System limits and process limits

Limits can be set for the system (system-wide limits) or for individual processes (process limits).

System-wide limits, which are limits that apply to every process, are set in the BPXPRMxx member of SYS1.PARMLIB. You can display limits defined in BPXPRMxx by using the operator commands D OMVS,OPTIONS and D OMVS,LIMITS.

Limits associated with an MVS™ application derive their value from MVS. The soft and hard limit might be different when an MVS unit of work is dubbed.
Limits for processes initiated by z/OS UNIX that cause an identity change, such as telnet, rlogin or a daemon process using setuid or exec, are created with the same hard and soft limits.

Process limits are limits that apply to individual processes. You can set some process limits by using the RACF® user profile segment. Some process limits, such as the disk space, allow for a file or the size of a dump are set in BPXPRMxx.

You can control the amount of resources used by specified z/OS® UNIX users by setting individual limits for these users, as described in Setting limits for users. These limits apply to all users except for those with a UID of 0. Normally, when a process is initially dubbed, the soft limit is inherited from MVS and the hard limit is set in the BPXPRMxx parmlib member.
For more information about UID(0) superuser authority, see Obtaining security information about users. Users with UID(0) will still have a limit but they can change it while other users can only change their soft limits.
You can set limits on a process for resources such virtual storage space after you know which resources the application will need, and how the operating system affects application limits. For information about the types of processes and how they are created, see Setting process limits in z/OS UNIX.
You can use the RACF ADDUSER and ALTUSER commands to specify the ASSIZEMAX limit on a per-user basis. See the topic on limiting the use of memory objects in z/OS MVS Programming: Extended Addressability Guide, which discusses the use of MEMLIMIT. Table 3 lists the process limits that you can set.

Before setting process limits as described in Setting process limits in z/OS UNIX, you need to understand how z/OS UNIX applications interact with the operating system and take into consideration all services that affect that resource. Then you can decide what soft and hard limits the application needs. For an explanation soft and hard limits, see What are hard limits? and What are soft limits?.