What are the Normal Abend Codes in MVS?
In the world of Mainframe systems, specifically in the IBM z/OS environment, encountering an abend (abnormal end) code is a common occurrence. These codes are essentially error messages that indicate why a program terminated abnormally. Understanding these codes is crucial for debugging and resolving issues in your MVS applications.
Abend codes provide valuable information about the cause of the failure, allowing you to pinpoint the source of the problem and take appropriate corrective actions.
What are Abend Codes?
An abend code is a system-generated code that appears in the system log or job log when a program terminates abnormally. It usually consists of a four-character code, sometimes followed by a two-digit system completion code (SCC). This code provides valuable insight into the reason for the program failure.
Examples of Abend Codes:
- S0C1: This is a very common abend code indicating a program check, which usually points to a programming error.
- S0C4: This code suggests an access violation, possibly due to incorrect data access or invalid addresses.
- S0C7: This code indicates a program error related to storage allocation.
Normal Abend Codes vs. Abnormal Abend Codes
Abend codes can be broadly categorized as "normal" and "abnormal" codes.
Normal Abend codes are expected termination codes. They indicate a controlled program termination, usually due to a deliberate action or a condition that the program was designed to handle. These codes are often used for normal program exit points or when a program encounters a predefined error condition.
Abnormal Abend codes, on the other hand, signal unexpected program termination. They indicate errors or conditions that were not anticipated or handled by the program, often requiring investigation and debugging.
Common Normal Abend Codes in MVS
Here are some common abend codes that are typically classified as "normal" in MVS:
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S0C1: Program Check. A program check is a type of exception that is detected by the system during the execution of a program. This could be due to various reasons, such as an arithmetic overflow, a divide by zero, or an attempt to access an invalid memory location.
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S0C4: Data Exception. This abend code occurs when there is an error in accessing data. For example, attempting to access a data element that is not defined, or trying to read data from an invalid address.
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S0C7: Storage Violation. This abend code indicates an error in managing storage. It could mean that the program is trying to access storage that is not allocated to it, or that it is trying to allocate more storage than is available.
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S222: Program Terminated by User Action. This abend code indicates that the program was terminated by a user command, such as an operator command or a user-defined exit.
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S322: Program Terminated by the System. This abend code indicates that the program was terminated by the system due to an error, such as a system abend or a timeout condition.
Tips for Understanding Abend Codes
Here are some tips to help you understand and interpret abend codes in MVS:
- Review the system log or job log. The system log and job log often contain detailed information about the abend, including the abend code, the time of the abend, and the program that was running.
- Use the MVS Abend Code Reference. IBM provides a comprehensive documentation that lists all the abend codes and their descriptions. Consult this reference to understand the specific meaning of the code.
- Examine the program code. Carefully inspect the program code in the vicinity of the abend code to identify any potential errors or inconsistencies.
- Use debugging tools. MVS debugging tools can be invaluable for understanding the context of the abend and pinpointing the source of the problem.
Conclusion
Understanding abend codes is essential for maintaining and troubleshooting MVS applications. By familiarizing yourself with common abend codes and their meanings, you can quickly identify the cause of program failures and take appropriate actions to resolve them. Remember that abend codes are valuable clues that can help you pinpoint the source of the problem and improve the reliability of your MVS systems.