IEFUSI

Enhanced Definition

`IEFUSI` is a System Management Facilities (SMF) user exit in z/OS that is invoked by the Job Entry Subsystem (JES2 or JES3) *before* a batch job or started task begins execution. Its primary purpose is to allow sites to define and enforce resource limits, such as CPU time, region size, and output lines, thereby controlling system resource consumption.

Key Characteristics

- Pre-Execution Control: IEFUSI is invoked *prior* to job initiation, providing a crucial point to validate and modify job resource requests before they impact the system.
- Resource Governance: It enables system administrators to implement site-specific policies for resource allocation, preventing runaway jobs and ensuring fair resource distribution.
- Customizable Logic: IEFUSI is a user-written program (typically in Assembler or COBOL) that replaces the IBM-supplied dummy exit, allowing for highly customized resource allocation logic.
- JCL Parameter Override: The exit can inspect and modify JCL parameters like TIME, REGION, LINES, and CARDS specified on the JOB statement, overriding user-supplied values if necessary.
- Job Rejection Capability: Based on defined rules, IEFUSI can reject a job outright if it violates critical resource policies, preventing it from entering execution.
- System-Wide Impact: Once installed, the IEFUSI exit affects *all* batch jobs and started tasks initiated on the z/OS system, making its correct implementation critical.

Use Cases

- Enforcing Resource Limits: Automatically setting or overriding REGION to a standard value (e.g., REGION=0M or REGION=200M) for all jobs, or limiting TIME to prevent long-running processes.
- Cost Allocation and Budgeting: Implementing rules to restrict resource usage for specific user IDs or accounting codes to manage departmental budgets.
- Preventing System Instability: Rejecting jobs that request excessively large REGION sizes or unrealistic TIME limits that could destabilize the system or impact other workloads.
- Standardizing Job Parameters: Ensuring that all jobs conform to site-specific JCL standards, such as requiring a specific MSGCLASS or NOTIFY parameter.
- Prioritizing Workloads: Allowing critical production jobs higher resource limits while imposing stricter controls on development or test jobs.

Related Concepts

IEFUSI works in conjunction with JES (JES2 or JES3) as a critical component of the job initiation process, allowing for pre-execution validation and modification of job parameters. While it is an SMF *user exit*, IEFUSI itself does not generate SMF records; rather, it *influences* the resource consumption that SMF later records for accounting and performance analysis. It complements the Workload Manager (WLM) by providing a first line of defense for resource control *before* a job starts, whereas WLM dynamically manages active workloads based on performance goals. IEFUSI can directly interact with and override parameters specified in JCL statements.

Best Practices:

Thorough Testing: Always test any changes to the IEFUSI exit rigorously in a non-production environment, as errors can impact all batch processing on the system.
Keep Logic Simple: Design the exit with clear, concise logic to minimize overhead during job initiation and simplify maintenance. Avoid complex I/O or extensive processing within the exit.
Comprehensive Documentation: Maintain detailed documentation of the IEFUSI exit's logic, rules, and parameters, including who made changes and why, to aid in troubleshooting and future enhancements.
Version Control: Treat the IEFUSI source code as a critical system component, placing it under strict version control to track changes and facilitate rollback if necessary.
Error Handling: Implement robust error handling within the exit to prevent it from abending, which could lead to system instability or job processing failures.
Performance Monitoring: Regularly review SMF data and system logs to ensure the IEFUSI exit is functioning as intended and that resource limits are appropriately set and enforced.