WTO - Write to Operator

Enhanced Definition

WTO (Write To Operator) is a fundamental z/OS service that allows application programs, system components, and utilities to send messages directly to the system console operator. Its primary purpose is to inform the operator about system events, job status, error conditions, or to request specific actions, ensuring operational awareness and control.

Key Characteristics

- Programmatic Interface: WTO can be invoked from various programming languages, including Assembler, COBOL, PL/I, and C/C++, using a specific macro or API call.
- Message Routing: Messages can be directed to specific operator consoles or groups of consoles using routing codes, allowing for targeted communication based on the message's origin or importance.
- Descriptor Codes: Each message can be assigned descriptor codes (0-16) that indicate its urgency, type (e.g., action required, eventual action, informational), and whether it should be retained on the console.
- Message ID and Text: WTO messages typically include a unique message ID (e.g., IEF234I, ARC0001I) followed by descriptive text, providing context and often suggesting an action.
- System Log Integration: All messages issued via WTO are automatically written to the SYSLOG (System Log), providing a historical record of system events for auditing and problem determination.
- No Reply Expected: Unlike WTOR (Write To Operator with Reply), WTO is a one-way communication; the issuing program does not pause or expect an immediate response from the operator.

Use Cases

- Job Status Reporting: A batch COBOL program might issue a WTO to indicate the start, completion, or abnormal termination of a critical processing step.
- Error Notification: A CICS transaction or DB2 stored procedure could use WTO to alert the operator about a severe error, such as a database connection failure or an out-of-storage condition.
- Resource Availability: A system utility might issue a WTO to inform the operator that a specific resource (e.g., a tape drive, a dataset) is needed or has become available.
- Security Alerts: An RACF exit routine or security monitoring tool could issue a WTO to report suspicious activity or unauthorized access attempts.
- Application Health Monitoring: A long-running application might periodically issue WTO messages to confirm its ongoing operation or report internal state changes.

Related Concepts

WTO is intrinsically linked to the z/OS Operator Console and the SYSLOG. All messages issued via WTO appear on the console and are recorded in the SYSLOG for historical tracking. It is often discussed in conjunction with WTOR (Write To Operator with Reply), which is a similar service but designed for two-way communication where the program pauses, awaiting an operator response. WTO messages are frequently the input for z/OS automation tools like SA z/OS or NetView, which intercept, analyze, and automatically respond to specific messages, reducing manual operator intervention.

Best Practices:

Clarity and Conciseness: Ensure message text is clear, concise, and provides sufficient information for the operator to understand the situation and take appropriate action.
Standard Message IDs: Use consistent and documented message IDs, adhering to established naming conventions within your organization or application.
Appropriate Routing and Descriptor Codes: Select routing codes to direct messages to the most relevant console(s) and use descriptor codes to accurately reflect the message's urgency and required action.
Avoid Message Flooding: Do not issue excessive or redundant WTO messages, as this can overwhelm the operator console and obscure critical alerts.
Design for Automation: Structure WTO messages to be easily parsable by automation tools, using consistent formats and keywords to facilitate automated responses.
Documentation: Document all custom WTO messages, including their meaning, potential causes, and recommended operator actions, in an operations manual.