maxssiz, maxssiz_64bit - maximum size (in bytes) of the stack for any
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 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
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.
SEE ALSOgetconf(1), maxdsiz(5), maxtsiz(5).
Tunable Kernel Parameters maxssiz(5)