What are hard limits?

The hard limit is the maximum value that a process's application can raise a soft limit to. The hard limit is derived from z/OS UNIX or RACF®.

Use BPXPRMxx statements to define z/OS UNIX defaults. Defaults exist for z/OS UNIX processes even when none are defined in BPXPRMxx. To find out what the defaults are, see the BPXPRMxx topic in z/OS MVS Initialization and Tuning Reference.
Limits defined in the RACF user profile. See Table 3 for a list of hard limits that are defined in the RACF user profile.

z/OS UNIX mechanisms that affect limits are setrlimit(), inheritance from the parent and spawn inheritance structure (BPXYINHE), identity change, and dubbing. Any process can raise the soft limits to the hard limits. A superuser can raise both the hard and soft limits. A fork/spawn child inherits the same limits unless the parent changed the limits in the spawn inheritance structure or there is an identity change. The SETOMVS operator command can also affect these settings.