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CLASS & MSGCLASS Narrative

This page explains the function of the CLASS= and MSGCLASS= keyword operands.

In a JES2 environment, the MSGCLASS operand dictates the output class to be used by three system data sets, which are dynamically allocated and not controlled via DD statements. The data sets are:

• JESMSGLG - JES Job Log
• JESJCL - the JCL listing
• JESYSMSG - Allocation / termination messages.

JOB Statement purpose (1) - narrative

CLASS=

In a z/OS JES2 environment, before resources can be allocated the JOB has to be scheduled for execution and this is the function of the CLASS operand.

If the JOB Statement CLASS operand does not equate to a class supported by any initiator, the job will not be scheduled for execution.

Traditionally there are 36 classes, all the letters (A-Z), and the numbers (0-9). JOBs are selected for execution by matching the CLASS value to the class list in the initiators, with the JOB being scheduled into the first inactive initiator with a matching class. The order of classes dictates the priority of scheduling.

MSGCLASS=

This uses the same range of classes as the CLASS operand, but is used to direct output such as the JCL Listing and system messages. It DOES NOT influence application program listings unless directed by the relevant DD statement SYSOUT operand.