telnet

Connect to a host on default port (23)

$ telnet [host]

$ telnet [host] [port]

$ telnet [host] [80]

$ telnet -a [host]

$ telnet -l [username] [host]

$ telnet -e [^X] [host]

$ telnet -4 [host]

telnet [options] [host] [port]

telnet is a user interface to the TELNET protocol for communicating with remote hosts. It can connect to any TCP port, making it useful for testing network services beyond traditional terminal access.
Without arguments, telnet enters command mode with a telnet> prompt. With a host argument, it attempts to connect immediately. The escape character (default Ctrl+]) returns to command mode during a connection.
Common uses include testing web servers (port 80), mail servers (port 25), and verifying if network services are accessible. The protocol transmits data in plaintext without encryption.

-4

Force IPv4 address resolution

Force IPv6 address resolution

Request 8-bit data path

Attempt automatic login with current username

Specify username for automatic login

Set escape character (default: ^])

Disable escape character

Enable debug mode

Record trace information to file

Disable automatic login

Use 8-bit data path on output only

Strip 8th bit on input and output

When in telnet command mode (press escape character):
open host [port]

Connect to a host

Close current connection

Exit telnet

Show connection status

Send special characters

Set telnet variable

Toggle option on/off

Show help

Telnet transmits all data including passwords in plaintext—never use it for sensitive connections over untrusted networks. Use SSH instead for secure remote access. Telnet may not be installed by default on modern systems. Some firewalls block the default telnet port (23). The protocol is considered obsolete for remote administration.

The TELNET protocol was developed in 1969 as one of the earliest internet protocols, defined in RFC 15 and later RFC 854. It provided remote terminal access over ARPANET, the precursor to the internet. Telnet was the standard for remote Unix access until the mid-1990s when SSH emerged as a secure replacement. While deprecated for remote login, telnet remains useful for testing and debugging network services.

ssh(1), nc(1), netcat(1), rlogin(1)