Job Card

Enhanced Definition

The Job Card is the first statement in a Job Control Language (JCL) stream, serving as the primary identifier for a batch job submitted to the z/OS operating system. It provides essential job -level parameters, including accounting information, resource requests, and output handling instructions, which govern the job's execution and management by JES (Job Entry Subsystem).

Key Characteristics

- Mandatory First Statement: Every JCL stream must begin with a Job Card, typically in the format //jobname JOB parameters.
- Job Identification: Uniquely identifies the job within the z/OS environment, allowing for tracking, monitoring, and control.
- Resource Allocation: Specifies system resources such as maximum CPU time (TIME) and memory region (REGION) that the job is allowed to consume.
- Output Handling: Controls how job log messages and system output (SYSOUT) are processed and routed, often via the MSGCLASS parameter.
- Priority and Class: Assigns a job class (CLASS) and execution priority (PRTY) which influence when and where the job will run.
- Accounting Information: Includes accounting data (ACCT) for resource chargeback or tracking purposes.

Use Cases

- Submitting Batch Applications: The most common use case, where a Job Card initiates the execution of COBOL programs, utility jobs, or other batch processes.
- Resource Management: System programmers use Job Card parameters like REGION and TIME to prevent jobs from monopolizing system resources or to ensure critical jobs receive adequate allocation.
- Output Routing and Notification: Directing job completion messages and SYSOUT to specific output queues or notifying users (NOTIFY) upon job termination.
- Job Scheduling and Prioritization: Assigning jobs to specific classes or priorities to manage workload and ensure critical jobs run ahead of less urgent ones.
- Restart and Recovery: Specifying a RESTART parameter to allow a job to restart from a specific step in case of failure, improving fault tolerance for long-running processes.

Related Concepts

The Job Card is the entry point for JCL (Job Control Language), defining the overarching context for all subsequent EXEC and DD statements within the job stream. It is processed by JES (Job Entry Subsystem - JES2 or JES3), which uses the Job Card's parameters to queue, schedule, and manage the job's lifecycle from submission to completion. The parameters specified on the Job Card directly influence how z/OS allocates system resources, handles output, and manages the job's execution environment, making it fundamental to system operations and workload management.

Best Practices:

Descriptive Job Names: Use clear, meaningful job names (e.g., PAYROLL01, DB2UTILB) for easy identification and monitoring by operations staff and developers.
Optimize REGION and TIME: Specify realistic REGION and TIME values to prevent resource waste or unnecessary job abends, while ensuring sufficient resources for the job's actual needs.
Utilize NOTIFY: Always include NOTIFY=&SYSUID or a specific user ID to ensure relevant personnel are informed of job completion or failure.
Appropriate MSGCLASS: Select a MSGCLASS that routes job logs to the correct output destination for review, archival, or automated processing.
Consistent CLASS and PRTY: Assign job classes and priorities consistently based on business criticality and resource requirements to optimize system throughput and meet SLAs.
Include ACCT Information: Use the ACCT parameter for accurate resource tracking, chargeback, or departmental reporting, especially in shared mainframe environments.