IBM AS/400 - Setup Telnet 5250 Server

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Table of contents :

Introduction

The IBM AS/400 provides interactive access to the system through 5250 terminals. Traditionally this was done using Twinax terminals (like the InfoWindow II), but with the arrival of TCP/IP support, IBM introduced a telnet server to allow 5250 sessions over the network.

In this article, we will see how to configure and start the Telnet 5250 service on an AS/400 9401-150 running OS/400 V4R4, so that users can connect with 5250 emulators remotely.

Requirements

Before enabling the Telnet server, make sure that:

  • TCP/IP is configured and active on your AS/400 (see this article on TCP/IP configuration)
  • You can log in with security officer authority (QSECOFR)
  • A 5250 emulator (such as Mocha TN5250, tn5250j, or IBM Access Client Solutions) is available on your workstation

Starting TCP/IP

First, ensure that TCP/IP is active. You can check the status with:

WRKTCPSTS

If it is not active, start it:

STRTCP

Starting the Telnet server

The Telnet server is managed as a TCP/IP server job named QTVTELNET, which normally runs inside the subsystem QSYSWRK.

To start it, use:

STRTCPSVR SERVER(*TELNET)

You can confirm it is running with:

WRKACTJOB SBS(QSYSWRK)

Look for a job named QTVTELNET.

Enabling interactive subsystem

Telnet sessions require the interactive subsystem QINTER to be active. If it is not running, start it with:

STRSBS SBSD(QINTER)

Without QINTER, users will not receive a sign-on screen.

Allowing virtual terminals

Telnet 5250 sessions use virtual display devices named QPADEVxxxx. The system value QAUTOVRT controls how many such devices can be created.

Check its value with:

DSPSYSVAL QAUTOVRT

If it is 0, no Telnet sessions can be created. Change it to a reasonable value (for example, 200):

CHGSYSVAL SYSVAL(QAUTOVRT) VALUE(200)

Allowing QSECOFR authority to login remotely

By default, the Telnet server does not allow the QSECOFR authority to login remotely. Check system value QLMTSECOFR to see if it is set to *NO.

Display it:

DSPSYSVAL QLMTSECOFR

If it is set to 1, change it to 0 (the single quotes are important in the command):

CHGSYSVAL SYSVAL(QLMTSECOFR) VALUE('0')

Testing the connection

From your workstation, start a 5250 emulator and connect to the AS/400 IP address on port 23.

If everything is configured correctly, you should see the sign-on screen:

At this point, you can log in with a valid AS/400 user profile.

Autostarting Telnet at IPL

To avoid manually starting Telnet after each IPL, you can configure it to autostart.

Method 1: Network server configuration

Enable autostart for the Telnet server:

CHGNETSVR SERVER(*TELNET) AUTOSTART(*YES)

Verify with:

WRKNETSVR

Method 2: Startup program

Alternatively, add the Telnet start command to the system startup program:

  1. Check the startup program:
    DSPSYSVAL QSTRUPPGM
  2. Edit the CL program (usually QSYS/QSTRUP)
  3. Add:
    STRTCPSVR SERVER(*TELNET)
    after STRTCP

This ensures that Telnet starts automatically whenever the system IPLs.

References