Telnet

You use the telnet command to log in remotely to another system on your network. The system can be on your local area network or available through an Internet connection. Telnet operates as if you were logging into another system from a remote terminal. You will be asked for a login name and, in some cases, a password. In effect, you are logging into another account on another system. In fact, if you have an account on another system, you could use Telnet to log into it.

The original version of Telnet is noted for being very insecure. For secure connections over a network or the Internet, you should use the SSH or Kerberos versions of Telnet (see Chapter 18). They operate in the same way as the original but use authentication and encryption to secure the Telnet connection. Even so, it is advisable never to use Telnet to login to your root account.

You invoke the Telnet utility with the keyword telnet. If you know the name of the site you want to connect with, you can enter telnet and the name of the site on the Linux command line. As an alternative, you can use the K Desktop KTelnet utility. This provides a GUI interface to connecting and logging into remote systems.

$ telnet garnet.berkeley.edu
Connected to garnet
login:

The Telnet program also has a command mode with a series of commands you can use to configure your connection. You can enter the telnet command mode either by invoking Telnet with the keyword telnet or by pressing CTRL-] during a session. The Telnet help command lists all the Telnet commands you can use. A comprehensive list is available on the Man pages (man telnet). In the next example, the user first invokes the Telnet utility. A prompt is displayed next, indicating the command mode, telnet>. The Telnet command open then connects to another system.

$ telnet
telnet> open garnet.berkeley.edu
Connected to garnet.berkeley.edu
login:

Once connected, you follow the login procedure for that system. If you are logging into a regular system, you must provide a login name and password. Once logged in, you are provided with the operating system prompt; in the case of Linux or Unix, this will be either $ or %. You are then directly connected to an account on that system and can issue any commands you want. When you finish your work, you log out. This breaks the connection and returns you to the Telnet prompt on your own system. You can then quit Telnet with the quit command.

telnet> quit

When using Telnet to connect to a site that provides public access, you needn't provide a login name or password. Access is usually controlled by a series of menus that restrict what you can do on that system. If you are logging into a specific account on another system, you can use the -l option to specify the login name of that account.