KCS - Kernel Crash Dump System

Enhanced Definition

The Kernel Crash Dump System (KCS) is a critical diagnostic facility within the z/OS operating system designed to automatically capture the state of the system's kernel (supervisor) and associated address spaces when a severe, unrecoverable system error or `abend` occurs. Its primary purpose is to provide comprehensive diagnostic data for deep-level problem determination and resolution, particularly for issues impacting the core functionality of z/OS.

Key Characteristics

- Automatic Invocation: KCS is typically invoked automatically by the z/OS supervisor when a critical system error (e.g., 0C4, 0C1, 0C6 abends in supervisor state, or other severe wait states) is detected, ensuring vital diagnostic data is captured without manual intervention.
- Supervisor State Focus: It specifically targets and captures the contents of the MVS kernel (the supervisor's address space), key system control blocks, and often the address spaces of tasks that were active or involved at the time of the crash.
- Dump Dataset Generation: The output of a KCS dump is written to pre-allocated dump datasets (typically SYS1.DUMPxx datasets), which are sequential datasets formatted to hold the captured system image.
- System Impact: While capturing a dump, the system's normal operations are paused or significantly impacted, potentially leading to a wait state or system termination, depending on the severity of the error.
- Comprehensive Data: KCS captures a vast amount of information, including CPU registers, main storage contents, PSW (Program Status Word), control registers, segment and page tables, system queues, and trace tables, all crucial for deep-level problem analysis.
- Customizable Scope: While primarily automatic, the scope of what is included in a dump can be configured via CHNGDUMP commands or the IEADMP00 parmlib member, allowing administrators to specify which address spaces or data spaces should always be included.

Use Cases

- Diagnosing System Abends: When the z/OS system experiences a severe abend (e.g., 0C4, 0C1, 0C6 in supervisor state, or 0A9 abends), KCS captures the necessary data to determine the root cause, such as an invalid instruction,