Each time you start a JES2 subsystem, MVS™ establishes JES2 as an authorized subsystem address space and gives control to JES2 to initialize itself through the following procedures:

• Begin the JES2 procedure through either an operator command (S JES2) or an IPL-time automatic process such as the COMMNDxx members of SYS1.PARMLIB. Then MVS:
  • locates the JES2 procedure in SYS1.PROCLIB.
  • allocates the libraries to which the DD statements in the JES2 procedure point, including those that the JES2 subsystem uses to locate the JES2 initialization statements.
  • gives control to the JES2 subsystem, which establishes the JES2 general ESTAE protection before calling a series of initialization routines (IRs), as follows, to process each phase of JES2 initialization.
• Process the start options specified and call installation Exit 0, allowing the installation to perform pre-initialization processing.
• Process the current status of the subsystem interface (SSI), establishing necessary control blocks and preparing for later SSI requests.
• Allocate various control blocks required during all JES2 processing or temporarily during initialization processing.
• Process the initialization statements specified through parmlib, console, and exit routine input, and call installation Exit 19 for each initialization statement.
• Process the initialization statements specified, verifying the validity of the parameters and calculated variable parameters. These post-processing functions include:
  • General processing and verifying the complete set of initialization statements and their parameters (specified and defaulted)
  • Calculating variable parameters based on other parameter values
  • Validating the parameters specified and the associated control blocks.
• Allocate the control blocks required to:
  • Define the devices specified through the initialization statements
  • Allow I/O activity for the defined devices
• Process the initialization and perform validation, as required for JES2 network job entry (NJE) activity.
• Process the initialization and perform validation, as required for JES2 remote job entry (RJE) activity.
• Validates the current JES2 direct access devices (DASD) that are defined through the initialization statements, analyzes the spool volumes and the checkpoint data sets (whether they reside on DASD volumes or Coupling facility structures), and performs any required related activities (such as checkpoint data set forwarding).
• Validates the multi-access spool (MAS) configuration specifications.
• Allocate common storage control blocks for command and message traffic, MVS initiator support, the subsystem interface (SSI), the JES2 trace facility, and other JES2-supported facilities.
• Connect the JES2 devices defined through the initialization statements to MVS device control blocks.
• Call miscellaneous MVS services (for example, to establish interfaces).
• Allocate the control blocks necessary to define those JES2 processors that are required immediately after initialization that cannot be dynamically added later.
• Generate the information string for the request subsystem (SSI) version call 54 routine.
• Complete JES2 initialization by building the required buffer pools and calling installation Exit 24 (post-initialization exit routines).