HHC

Hercules Emulator Prefix

Enhanced Definition

HHC is the standard prefix used by the Hercules mainframe emulator for its console messages, commands, and log entries. It serves to clearly identify output originating from the Hercules software itself, distinguishing it from messages generated by the emulated operating system (like z/OS, MVS, VM, or DOS/VSE).

Key Characteristics

- Standard Identifier: Consistently used by Hercules across all emulated environments to mark its own output and commands.
- Message Origin: Indicates that a message or log entry is internal to the Hercules emulator, providing status, warnings, or errors related to the emulation process rather than the guest OS.
- Command Syntax: Used to issue specific Hercules control commands from the emulated console, allowing users to manage the emulator's state or virtual devices.
- Log Filtering: Facilitates easy filtering of Hercules-specific output in console logs, aiding in diagnosis and monitoring of the emulator's operation.
- Configuration Context: Appears in Hercules configuration files (.conf) and startup messages, indicating parameters being processed by the emulator.

Use Cases

- Issuing Emulator Control Commands: A user might type HHC P on the emulated console to pause the Hercules CPU, HHC R to resume it, or HHC SHUTDOWN to gracefully terminate the emulator.
- Monitoring Emulator Status: Observing log messages like HHC00001I Hercules version ... during startup to confirm the emulator's initialization and configuration.
- Debugging Emulator Issues: Filtering console output for HHC messages to diagnose problems related to Hercules itself, such as device attachment failures (HHC00007E), CPU errors, or network interface issues.
- Managing Virtual Devices: Using commands like HHC ATTACH or HHC DETACH to dynamically add or remove virtual devices (e.g., tape drives, disk volumes) from the emulated environment.

Related Concepts

The HHC prefix is fundamental to interacting with and understanding the Hercules emulator, which itself is a software implementation designed to mimic IBM mainframe hardware. Hercules allows users to run z/OS, MVS, VM, or other mainframe operating systems on non-mainframe platforms (like Windows, Linux). While HHC messages are distinct from z/OS console messages (which might have prefixes like IEF, IEA, DSI, $HASP), they are often seen interleaved on the same emulated console. Users must differentiate between HHC messages (emulator-level communication) and other messages (guest OS-level communication) to correctly interpret system behavior and troubleshoot issues.

Best Practices:

Differentiate Messages: Always distinguish between HHC prefixed messages (originating from the emulator) and other messages (originating from the guest operating system like z/OS) when monitoring or troubleshooting.
Use for Emulator Control Only: Reserve HHC commands strictly for controlling the Hercules emulator's functions, not for managing the guest operating system or its applications.
Log Analysis: When reviewing system logs from an emulated environment, filter by HHC to quickly identify emulator-specific events, errors, or configuration changes, which can be crucial for diagnosing performance or stability issues.
Security and Stability: Be mindful that HHC commands can significantly impact the entire emulated environment. Use them judiciously and understand their implications before execution, especially in shared or critical emulation setups.