IHC

Enhanced Definition

`IHC` is the default command prefix used to identify and issue **JES3 (Job Entry Subsystem 3)** operator commands from the z/OS system console or through automation. It signals to the operating system that the subsequent text is a command intended for the JES3 component, distinguishing it from MVS, JES2, or other subsystem commands.

Key Characteristics

- Default Prefix: IHC is the standard, IBM-supplied default prefix for JES3 commands. While it can be customized during JES3 initialization, IHC is widely recognized and used.
- Command Delimiter: When issuing a JES3 command, *IHC (where * is the MVS command character) is typically used. For example, *IHC,D,Q displays the JES3 queue status.
- Scope: It applies exclusively to commands directed at the JES3 component of z/OS, covering job management, device control, and system status within the JES3 environment.
- Operator Interface: Primarily used by system operators and automation programs to interact with and manage the JES3 complex, providing real-time control over job flow and resource allocation.
- Distinction: It serves to prevent command conflicts with other z/OS components that might use similar command syntax but require a different prefix (e.g., $ for JES2 commands).

Use Cases

- Displaying JES3 Status: An operator might issue *IHC,D,Q to display the status of jobs on the JES3 queues (e.g., input, output, execution queues) or *IHC,D,R to show resource status.
- Controlling JES3 Devices: To start or stop a JES3-managed device, such as a printer or card reader, an operator would use a command like *IHC,S,PRT1 (start) or *IHC,F,PRT1 (force stop).
- Managing Jobs: Commands like *IHC,C,JOBNAME can be used to cancel a specific job under JES3 control, or *IHC,H,JOBNAME to hold a job in the queue.
- System Initialization/Shutdown: During JES3 startup or shutdown procedures, IHC commands are used to bring the subsystem online or offline gracefully, managing the transition of jobs and resources.

Related Concepts

IHC is intrinsically linked to JES3 (Job Entry Subsystem 3), serving as its primary command interface. It operates within the broader z/OS operating system environment, where the * (asterisk) is the default character for issuing MVS console commands. Unlike JES2, which uses $ as its default command prefix, IHC specifically targets JES3's unique job scheduling and resource management capabilities, particularly in multi-CPU configurations where JES3 acts as a global scheduler. Understanding IHC is crucial for operators and system programmers managing JES3 complexes, as it allows them to interact directly with the subsystem's internal functions and queues.

Best Practices:

Verify Command Syntax: Always ensure the correct IHC command syntax is used, including parameters and delimiters, to avoid errors or unintended operations that could impact job processing.
Use Authorized IDs: JES3 commands, especially those that alter system state or job flow, should only be issued by authorized personnel or automation routines with appropriate security privileges defined in RACF or equivalent.
Consult Documentation: Refer to IBM's z/OS JES3 Commands manual for a comprehensive list of commands, their