ERO - Emergency Restart Override

Enhanced Definition

ERO, or Emergency Restart Override, is a CICS (Customer Information Control System) mechanism used during region startup to explicitly dictate the type of restart CICS should perform, overriding its default determination. It is primarily employed after an abnormal CICS termination to ensure proper recovery or to bypass issues preventing a standard emergency restart. ERO (Emergency Restart Override) is a CICS (Customer Information Control System) system initialization parameter that forces a CICS region to perform an **emergency restart**, regardless of the information stored in its catalog files. It instructs CICS to ignore the previous shutdown state and proceed with full recovery processing for in-flight transactions.

Key Characteristics

- Startup Parameter: ERO is typically specified as a parameter during CICS startup, either in the System Initialization Table (SIT) or as an override in the JCL PARM field of the CICS startup job.
- Overrides Default Logic: CICS normally determines the restart type (cold, warm, emergency) based on the state of its system log and control blocks; ERO forces a specific type, such as EMERGENCY or WARM.
- Impact on Recovery: Using ERO directly influences how CICS processes its system log and performs transaction backout or forward recovery for in-flight units of work.
- Data Integrity Risk: Incorrect or ill-advised use of ERO, especially forcing a WARM restart when an EMERGENCY restart is required, can compromise data integrity across CICS-managed resources.
- Common Values: The most common override values are EMERGENCY (to force an emergency restart, even if CICS thinks it's not needed) and WARM (to force a warm restart, potentially skipping emergency recovery).

Use Cases

- Abnormal CICS Termination: When a CICS region terminates unexpectedly (e.g., due to an operating system crash, power failure, or operator CANCEL command) and needs to be restarted to restore service.
- Failed Automatic Emergency Restart: If CICS attempts an automatic emergency restart but fails due to issues like a corrupted system