Introduction

JES2 is a general job entry subsystem of z/OS® and sometimes cannot satisfy all installation-specific needs at a given installation. If you modify JES2 code to accomplish your specific functions, you then are susceptible to the migration and maintenance implications that result from installing new versions of JES2. JES2 exits allow you to modify JES2 processing without directly affecting JES2 code. In this way, you keep your modifications independent of JES2 code, making migration to new JES2 versions easier and making maintenance less troublesome.

Figure 1. Support statements. The figure includes support statements for JES2.

Attention!

Defining exits and writing installation exit routines is intended to be accomplished by experienced system programmers; the reader is assumed to have knowledge of JES2.

If you want to customize JES2, IBM suggests that you use JES2 installation exits to accomplish this task.

IBM does not recommend or support alteration of JES2 source code. If you assume the risk of modifying JES2, then also assure your modifications do not impact JES2 serviceability using IPCS. Otherwise, IBM® Level 2 Support might not be able to read JES2 dumps taken for problems unrelated to the modifications.

Avoid expanding JES2 control blocks. Use alternatives such as:

Use fields dedicated for installation use that appear in many major control blocks. Place your data, or a pointer to your data, in these fields. However, beware of setting storage addresses in checkpointed or SPOOL–resident control blocks.
Use $JCTX services rather than modifying $JCT.
Use table pairs and dynamic tables. For example, use dynamic $BERTTABs with CBOFF=* instead of modifying $JQE.

This is a partial list. Evaluate your specific situation and take appropriate action.

Note!

JES2 operates in full–function mode (z2 mode under z/OS). All discussion in this information assumes JES2 is running in z2 mode. Refer to JES2 exit migration considerations for migration topics.

Figure 2, and the text that follows it, illustrates many of those areas where you can modify JES2 processing using the JES2 exit facility:

Figure 2. Areas of JES2 modification

Initialization Processing
You can modify the JES2 initialization process and incorporate your own installation-defined initialization statements in the initialization process. Also, you can change JES2 control blocks before the end of JES2 initialization.
Job Input Processing
You can modify how JES2 scans and interprets a job's JCL and JES2 control statements. Also, you can establish a job's affinity, execution node, and priority assignments before the job actually runs.
Subsystem Interface (SSI) Processing
You can control how JES2 performs SSI processing in the following areas: job selection and termination, subsystem data set OPEN, RESTART, allocation, CLOSE, unallocation, end-of-task, and end-of-memory.
JES2-to-Operator Communications
You can tailor how JES2 communicates with the operator and implement additional operator communications for various installation-specific conditions. Also, you can preprocess operator commands and alter, if necessary, subsequent processing.
Spool Processing
You can alter how JES2 allocates spool space for jobs.
Output Processing
You can selectively create your own unique print and punch separator pages for your installation output on a job, copy, or data set basis.
JES2-SMF Processing
You can supply to SMF added information in SMF records.
RJE Processing
You can implement additional security checks to control your RJE processing and gather statistics about signons and signoffs.