process_id_max(5)						File Formats Manual						 process_id_max(5)

NAME

       process_id_max - limit the maximum value for process IDs (PIDs)

VALUES

   Failsafe
   Default
   Minimum
   Maximum
       must be greater than or equal to If the difference between and inclusive is less than is effectively limited to this difference.

DESCRIPTION

       The tunable allows the administrator to select a potential value range for process IDs (PIDs) as generated by (see fork(2)).  It allows the
       administrator to select a balance between compatibility, capacity, and aesthetics.

       Warning: Some programs cannot tolerate PID values up to the maximum.  If such programs exist and are critical, the maximum  PID	should	be
       appropriately constrained.  For more details on these concerns, see below.

   Who is Expected to Change This Tunable?
       Anyone.

   Restrictions on Changing
       Do not increase the maximum PID if there are critical applications which assume that PIDs fit into a restricted range.  (See below).

       The  value  of  can  be increased at any time, and it takes effect immediately.	(However, its effect may not be noticed until a sufficient
       number of new processes have been created to cause the system to utilize the available higher values.)

       A decrease in the value of also takes effect immediately.  However any existing processes with PIDs that are higher than the new value  are
       not affected.  The decrease will be in full effect for all processes only after a reboot.

   When Should the Value of This Tunable Be Raised?
       Increase  the maximum PID if the range of PIDs defined by the and tunables needs to be increased to allow the creation of more simultaneous
       processes.  See nproc(5) for limits on the number of processes.

       Increase the maximum PID in systems which have many active processes (for example, >25,000).  The larger range may increase the	efficiency
       of creating of new processes (because it may take less work to find available PIDs).

       If  it  is  desired to validate that software programs execute properly in environments where PID values may be large, increase the tunable
       along with the tunable to force all new process IDs to take on large values.  (See process_id_min(5) for more information.)

       Do not increase the maximum PID if there are critical applications which assume that PIDs fit into a restricted range.  (See below.)

   What are the Side Effects of Raising the Value?
       If the difference between and tunables is less than the number of processes allowed to exist simultaneously is limited to that difference.

   When Should the Value of This Tunable Be Lowered?
       Lower the maximum PID if critical applications make assumptions that the PID range is restricted.

   What are the Side Effects of Lowering the Value?
       If the difference between and tunables is less than the number of processes allowed to exist simultaneously is limited to that difference.

   What Other Tunable Values Should Be Changed at the Same Time?
       It may be desirable to change For program development and validation, a change in the tunable may also be needed.

   Potential Application Issues
       The range of PID values has, in the past, been restricted to 0..30,000.	Some programs have built-in assumptions about  this  range.   This
       section briefly describes some of those assumptions.

       Some  application  programs have a built-in assumption that a PID does not exceed 30,000 (which was the old value of the (undocumented) and
       constants).  They could fail if PIDs exceed this maximum.

       Some application programs store PIDs in 16-bit variables (type in C).  Such programs could fail if the maximum PID exceeds 32,767.

       Some programs provide output formats which can be sensitive to the number of digits in the PID.	Such programs  may  produce  aesthetically
       displeasing  output  if PIDs exceed 5 digits (exceed 99,999).  In some cases automatic expansion of output fields can disturb column align-
       ment.  In some other cases, adjacent fields could run together, making the output incomprehensible.

       Some programs or scripts parse the outputs of other programs which contain PID values.  Some such programs have built-in assumptions that a
       PID will not exceed five character positions.  Such a program could fail if the range exceeds 99,999.

       Because	session IDs (SIDs) and process group IDs (PGIDs) are the same as the process ID of the session or group leader, an increase in the
       maximum PID also increases the maximum SID and PGID.  Though much less likely, the same application issues may exist for SIDs and PGIDs.

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.

       The HP-UX kernel may silently round the selected values for and/or (e.g., to the nearest power of 2) in order to accommodate the PID gener-
       ation algorithm.

       Do not increase the maximum PID if there are critical applications which assume that PIDs fit into a restricted range.	See  the  previous
       section,  for  more details on such programmatic assumptions.  The default maximum (30,000) has been selected to provide compatibility with
       all such programs.  This value should be used if program sensitivity to larger PID values is unknown.  See process_id_min(5)  for  informa-
       tion about how large PID values can be selected for software validation purposes.

       Increasing the PID range does not increase the maximum number of processes in the system.

       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

       fork(2), nproc(5), process_id_min(5).

       whitepaper, available on

							     Tunable Kernel Parameters						 process_id_max(5)