The primary subsystem

MVS™ requires that at least one subsystem be defined as a job entry subsystem (JES) to bring jobs into the system. The JES that you select, which can be either JES2 or JES3, is called the primary subsystem. If you do not specify an IEFSSNxx member in SYS1.PARMLIB, MVS attempts to use the system default member, IEFSSN00. IEFSSN00, as supplied by IBM®, contains the definition for the default primary job entry subsystem, JES2.

Note: Your JES primary subsystem name must match the procname that is used to start JES.

If you attempt to IPL without specifying an IEFSSNxx member and IEFSSN00 is not present or does not identify the primary subsystem, the system issues message IEFJ005I (see Handling Initialization Errors) and prompts the operator for the primary subsystem.

For an IPL, do not define a subsystem more than once in a combination of IEFSSNxx members that can be used together or within a single member. (The same subsystem can appear in two different IEFSSNxx members when the members will not be used together.) In general, if MVS detects a duplicate name, both of the following are true:

MVS does not define the duplicate subsystem
MVS does not give control to the initialization routine.

The system issues the following message:

     IEFJ003I:  DUPLICATE SUBSYSTEM subname NOT INITIALIZED