dontdump(5)                                                     dontdump(5)
                          Tunable Kernel Parameters



 NAME    [Toc]    [Back]
      dontdump - defines which classes of kernel memory pages are not 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
      excluded 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 30 = UNUSED + USERPG + KCODE +
      BCACHE.  The kernel chooses these classes because they are not usually
      useful in debugging kernel problems.

 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
      provide a means for restricting kernel dumps to specific types of
      information:





 Hewlett-Packard Company            - 1 -      HP-UX 11i Version 2: Sep 2004






 dontdump(5)                                                     dontdump(5)
                          Tunable Kernel Parameters



            . 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 dontdump 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 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 dontdump.

    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 exclude certain classes of pages
      from being dumped when there is a system crash.  This can be done to
      speedup the dump.





 Hewlett-Packard Company            - 2 -      HP-UX 11i Version 2: Sep 2004






 dontdump(5)                                                     dontdump(5)
                          Tunable Kernel Parameters



    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 alwaysdump tunable should not contain the same page classes as
      dontdump.

 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]
      dontdump was developed by HP.

 SEE ALSO    [Toc]    [Back]
      crashconf(1M), alwaysdump(5).


 Hewlett-Packard Company            - 3 -      HP-UX 11i Version 2: Sep 2004