How to use telnet linux

Using Telnet in Linux

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1. Overview

The telnet command is a user interface to the TELNET protocol. We can use the telnet command to manage a remote machine using the command line.

It’s similar to the ssh command. The difference is that ssh uses encryption, whereas telnet sends information in plain text. To sum up, ssh is much more secure, and using telnet is not recommended.

2. Installing Telnet

To use telnet, we need to have the Telnet client installed on the local machine and the Telnet server installed on the remote machine. After that, we can use the local machine to connect to the remote machine.

2.1. Installing Telnet Client

To install telnet on the local machine, we can use package managers like yum and apt:

$ sudo yum install telnet # On CentOS, Fedora, and RHEL $ sudo apt install telnet # On Ubuntu/Debian 

2.2. Installing Telnet Server

To install the Telnet server, we should run:

$ sudo yum install telnet-server # On CentOS, Fedora, and RHEL $ sudo apt install telnetd # On Ubuntu/Debian

Now we’ve installed telnet on both machines.

3. Configurations

Before we can use telnet, we need to make some configurations.

3.1. Starting the Telnet Service

We need to start the telnet service on the remote machine:

$ sudo systemctl start telnet.socket # On CentOS, Fedora, and RHEL 

It’s worth mentioning that on Ubuntu/Debian machines, inetd is the service that listens on all ports used by Internet services such as FTP, POP3, and telnet. And, it starts automatically at boot. So we don’t need to start it.

Moreover, we can make the telnet service start at boot by running this command:

$ sudo systemctl enable telnet.socket # On CentOS, Fedora, and RHEL

Now let’s make sure the service is running. On Ubuntu/Debian, we should run:

$ systemctl status inetd inetd.service - Internet superserver Loaded: loaded (/lib/systemd/system/inetd.service; enabled; vendor preset: enabled) Active: active (running) since Mon 2022-07-04 02:50:13 +03; 1s ago 

On Red Hat-based Linux distributions:

$ systemctl status telnet.socket telnet.socket - Telnet Server Activation Socket Loaded: loaded (/usr/lib/systemd/system/telnet.socket; enabled; vendor preset: disabled) Active: active (listening) since Mon 2022-07-04 01:27:28 UTC; 2s ago

The telnet service is up and running.

3.2. Allowing the Telnet Port Through the Firewall

Next, we need to allow the telnet port (23 by default) through the firewall on the remote machine. On CentOS, Fedora, and RHEL, we should run:

$ sudo firewall-cmd --permanent --add-port=23/tcp success 

Then reload the firewall for the changes to take effect:

$ sudo firewall-cmd --reload success

And on Ubuntu/Debian, we should run:

$ sudo ufw allow 23/tcp Rules updated Rules updated (v6) 

$ sudo ufw reload Firewall reloaded

Now we’ve successfully allowed the telnet port through the firewall.

3.3. Creating a New User for Telnet

By default, root is not allowed to login through telnet for security reasons. Hence, we need to create a new user on the remote machine:

After that, we should set a password for it:

$ sudo passwd telnet Changing password for user telnet. New password: Retype new password: passwd: all authentication tokens updated successfully.

We’ve successfully configured telnet on the remote machine.

4. Using Telnet

To connect to the remote machine from the local machine, we should run telnet in the following pattern:

$ telnet -l [username] [remote machine IP] [port (optional)]

$ logout Connection closed by foreign host.

After that, we’ll be back at our local machine.

5. Conclusion

To sum up, we learned how to install and use telnet on a Linux machine. As we discussed, ssh is much more secure than Telnet. So we should use ssh instead of Telnet whenever possible.

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How to Use telnet Command in Linux?

Home » Networking » How to Use telnet Command in Linux?

The telnet command (short for teletype network) utilizes the telnet network protocol to connect to remote machines and manage them through a TCP/IP network. The protocol uses port 23 to establish a connection and provides a way to manage remote systems using the CLI.

Although telnet is similar to SSH, the two are different because SSH is a much more secure option as it uses encryption. telnet , on the other hand, sends data without encryption, making it an easy target for hackers.

In this tutorial, you will learn to use the telnet command in Linux.

• A system running Linux (for Windows users, learn about telnet on Windows).
• An account with root privileges.
• Access to the terminal (Ctrl+Alt+T).

Installing Telnet in Different Linux Distributions

Depending on the Linux distribution you are using, follow the steps below to download and install telnet .

