Telnet is a terminal emulation program for TCP/IP networks that allows you to access another computer on the Internet or local area network by logging in to the remote system. Telnet is a client-server protocol used to establish a connection to Transmission Control Protocol port number 23. You can also check open ports on a remote system using Telnet.
In this tutorial, we will learn how to install and use Telnet Server and Client on Ubuntu 20.04 LTS server.
WARNING: Telnet is an unencrypted and therefore insecure protocol. This tutorial exists for educational reasons only and not as a recommendation to use Telnet Server on your system. This guide shows you how to install and use the Telnet client and server in case you are interested in learning more about this ancient server management protocol or in case you want to use the Telnet client to test your mail server. We do NOT recommend using Telnet (Server) on servers today, especially not when using it over the internet. To manage your server over the network, use SSH instead of Telnet. Using a Telnet client is something different, a telnet client is a useful tool to e.g. test your mail or web server as shown below.
- A server running Ubuntu 20.04 server.
- A non-root user with sudo privileges.
- A static IP address 192.168.0.100 configure on your server.
Install Telnet Server
By default, Telnet server package is available in the Ubuntu 20.04 default repository. You can install it by just running the following command:
sudo apt install telnetd -y
Once the installation is completed, you can check the status of Telnet service using the following command:
sudo systemctl status inetd
? inetd.service - Internet superserver Loaded: loaded (/lib/systemd/system/inetd.service; enabled; vendor preset: enabled) Active: active (running) since Mon 2021-04-29 10:24:05 UTC; 38s ago Docs: man:inetd(8) Main PID: 2883 (inetd) Tasks: 1 (limit: 1114) CGroup: /system.slice/inetd.service ??2883 /usr/sbin/inetd Apr 29 10:24:05 ubuntu2004 systemd: Starting Internet superserver... Apr 29 10:24:05 ubuntu2004 systemd: Started Internet superserver.
Test Telnet Connection from Remote System
Telnet server is now installed and listening on port 23. It’s time to connect Telnet server from the remote system.
Now, log in to another Ubuntu system and run the following command:
You will be asked to enter your username and password. After successful authentication, you should see the following output:
Trying 192.168.0.100... Connected to 192.168.0.100. Escape character is '^]'. Ubuntu 20.04 LTS ubuntu2004 login: hitesh Password: Welcome to Ubuntu 20.04 LTS (GNU/Linux 5.4.0-72-generic x86_64) * Documentation: https://help.ubuntu.com * Management: https://landscape.canonical.com * Support: https://ubuntu.com/advantage System information as of Thu 29 Apr 2021 09:16:14 AM UTC System load: 0.83 Usage of /: 14.7% of 39.12GB Memory usage: 30% Swap usage: 0% Processes: 163 Users logged in: 0 IPv4 address for ens33: 192.168.0.100 IPv6 address for ens33: 2003:e1:bf4b:8b00:20c:29ff:fef5:ee3c * Pure upstream Kubernetes 1.21, smallest, simplest cluster ops! https://microk8s.io/ 8 updates can be installed immediately. 0 of these updates are security updates. To see these additional updates run: apt list --upgradable Last login: Wed Apr 28 08:50:37 2021 from 192.168.0.20
You can now run any command on Telnet server using Telnet.
Use telnet to Test Open Ports
You can also use Telnet to test open ports on a remote system.
For example, to test port 80 on the remote system (IP 192.168.0.100) run the following command:
telnet 192.168.0.100 80
If port 80 is open, you should see the following output:
Trying 192.168.0.100... Connected to 192.168.0.100. Escape character is '^]'.
If port 80 is blocked or the Telnet service is not running. You should see the following output:
Trying 192.168.0.100... telnet: Unable to connect to remote host: Connection refused