Steps for setting process limits in z/OS UNIX

Before you begin, you need to understand how the MVS™ limits affect z/OS® UNIX processes. For an explanation of soft and hard limits, see What are hard limits? and What are soft limits?. You can modify some limits. Parameters are provided by batch JCL, TSO logon, and started to limit region size and high memory. Some MVS system-wide limits such as MEMLIMIT are initially set in SMFPRMxx.

You also need to have planned the system-wide limits that will affect all z/OS UNIX users. For more information, see Defining system limits.

Perform the following steps to set process limits in z/OS UNIX.

1. Determine the sources that your installation uses to control MVS limits and z/OS UNIX limits. For more details, see Tuning limits in BPXPRMxx. For more information about limiting the use of memory objects, see Limiting the use of memory objects in z/OS MVS Programming: Extended Addressability Guide.

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2. Specify the z/OS UNIX system-wide limits in BPXPRMxx. The system-wide limits are listed in Table 1. If you do not set them, defaults are used. To look up the defaults, see BPXPRMxx (z/OS UNIX System Services parameters) in z/OS MVS Initialization and Tuning Reference.

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3. Specify higher limits for individual processes, if needed. For an explanation about setting process limits in general, see Setting limits for users. For a discussion of the use of MEMLIMIT, see Limiting the use of memory objects in z/OS MVS Programming: Extended Addressability Guide.
   You can use any of the following to change z/OS UNIX limits:

   • The SETOMVS operator command
   • z/OS UNIX programming APIs
   • RACF®
   • z/OS UNIX commands
   • setrlimit
   • spawn()

   You can use the RACF ADDUSER and ALTUSER commands to specify the ASSIZEMAX limit on a per-user basis. Table 3 lists the process limits that you can set.

   To define or change information in the OMVS segment of a user profile, including your own, you must have the SPECIAL attribute or at least UPDATE authority to the segment through field-level access checking.

   For more information about the OMVS segment in RACF user profiles and a complete list of what you can specify, see The OMVS segment in group profiles in z/OS Security Server RACF Security Administrator's Guide.

   Resource values that processes receive when they are dubbed a process will use the RACF profile to determine the hard limit if it is higher than the soft (current) limit. It is also used when processes are initiated by a daemon process using an exec after setuid(). In this case, both the RLIMT_AS hard and soft limits are set to the address-space-size value

When you are done, you have set process limits in z/OS UNIX.