JCL EXEC statements: How z/OS finds the program or procedure

To successfully run the program or procedure that you specify on a JCL EXEC statement, z/OS® has to search for and find that program or procedure. Using JOBLIB, STEPLIB, or JCLLIB statements can reduce search time.

Where z/OS searches depends on what you specify in your JCL:

When you code the PGM parameter, z/OS looks for an application program, and will automatically search standard system program libraries, such as SYS1.LINKLIB, which contains IBM-supplied programs. If the program you want to run resides in a private program library, you must specify either a JOBLIB DD statement or a STEPLIB DD statement for z/OS to successfully locate the program.
- When you use a JOBLIB DD statement, insert the JOBLIB DD statement in the job before the first EXEC statement in the job. When you submit the job, z/OS will search any private libraries specified on that JOBLIB DD statement before searching system libraries. z/OS repeats that search order for any programs called within the job.
  For a multi-step job, using the JOBLIB DD statement is most efficient when most of the programs reside in private libraries.
- When you use a STEPLIB DD statement, you may place it anywhere within a job step but it typically appears after the EXEC statement. When you submit the job, z/OS will search the private libraries specified on that STEPLIB DD statement, but only for the one step.
  For a multi-step job, using the STEPLIB DD statement is most efficient when most of the programs reside in system, rather than private, libraries.
When you code the PROC parameter or you omit the PGM or PROC parameter, z/OS looks for a procedure and will automatically search standard system procedure libraries, such as SYS1.PROCLIB. If the procedure you want to run resides in a private library, you must specify the JCLLIB statement for z/OS to successfully locate the procedure.
If a job does not specify a procedure library, the system retrieves all cataloged procedures called by EXEC statements from the procedure libraries defined by the installation for the job's job class. To direct the system to search another procedure library, or to limit the procedure libraries it searches, code a JCLLIB statement that identifies one or more libraries. On a JCLLIB statement, you may list system libraries, installation-defined libraries, or private libraries. The system searches the libraries in the order in which they are specified on JCLLIB.