Job Number

Enhanced Definition

In z/OS, a **job number** is a unique identifier assigned by the Job Entry Subsystem (JES) to every batch job, started task (STC), and TSO user session upon its initiation. It serves as a primary key for JES to track, manage, and control the execution and output of these work units within the system.

Key Characteristics

- Uniqueness: Each job number is unique within a JES spool for a given period, ensuring no two active or recently completed jobs share the same identifier.
- Format: Typically an alphanumeric string, often in the format JOBnnnnn for batch jobs, STCnnnnn for started tasks, or TSUnnnn for TSO user sessions, where nnnnn is a sequential number.
- Assignment by JES: The Job Entry Subsystem (JES2 or JES3) is solely responsible for assigning job numbers as jobs enter the system queue.
- Persistence: A job retains its assigned job number throughout its lifecycle, from submission to execution and until its output is purged from the spool.
- System-Wide Identification: It provides a consistent way for operators, system programmers, and other system components to refer to a specific instance of work.

Use Cases

- Monitoring Job Status: Using tools like SDSF (System Display and Search Facility) or JES commands (e.g., D A,L) to check the current status (e.g., HELD, ACTIVE, OUTPUT) of a particular job.
- Managing Job Output: Locating and viewing the SYSOUT (system output) datasets associated with a specific job, often identified by the job number.
- Job Control: Issuing JES commands (e.g., C J=JOBnnnnn to cancel, H J=JOBnnnnn to hold) to manage individual jobs precisely.
- Auditing and Logging: System logs and accounting records often include the job number to provide an audit trail for executed work.
- Problem Determination: When a job abends, its job number is crucial for identifying the specific execution instance, retrieving its dump, and analyzing its output for debugging.

Related Concepts

The job number is intrinsically linked to JES (Job Entry Subsystem), which is the component responsible for its assignment and management. While a JCL (Job Control Language) JOB statement defines a job's name and parameters, it is JES that assigns the unique job number upon submission. It works in conjunction with the job name (specified in JCL) to provide a complete identifier; the job name identifies the *type* of work, while the job number identifies a *specific instance* of that work. Tools like SDSF heavily rely on job numbers for displaying and interacting with active and completed jobs and their associated SYSOUT datasets.

Best Practices:

Utilize for Precision: Always use the job number when performing critical operations like canceling or holding jobs to ensure the correct instance is affected, especially if multiple jobs share the same job name.
Monitor Critical Jobs: For long-running or critical production jobs, note their job numbers for quick reference and monitoring via SDSF or automated monitoring tools.
Understand Job Name vs. Job Number: Educate users on the distinction: the job name is defined in JCL, while the job number is assigned by the system and is unique to an execution instance.
Leverage SDSF Filters: Use job numbers in