maxssiz man page on HP-UX

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maxssiz(5)							    maxssiz(5)

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

   Allowed values
       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?

   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

       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 mem‐
       ory 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

       On will cause an increase in the kernel data structures used to	repre‐
       sent 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.

       All HP-UX kernel tunable parameters are release specific.  This parame‐
       ter may be removed or have its meaning changed in  future  releases  of

       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

       was developed by HP.

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

			   Tunable Kernel Parameters		    maxssiz(5)

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