Remember that Unix evolved in a time when many manufacturers made many different models of computer terminals, each with its own set of command codes for clearing the screen, moving the cursor to different screen positions, setting bold face, underline and other text characteristics, and so on. A typical Unix installation will be equipped to communicate with any of a few hundred different types of terminals.

Now, you're not using a terminal, but you are using a program that simulates one. telnet was originally intended to allow terminals to issue commands to remote CPUs, and ssh is intended as a replacement for the older telnet protocol, so your ssh client program actually works by simulating an “old-fashioned” computer terminal. The authors of your client program chose one or more kinds of terminal that they would simulate. For Unix to manipulate your screen appropriately, it most know what kind of terminal command codes your ssh client program is prepared to accept.

Find out the kind of terminal being emulated by your telnet program. You may need to consult the program documentation or help files for this. You may also be able to deduce this information from the program's “Options” or “Preferences” menus.

Here are some common choices:

SSH client program	TERM type	Comments
PuTTY	xterm
OpenSSH	xterm?	(Need to check this)
Command-line SSH, basic form, Linux or OS/X	xterm or linux
Command-line SSH, basic form, CygWin	xterm or rxvt	Depends on what type of window you type the command in.
Command-line SSH, xterm variant	xterm

Now, there is a protocol by which Unix systems can ask a terminal, “What kind are you?” , and the terminal responds with an identification code. Many simpler clients don't implement this feature, however, so you can't take it for granted.

Look at the messages that you received after after logging in. If it includes a line saying something like “Terminal type is…” and the terminal type that it names makes sense for your ssh client program, you're all set and you can skip the next step. But it there terminal type seems wrong, or you see a message indicating that you are on a “dumb terminal” 5

, you need to tell the Unix system what kind of terminal you are really emulating. The command to do so is where xxxx is the kind of terminal (e.g, setenv TERM vt100).

Some people also recommend that you follow this command with

which resets the terminal. In my own experience, this is usually unnecessary,and I have found that many communications programs don't deal well with this, but try it if your terminal seems to be misbehaving.

Most “dumb” terminals provide for 24 lines of text. Many telnet programs, however, allow more. If yours is one of these, you should tell Unix how many lines you are using by giving the command

where nn is the number of rows/lines.