What are system symbols?

System symbols represent values that are unique to each system. The system replaces system symbols with its own values when it processes started task JCL and batch job JCL (jobs and procedures read from a procedure library), and TSO logons. A started task is a task resulting from JCL that is processed immediately as a result of a START command. Batch job JCL is scheduled by JES2 or JES3 and is run based on system resources and other controls. For additional information about started tasks, see Using symbols in started task JCL. For additional information about batch job JCL, see Using symbols in batch JCL.

The following rules govern the use of system symbols:

To use system symbols in batch JCL, you must first specify SYSSYM=ALLOW on the class definition, and assign the batch job to that class.
You can use system symbols in started task JCL and batch job JCL (for both jobs and procedures), and in TSO logon procedures.
Within started task JCL and batch job JCL, you can use system symbols wherever you use JCL symbols (described under What are JCL symbols?).

Note the following differences between system symbols and JCL symbols:

Substitution texts for system symbols are either fixed for the life of an IPL (static system symbols) or determined by the system (dynamic system symbols).
Substitution texts for JCL symbols can be controlled through input job stream modifications to their definitions.

Before you use system symbols in JCL, see z/OS MVS Initialization and Tuning Reference for a complete list of symbols and for details about how they work. Then read the rest of this section for specific information about using system symbols in started task JCL.