13.5 telnet
Someone once stated that telnet(1) was the coolest thing he had ever seen on computers. The ability to remotely log in and do stuff on another computer is what separates Unix and Unix-like operating systems from other operating systems.
telnet allows you to log in to a computer, just as if you were sitting at the terminal. Once your username and password are verified, you are given a shell prompt. From here, you can do anything requiring a text console. Compose email, read newsgroups, move files around, and so on. If you are running X and you telnet to another machine, you can run X programs on the remote computer and display them on yours.
To login to a remote machine, use this syntax:
% telnet <hostname> |
If the host responds, you will receive a login prompt. Give it your username and password. That's it. You are now at a shell. To quit your telnet session, use either the exit command or the logout command.
 |
telnet does not encrypt the information it sends. Everything is sent in plain text, even passwords. It is not advisable to use telnet over the Internet. Instead, consider the Secure Shell. It encrypts all traffic and is available for free. |
13.5.1 The other use of telnet
Now that we have convinced you not to use the telnet protocol anymore to log into a remote machine, we'll show you a couple of useful ways to use telnet.
You can also use the telnet command to connect to a host on a certain port.
% telnet <hostname> [port] |
This can be quite handy when you quickly need to test a certain service, and you need full control over the commands, and you need to see what exactly is going on. You can interactively test or use an SMTP server, a POP3 server, an HTTP server, etc. this way.
In the next figure you'll see how you can telnet to a HTTP server on port 80, and get some basic information from it.
Figure 13-1. Telnetting to a webserver
% telnet store.slackware.com 80 Trying 69.50.233.153... Connected to store.slackware.com. Escape character is '^]'. HEAD / HTTP/1.0 HTTP/1.1 200 OK Date: Mon, 25 Apr 2005 20:47:01 GMT Server: Apache/1.3.33 (Unix) mod_ssl/2.8.22 OpenSSL/0.9.7d Last-Modified: Fri, 18 Apr 2003 10:58:54 GMT ETag: "193424-c0-3e9fda6e" Accept-Ranges: bytes Content-Length: 192 Connection: close Content-Type: text/html Connection closed by foreign host. % |
You can do the same for other plain-text protocols, as long as you know what port to connect to, and what the commands are.