ATNI: Task abended after a terminal error

What it means

For terminals connected through VTAM, CICS terminal control hands every session error to DFHZNAC. That covers a lost session, an unbind, a protocol error or a terminal that was switched off. DFHZNAC decides what to do about the error, writes DFHZC messages describing it, and calls the node error program (DFHZNEP). A site can write its own NEP to change the actions DFHZNAC takes.

One possible action is ABTASK, which abends the task using the terminal. If a task is attached to the terminal when that action is taken, CICS raises the TERMERR condition on the task's current or next terminal control request. A program can handle TERMERR and clean up. If it doesn't, the task ends with ATNI.

So ATNI doesn't point at a bug in the program. It tells you the terminal went away, or misbehaved, while the task was still using it. The details of what went wrong are in the DFHZC messages written at the same time.

Common causes

• A user closed the emulator window, or lost their network connection, while a transaction was running or waiting for input at that terminal.
• The session was lost in the network, for example when a link failed or an operator deactivated the logical unit.
• A terminal or emulator broke the SNA protocol, and the session was ended with a sense code.
• A site-written node error program asked for ABTASK on errors where the default actions would have left the task alone.

How to find the problem

1. Look in the CSNE transient data log for DFHZC messages at the time of the abend. They name the terminal ID and network name and usually give an SNA sense code.
2. Message DFHZC3437I lists the actions DFHZNAC and the node error program took for the error.
3. Find the DFHAC message for the abend in the region's message log to confirm the transaction and terminal.
4. Check the z/OS console and network logs for messages about the same logical unit at the same time.
5. Ask whether your region uses its own DFHZNEP, and if so, what it does for that error.

How to fix it

• Use pseudo-conversational design. A task that ends after each screen holds nothing while the user thinks, so a dropped session between screens abends nothing.
• Fix the network or emulator problem shown by the DFHZC messages and sense codes.
• In programs that need to tidy up when the terminal fails, handle the TERMERR condition. IBM notes this doesn't replace a node error program, which handles session-level problems.
• Review the node error program's actions for the error if the ATNI abends started after it was changed.

Last reviewed 2026-10-18 by the WND Software team. Written in our own words. For the full reference, check IBM’s CICS documentation for your release.