CentOS, Fedora, and RHEL

CentOS, Fedora, and RHEL use yum (Yellowdog Update Manager) as the primary package manager. Follow the steps below:

1. Update the system package repository to make sure the latest version is installed:

2. Run the following commands to install telnet and the telnet server packages required for it to function properly:

sudo yum install telnet telnet-server -y

The command installs the two packages. The -y flag automatically answers Yes to any prompts during the installation.

3. After the installation completes, start and enable the telnet service by running:

systemctl start telnet.socket systemctl enable telnet.socket

4. Allow the telnet port (the default port is 23) through the firewall on the remote machine. Run the following command:

sudo firewall-cmd --permanent --add-port=23/tcp

5. Reload the firewall to apply the changes:

The telnet port is now allowed through the firewall.

Ubuntu and Debian-Based Distributions

Ubuntu and other Debian-based distributions use the apt package manager by default. Follow the steps below to install telnet :

1. Update the system package repository:

2. Run the following command to install telnet :

sudo apt install telnetd -y

Wait for the installation to complete. The service should start automatically.

3. Check if telnet is properly installed by running:

sudo systemctl status inetd

The output shows that the daemon is up and running.

4. Allow port 23 through the firewall on the remote machine by running:

The telnet port is now allowed through the firewall.

Note: The command above is for the ufw firewall. If you are using a different firewall, follow the instructions for that specific program.

How to Use telnet in Linux

A vital prerequisite for using telnet is to have it installed on both the local and remote machine, and that the default port 23 is allowed through the firewall on the remote machine.

The syntax for the telnet command is:

telnet [options] [remote_server_address] [port]

The [options] and [port] parameters are optional. For [remote_server_address] , telnet accepts symbolic and numeric addresses.

Running the command without options or without specifying an address opens the telnet interactive mode:

Use the interactive shell to connect to remote servers, print the connection status, etc.

To end a session and exit telnet , run:

The sections below provide practical telnet use case examples.

Check for Open Ports

Although it is not a secure option for establishing a remote connection, telnet is a great way to check if a specific port is open on a server. Check if a certain port is answering any calls by specifying the port number in the command. Doing so allows you to see what’s going on in a network and if a port is responsive or not.

1. Use the following syntax:

telnet [server_address] [port]

2. Not specifying a port number defaults to port 23. For example, to check if port 22 is open on a server, run:

The connection breaks, which means that the specified port is not open.

3. However, trying port 80 yields a different result:

The output shows that the port is open since the connection was established.

Download Web Page to File

telnet allows users to connect to port 80 of a website and download the HTML source code to the terminal. This allows you to save and inspect the source code, check it for errors, etc.

1. For example, the following command connects to port 80 on google.com:

2. After establishing the connection, download the HTML web page by running:

The screenshot above shows that the command has downloaded the homepage source code.

3. Save the code to a file or inspect it in the terminal.

Test SMTP Communication

Another useful feature of telnet is that it allows users to test the SMTP port by sending emails directly from the command line. To do so, you need an email server that doesn’t require authentication. It is a great way to troubleshoot problems in an email client.

Note: Want to send and read email using the CLI? See how to use the Linux mail command.

Follow the steps below to send an email using telnet :

1. Connect to the server via the SMTP port:

telnet [server_address] [port]

For [server_address] , specify the SMTP server address. For example, for Gmail it is smtp.gmail.com, while the SMTP [port] can be 25, 465, 587, etc., depending on the provider.

Important: Since May 2022, Google has prohibited access to Google accounts for less secure apps and won’t accept connections from telnet .

2. Greet the server with HELO or EHLO :

5. Specify the subject and email body, separated by a blank line:

SUBJECT: This is the email subject. "" This is the email body.

Note: Most mail servers flag unsolicited anonymous mail, which means that it will likely end up in the spam folder.

Connect to Remote System

If you decide to use telnet for remote connections despite its lack of security, do it by specifying the remote machine’s IP address.

Make sure that telnet is installed on both machines and port 23 is allowed through the firewall on the remote machine.

When prompted, enter the account username and password to log in to the system. After logging in, you can operate the other machine remotely.

After the connection is established, you are in control of the remote machine.

This tutorial showed how to use the telnet command in Linux. Although it has poor security features and isn’t recommended for remote connections, the command has other uses that make it beneficial.

Next, see how SSH works and why it is more secure than telnet .

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