Problem starting VT Terminal

[Josema-Kyndryl]

We can't get the VT terminal to start. Always return a message Error: Terminal closed due to websocket error. Code=4999

We've configured as:

• Host: 127.0.0.1
• Port: 22
• Type: SSH

The same sequence of messages appears in the ZWESLSTC JobLog after each connection attempt:

- 2026-04-14 08:30:29.112 <ZWED:83951876> ZWESVUSR INFO (org.zowe.terminal.proxy:vtdata,terminalProxy.js:811) ZWED0108I - Saw Websocket request, method=GET       
- 2026-04-14 08:30:29.188 <ZWED:83951876> ZWESVUSR INFO (org.zowe.terminal.proxy:vtdata,terminalProxy.js:494) ZWED0101I - ÝHost=127.0.0.1, Port=22, ClientIP=158.98.42.181~ Connected. Total terminals connected: 1
- 2026-04-14 08:30:29.188 <ZWED:83951876> ZWESVUSR INFO (org.zowe.terminal.proxy:vtdata,terminalProxy.js:505) ZWED0104I - Total VT terminals connected: 1         
- 2026-04-14 08:30:29.323 <ZWED:83951876> ZWESVUSR WARN (org.zowe.terminal.proxy:vtdata,terminalProxy.js:487) ZWED0139W - Host communication error=Cannot read properties of undefined (reading 'data')
- 2026-04-14 08:30:29.324 <ZWED:83951876> ZWESVUSR INFO (org.zowe.terminal.proxy:vtdata,terminalProxy.js:210) ZWED0097I - ÝHost=127.0.0.1, Port=22, ClientIP=158.98.42.181~ Websocket closed. Total remaining terminals connected: 0 
- 2026-04-14 08:30:29.324 <ZWED:83951876> ZWESVUSR INFO (org.zowe.terminal.proxy:vtdata,terminalProxy.js:221) ZWED0100I - Total VT terminals connected: 0         

Any ideas?

• Zowe version: v3.4.1
• z/OS Version: 3.1
• ESM: RACF
• NodeJS version: v22.21.1
• Java version: 21.0.9 2025-10-21

[balhar-jakub]

Hi Josema, I believe you are aware of #2603 and tried the original recommendations in there.

What was the last version where the VT Terminal worked for you, also did you change Node.js version together with the upgrade to the Zowe version?

[Josema-Kyndryl]

Hi Jakub
The truth is that we haven't used the VT for a long time, so I can't confirm if it worked fine before upgrading the versions.
As for the 3270... It works perfectly since I fixed this as recommended:

  gateway:                      
    apiml:                      
      webSocket:                
        connectTimeout: 15000   
        stopTimeout: 30000      
        asyncWriteTimeout: 60000
        maxIdleTimeout: 3600000 
        requestBufferSize: 8192 

But they were different cases. On that occasion, the error message that is now shown in the log did not appear:
Host communication error=Cannot read properties of undefined

[balhar-jakub]

I see, at this stage it looks like intersection of Virtual Desktop and the API Mediation Layer. I would recommend opening case with one of the Conformant Support Providers, I believe you should have such entitlement for at least one of them as this may be tricky issue based on the complexity of the previous one.

Nevertheless, if that is not an option for you, we will need more logs and information on the setup:

• For API Mediation Layer the debug logs can be enabled according to this article - https://docs.zowe.org/stable/troubleshoot/troubleshoot-apiml#enable-api-ml-debug-mode

@struga0258 Is there any debug logs from the Virtual Desktop side that would help? I can see in the documentation the guidelines for collecting the logs here - https://docs.zowe.org/stable/troubleshoot/app-framework/appfw-tracing

[Josema-Kyndryl]

Hi Jakub

I'll attach the ZWESLSTC joblog after restart with components.gateway.debug= true, components.app-server.debug= true & components.app-server.logLevels.org.zowe.terminal.proxy.*=3

ZWESLSTC.ZOSA.D0420.JOBLOG.txt