dontdump(5)dontdump(5)NAMEdontdump - defines which classes of kernel memory pages are not 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
excluded 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 = The kernel chooses these
classes because they are not usually useful in debugging kernel prob‐
lems.
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 capabili‐
ties 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
not 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 exclude certain classes of pages
from being dumped when there is a system crash. This can be done to
speedup the dump.
What Are the Side Effects of Turning the Tunable On?
If pages necessary for analyzing the dump are excluded, then the dump
may not be useful for identifying the cause of the system crash.
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 not be dumped based on
the type of crash. The dump may take longer.
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 parame‐
ter 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 val‐
ues. For information about the effects of installation on tunable val‐
ues, 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 ALSOcrashconf(1M), alwaysdump(5).
Tunable Kernel Parameters dontdump(5)
