the memory dumps associated with a kernel panic.
The default value for this parameter is The system determines whether or not to dump classes of memory based on the type of crash that
occurs, in this case.
Note that certain types of system crash, require a full crash dump. Also, the system operator may request a full crash dump at the time
the dump is taken. In either of these cases, a full dump will be performed regardless of the classes selected using
Who Is Expected to Change This Tunable?
Only HP Field engineers should change the value of this tunable.
Restrictions on Changing
Changes to this tunable take effect at next reboot. Use to change the selection of pages to take effect immediately.
When Should the Tunable Be Turned On?
This tunable should be turned on to include certain classes of pages in the dump when there is a system crash.
What Are the Side Effects of Turning the Tunable On?
If pages unnecessary for analyzing the dump are included, then the dump will take longer.
When Should the Tunable Be Turned Off?
The tunable is turned off by default.
What Are the Side Effects of Turning the Tunable Off?
The system decides the page classes that must be dumped based on the type of crash.
What Other Tunables Should Be Changed at the Same Time?
The tunable should not contain the same page classes as
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of
HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation,
some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun-
able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was
factory installed on your system, see at
AUTHOR
was developed by HP.
SEE ALSO
crashconf(1M), dontdump(5).
Tunable Kernel Parameters alwaysdump(5)