IKJ56425I: Logon rejected, user ID in use

What it means

Each TSO session runs in its own address space on z/OS, named after the user ID. When you log on, TSO checks whether that ID already has one. If it does, the new logon is rejected with IKJ56425I. The check stops two sessions from working with the same user's data sets and profile at once.

The message names the system where the other session is running, for example already logged on to system SYSB. That system may not be the one you're trying to reach. Older releases worded the same message as USERID IN USE, without the system name.

The other session is usually yours. If an emulator window closes without logging off, or the network drops, the mainframe doesn't always notice straight away. The old session stays active, or waits in a disconnected state in case you come back. Until it ends or you reconnect to it, a fresh logon is refused.

The I at the end of the message number stands for informational. TSO isn't waiting for you to reply.

Common causes

• You closed the emulator window without logging off, or the PC crashed, went to sleep or lost its VPN connection. The old session is still there.
• You're still logged on in another window, on another PC or in a virtual desktop session.
• The previous session is still logging off. Cleanup takes a few seconds, and longer if a command was running.
• You're logged on to another z/OS system that shares the same check. At many sites the check covers every system that shares the JES2 spool, not only the one you're connecting to. The system name in the message tells you which one.
• Someone else is using your user ID. This is rare, but it should be reported.

How to find the problem

1. Look for other emulator windows or sessions on every PC and virtual desktop you use.
2. Wait a minute and try again. If the old session was already ending, the second attempt usually works.
3. If it still fails, call the help desk and give them the system name from the message. Operations staff can check the session on that system with the operator command D TS,PAYU07 or in SDSF.
4. Ask them whether the session is in a disconnected state. If it is, you may be able to reconnect instead of having it cancelled.

How to fix it

• Reconnect if your site allows it. On the full-screen logon panel, put an S in the Reconnect field. In line mode, enter LOGON PAYU07 RECONNECT. You get the old session back with your screen as you left it. This works only on the system that holds the session, while it's disconnected and within the time limit your site sets.
• If reconnecting isn't possible, ask the help desk or operations to cancel the old session. The operator command is C U=PAYU07, entered on the system named in the message. Wait for it to end, then log on again.
• Anything unsaved in the old session is lost when it's cancelled. If you were editing in ISPF with edit recovery on, ISPF offers to recover the member the next time you edit.
• To stop it happening again, log off properly before closing the emulator. Leave ISPF with =X, then type LOGOFF at the READY prompt.
• If you weren't logged on anywhere and the help desk finds an active session, report it to your security team.

What it looks like

LOGON PAYU07
IKJ56425I LOGON rejected, UserId PAYU07 already logged on to system SYSB

Last reviewed 2026-10-12 by the WND Software team. Written in our own words. For the full reference, check IBM’s documentation for your z/OS, CICS or Db2 release.