process_id_max.5 (2010 09)

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process_id_max(5) process_id_max(5)

(Tunable Kernel Parameters)

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

process_id_max

and process_id_min

tunables is less than nproc, 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

nproc. For program development and validation, a change in the

process_id_min

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

MAXPID (undocumented) and

PID_MAX constants). They could fail if PIDs exceed this

maximum.

Some application programs store PIDs in 16-bit variables (type

short 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 alignment. 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 pro-

grams 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

process_id_max

and/or

process_id_min (e.g., to the nearest power of 2) in order to accommodate the PID generation algo-

rithm.

Do not increase the maximum PID if there are critical applications which assume that PIDs ﬁt into a res-

tricted range. See the previous section, Potential Application Issues , for more details on such program-

matic 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 information 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 parame-

ter 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://www.hp.com/go/hpux-core-docs

AUTHOR

process_id_max was developed by HP.