IEFSSNxx (subsystem definitions) - keyword parameter form

Note: IBM® suggests that you use the keyword parameter form of the IEFSSNxx parmlib member, which is described here. However, the positional parameter form of the IEFSSNxx parmlib member is still supported. See IEFSSNxx (subsystem definitions) - positional parameter form for more information. Subsystems defined in the keyword parameter form of the IEFSSNxx parmlib member can use dynamic SSI services, while subsystems defined in the positional form of the IEFSSNxx parmlib member cannot use dynamic SSI services. See z/OS MVS Using the Subsystem Interface for more information about dynamic SSI services.

IEFSSNxx contains parameters that define the primary subsystem and the various secondary subsystems that are to be initialized during system initialization. IEFSSNxx allows you to:

Name the subsystem initialization routine to be given control during master scheduler initialization.
Specify the input parameter string to be passed to the subsystem initialization routine.
Specify a primary subsystem name and whether you want it started automatically.
Specify whether the initialization routines for the subsystem are to run in parallel.

For information about writing subsystems, see z/OS MVS Using the Subsystem Interface.

Unless you are starting the Storage Management Subsystem (SMS), specify the primary subsystem (JES) first. Some subsystems require the services of the primary subsystem in their initialization routines. Problems can occur if subsystems that use the subsystem affinity service in their initialization routines are defined before the primary subsystem. If you are starting SMS, specify its record before you specify the primary subsystem record.

Before z/OS® V1R12, the order in which the subsystems were defined depended on the order in which they were specified in the IEFSSNxx parmlib member on the SSN parameter. Beginning with z/OS V1R12, you can specify the BEGINPARALLEL statement that allows the initialization routines for any subsystem that supports parallel processing to be invoked in parallel. For the SMS subsystem or any subsystem that does not support parallel processing, be sure to specify the BEGINPARALLEL statement after you specify the subsystem definitions. For the SMS subsystem, if the BEGINPARALLEL statement is encountered before the SUBSYS statement, the system issues message IEF009E about potential errors. See the BEGINPARALLEL statement in Statements/parameters for IEFSSNxx.

The format of the IEFSSNxx record for SMS is described in Defining SMS through the IEFSSNxx member.

Note: In general, it is a good idea to make the subsystem name the same as the name of the member of sys1.proclib used to start the subsystem. If the name does not match, you may receive error messages when you start the subsystem.