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Linux Pocket Guide, 2nd Edition by Daniel J. Barrett

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Name

telnet — stdin  stdout  - file  -- opt  --help  --version

Synopsis

telnet [options] host [port]

The telnet program logs you into a remote machine where you already have an account.

$ telnet remote.example.com

Avoid telnet for remote logins: most implementations are insecure and send your password over the network in plain text for anyone to steal. Use ssh instead, which protects your password and data via encryption. There are two exceptions:

  • In a Kerberos environment, using enhanced (“kerberized”) telnet software on both the client and server side. See http://web.mit.edu/kerberos/ for more information.

  • Connecting to a remote port when you aren’t sending any sensitive information at all. For example, to check for the presence of a web server (port 80) on a remote system:

    $ telnet remote.example.com 80
    Trying 192.168.55.21...
    Connected to remote.example.com (192.168.55.21).
    Escape character is '^]'.
    xxx               Type some junk and press Enter
    <HTML><HEAD>      Yep, it’s a web server
    <TITLE>400 Bad Request</TITLE>
    </HEAD><BODY>
    <H1>Bad Request</H1>
    Your browser sent a request that
    this server could not understand.<P>
    </BODY></HTML>
    Connection closed by foreign host.

To discourage you further from using telnet, we aren’t even going to describe its options.

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