alwaysdump(5) alwaysdump(5)
Tunable Kernel Parameters
NAME [Toc] [Back]
alwaysdump - defines which classes of kernel memory pages are dumped
when a kernel panic occurs
VALUES [Toc] [Back]
Failsafe
0
Default [Toc] [Back]
0 (Allow the kernel to choose which classes to dump.)
Allowed values [Toc] [Back]
Integer values from 0 to 1024.
The integer value should be the sum of the integer values for the
included classes as follows:
UNUSED 2 : Unused pages
USERPG 4 : User pages
BCACHE 8 : Buffer cache
KCODE 16 : Kernel text pages
USTACK 32 : Process stack
FSDATA 64 : File-system Metadata
KDDATA 128 : Kernel dynamic data
KSDATA 256 : Kernel static data
SUPERPG 512 : Unused superpage pool
Recommended values [Toc] [Back]
0 (Allow the kernel to choose which classes to dump.)
The value the kernel usually chooses is 480 = KSDATA + KDDATA + FSDATA
+ USTACK.
KSDATA and KDDATA are needed for debugging any kernel problem. FSDATA
is needed for debugging file system problems. USTACK is needed for
debugging problems involving user space applications. UNUSED, USERPG,
BCACHE, KCODE, and SUPERPG are not usually needed for debugging.
DESCRIPTION [Toc] [Back]
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 dontdump and alwaysdump parameters
Hewlett-Packard Company - 1 - HP-UX 11i Version 2: Sep 2004
alwaysdump(5) alwaysdump(5)
Tunable Kernel 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 crashconf command, and its associated configuration file
/etc/rc.config.d/crashconf, 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 alwaysdump and dontdump tunables.
The bit-map value stored in alwaysdump 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 0. 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 alwaysdump.
Who Is Expected to Change This Tunable?
Only HP Field engineers should change the value of this tunable.
Restrictions on Changing [Toc] [Back]
Changes to this tunable take effect at next reboot. Use crashconf 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.
Hewlett-Packard Company - 2 - HP-UX 11i Version 2: Sep 2004
alwaysdump(5) alwaysdump(5)
Tunable Kernel Parameters
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 dontdump tunable should not contain the same page classes as
alwaysdump.
WARNINGS [Toc] [Back]
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 tunable
values, consult the documentation for the kernel software being
installed. For information about optional kernel software that was
factory installed on your system, see HP-UX Release Notes at
http://docs.hp.com.
AUTHOR [Toc] [Back]
alwaysdump was developed by HP.
SEE ALSO [Toc] [Back]
crashconf(1M), dontdump(5).
Hewlett-Packard Company - 3 - HP-UX 11i Version 2: Sep 2004 [ Back ] |