Customizing the nucleus region

You can use the NUCLSTxx member of SYS1.PARMLIB or the NMLDEF macro to customize the nucleus region. Both are interfaces to the generalized nucleus loader, which:
  • Enables you to maintain, as separate members in SYS1.NUCLEUS, modules to be loaded into the DAT-ON nucleus region
  • Eliminates the need to link-edit, into an IEANUC0x member of SYS1.NUCLEUS, new nucleus-resident code such as installation-written SVCs.

You can design each NUCLSTxx parmlib member or nucleus module list (NML) to contain a list of the SYS1.NUCLEUS members that are part of the same product or user modification. The generalized nucleus loader processes all NMLs found in SYS1.NUCLEUS, including those used by IBM® products and vendor products.

Note:
  1. All multiple CSECT load modules, such as IEANUC0x, to be loaded into the nucleus region, must be link-edited with the scatter (SCTR) attribute. If this is not done, the system enters a non-restartable wait state at system initialization.
  2. Neither the NUCLSTxx parmlib member nor the NMLDEF macro can be used to change the contents of IEANUC0x. They can be used only to specify which additional members of SYS1.NUCLEUS are to be loaded into the nucleus region along with IEANUC0x. See Removing existing routines from IEANUC0x for information on deleting routines from IEANUC0x.

The NUCLSTxx parmlib member is easier to use and offers more flexibility than the NMLDEF macro. See z/OS MVS Initialization and Tuning Reference for more information about NUCLSTxx.

Parent topic: The nucleus