maxssiz(5)							File Formats Manual							maxssiz(5)

NAME

       maxssiz, maxssiz_64bit - maximum size (in bytes) of the stack for any user process

VALUES

   Default
   Allowed values
DESCRIPTION

       User  programs  on  HP-UX  systems  are composed of five discrete segments of virtual memory: text (or code), data, stack, shared, and I/O.
       Each segment occupies an architecturally defined range of the virtual address space which sets the upper limit  to  their  size.   However,
       text, data, and stack segments may have a smaller maximum enforced via the and tunables.

       and  define the maximum size of the stack segment for 32-bit and 64-bit processes.  The stack segment contains the actual program stack and
       the storage space for registers on a process or thread context switch.

   Who is Expected to Change This Tunable?
       Anyone.

   Restrictions on Changing
       Changes to this tunable take effect only for processes started after the modification.  In addition, a process which modifies its  for  the
       stack segment propagates the modified limit to all child processes, thereby exempting them from any future modification of The value speci-
       fied is expected to be a multiple of the base page size. See the description of getconf(1) for more details.  If the value specified is not
       a multiple of the base page size, it will be rounded down to the nearest multiple of the base page size.

   When Should the Value of This Tunable Be Raised?
       should be raised if user processes are generating the console error message:

       Processes generating this error message will likely terminate with the segmentation violation error and dump core.

   What Are the Side Effects of Raising the Value?
       Raising	this  tunable  by  definition  allows larger stack segments for every process.	This means that and function as limitations on the
       amount of swap space that can be reserved or used by each process.  Therefore, using more virtual address space does not translate directly
       to using more physical address space because virtual pages can be swapped out.

       If  swap  space	on  the  machine  is  near capacity, raising this tunable increases the amount of reservable swap per process.	This could
       exhaust the swap space on the system by allowing a process with a memory leak or a malicious program that uses huge amounts  of	memory	to
       reserve too much swap space.

       It  is  also  important	to realize that for 32 bit user processes, data and stack are located contiguously.  Raising the amount of virtual
       address space reserved for the stack segment implies lowering the amount of virtual address space for the data segment.	 In  other  words,
       raising may cause user processes which use all (or nearly all) of the previously available data area to fail allocation with the error even
       with set above the current amount of memory allocated for data by this process.

       On will cause an increase in the kernel data structures used to represent the larger stack space.  This	may  use  enough  additional  swap
       space that the user may see performance degradation or application failure due to lack of reservable swap space.

       One  method to minimize impact is to use a script which launches the applications needing maximum stack size.  Within the script, raise the
       value of launch the application, and then lower to its previous value.  This will allow	the  specific  application  to	benefit  from  the
       increased stack size but will not cause additional stack growth for applications which do not need it.

   When Should the Value of This Tunable Be Lowered?
       This  tunable  should be lowered if swap space is at a premium on the machine and programs that are using too much swap space are affecting
       the execution of other critical user processes.

   What Are the Side Effects of Lowering the Value?
       Lowering this tunable will limit the amount of memory available for stack usage per process.  This could cause processes with  large  stack
       requirements to terminate with a error.

   What Other Tunable Values Should Be Changed at the Same Time?
       The tunable should be considered because it also limits swap usage by process data segment.

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

       getconf(1), maxdsiz(5), maxtsiz(5).

							     Tunable Kernel Parameters							maxssiz(5)