telnet Command: Tutorial & Examples

Connect to a remote host using the Telnet protocol

The telnet command is used to connect to a remote host using the Telnet protocol, which is a plaintext protocol used to establish a connection and communicate with a remote server. Telnet is commonly used to test network connectivity and to check the status of various services running on a server.

The basic syntax for using the telnet command is as follows:

telnet [hostname or IP] [port]

Here are a few examples of how the telnet command can be used to check different ports on a remote host:

Check if a remote HTTP server is running on port 80:

telnet example.com 80

Check if a remote SSH server is running on port 22:

telnet example.com 22

Check if a remote SMTP server is running on port 25:

telnet example.com 25

In the first example, the telnet command is used to connect to the remote host example.com on port 80, which is the default port for the HTTP protocol. In the second example, the telnet command is used to connect to the remote host on port 22, which is the default port for the SSH protocol. In the third example, the telnet command is used to connect to the remote host on port 25, which is the default port for the SMTP protocol.

When you run telnet command to a port, if the connection is successful, you will see a message like Connected to [hostname] and you will see a cursor blinking. If the port is closed or not available the command will return with an error message such as Could not open connection to the host, on port [port]: Connect failed.

It's worth noting that telnet is an insecure protocol since it sends data in plaintext, and it's recommended to use SSH protocol to connect to remote servers. Also, Telnet support is not enabled by default on many modern Linux distributions, so you may need to install it before using it.