Changing the master scheduler JCL

When making changes to the master JCL, keep the following in mind:

If you add DD statements to the master JCL, create the associated data sets before you load the initial program that is to use them. If the system cannot allocate a data set that is defined in the master JCL, system initialization fails.
If you specify the START command in the master JCL for the primary job entry subsystem, specify the NOSTART parameter for the subsystem in the IEFSSNxx parmlib member. For the syntax of the NOSTART parameter, see IEFSSNxx (subsystem definitions) - keyword parameter form in this information.
No work can be done that requires JES input or output services until the primary job entry subsystem is started.

To make changes to the master JCL, you can specify an alternate version of the master JCL in one of the following:

A MSTJCLxx parmlib member (recommended)
A MSTJCLxx load module in SYS1.LINKLIB.

If you plan to specify an alternate version of the master JCL in the MSTJCLxx load module in SYS1.LINKLIB, remember that you need to assemble the alternate version and link-edit it into SYS1.LINKLIB each time you make a change. It is easier to change the master JCL when it is specified in the MSTJCLxx parmlib member, because the assemble and link-edit are not required.

Note: IBM® supplies the IEESMJCL member of SYS1.SAMPLIB as an example of alternate master JCL. The CSECT name in IEESMJCL is MSTJCL05. When specifying an alternate version of the master JCL, IBM suggests that you modify IEESMJCL according to your needs. The statements in IEESMJCL are only examples. They are not necessarily the same values that IBM supplies in the default load module MSTJCL00.