Introduction
IBM i is designed to handle multiple processes efficiently through its job management and work management system. IBM i uses subsystems, jobs, and job queues to manage workloads dynamically. This guide introduces the basics of IBM i job management, helping beginners understand how processes are handled and controlled.
1. Understanding Jobs in IBM i
A job in IBM i is a unit of work that the system processes. It can be a user session, a background task, or a system function.
Types of Jobs:
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Job Type
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Description
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Interactive Job
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A job initiated by a user signing in via a terminal (e.g., a 5250 session).
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Batch Job
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A background process that runs without user interaction, typically used for reports or updates.
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System Job
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Internal IBM i jobs that handle system processes (e.g., memory management, logging).
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Autostart Job
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A job that starts automatically when a subsystem starts.
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Communication Job
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A job handling network requests (e.g., FTP, Telnet).
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Common Commands for Working with Jobs:
- WRKJOB JOB(USERNAME) – Work with a specific job.
- DSPJOB – Display details of a job.
- ENDJOB JOB(JOBNUMBER) – End a job.
- SBMJOB CMD(CALL PGM(PROGRAM)) JOB(MYBATCHJOB) JOBQ(QBATCH) – Submit a job to batch processing.
2. Subsystems: The Heart of Job Management
A subsystem is an IBM i component that manages jobs. Different subsystems are used to separate workloads and optimize performance.
Common Subsystems in IBM i:
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Subsystem
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Purpose
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QINTER
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Handles interactive user sessions.
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QBATCH
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Manages batch jobs.
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QSPL
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Manages spooled print jobs.
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QCMN
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Handles communication-related jobs.
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QCTL
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Primary system control subsystem.
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Common Commands for Subsystems:
- WRKSBS – Work with subsystems.
- STRSBS SBSD(QINTER) – Start a subsystem.
- ENDSBS SBS(QBATCH) OPTION(*IMMED) – End a subsystem immediately.
- WRKACTJOB – View active jobs in all subsystems.
3. Job Queues and Output Queues
Job Queue (*JOBQ)
A job queue holds jobs that are waiting to be processed by a subsystem.
- Jobs are submitted to a queue before they execute.
- A subsystem picks up jobs from its assigned queue and runs them.
Output Queue (*OUTQ)
An output queue stores spooled files (print jobs) until they are printed or deleted.
Common Commands for Queues:
- WRKJOBQ JOBQ(QBATCH) - Work with jobs in a job queue.
- WRKOUTQ OUTQ(QPRINT) - Work with print jobs in an output queue.
- CHGJOB JOB(USERNAME) RUNPTY(50) - Change job priority.
4. Work Management and Job Priorities
IBM i assigns priorities to jobs to ensure that critical processes get system resources first.
Job Priority Levels:
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Priority
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Impact
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1-9
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Highest priority (used for system-critical tasks).
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10-39
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High-priority jobs, such as interactive user tasks.
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40-99
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Lower priority (batch jobs, reports).
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Changing Job Priorities:
- Set priority when submitting a job: SBMJOB CMD(CALL PGM(MYPGM)) JOBQ(QBATCH) RUNPTY(40)
- Change priority of a running job: CHGJOB JOB(JOBNUMBER) RUNPTY(20)
5. Best Practices for Job Management
1. Use Separate Subsystems for Workload Distribution
- Assign batch jobs to QBATCH instead of running them in QINTER.
- Use custom subsystems for different departments or applications.
2. Monitor and Manage Active Jobs
- Use WRKACTJOB to check for high CPU or long-running jobs.
- End inactive or hung jobs using ENDJOB.
3. Optimize Job Scheduling
- Automate job execution with Job Scheduler (WRKJOBSCDE).
- Set run priorities based on workload importance.
4. Clean Up Spooled Files Regularly
- Delete old spooled files to free up system resources:
- DLTSPF FILE(QPRINT)
5. Restrict User Access to Critical Subsystems
- Limit access to QCTL and other critical subsystems.
- Use job descriptions (*JOBD) to control job behavior.
Conclusion
IBM i job management is built around jobs, subsystems, and queues, ensuring efficient workload processing. Understanding these concepts helps administrators and users optimize performance, manage workloads, and keep the system running smoothly