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KnowledgeBase 00021: Managing User Numbers

Last updated: 22 Jul 2016
Applies to: All versions
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How User Numbers Are Allocated

By default, user numbers cycle around from 1 to 1023, each new process being allocated the next available user number in rotation. The upper limit of this cycle will increase for licences that permit more than 1023 processes.

This cyclic user number allocation was chosen so that log files, etc that are generated using the user number as part of their name do not promptly get overwritten by a new process. It also makes it easier to see if a process is still running.

It is recommended that applications should not assume anything about how user numbers work.


Controlling User Numbers

Because some users want control over allocation user numbers, there are four configuration parameters that affect this mechanism...

FIXUSERS=u,n
Reserves a pool of n user numbers starting at u that will only be allocated to processes entering QM from the operating system shell with a command line of the form
    qm -123
where 123 is the desired user number.

PHANTOMS=u,n
Reserves a pool of n user numbers starting at u that will only be allocated to phantoms started with a command line of the form
    PHANTOM USER 123
where 123 is the desired user number.

PORTMAP=p,u,n
Reserves a pool of n user numbers starting at u that will only be allocated to users logging on from a series of n consecutively numbered telnet ports starting at port p.

USERPOOL=n
Sets the upper limit of the cycling user number range (default 1023).

Only one process can run as any user number at one time. Attempts to use any of the above mechanisms to start process with a user number that is already in use will fail.


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