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9. Terminal Emulation; the Console

9.1 Terminal Emulation

Intro to Terminal Emulation

Since a PC has a screen and keyboard (as does a terminal) but also has much more computing power, it's easy to use some of this computing power to make the PC computer behave like a text terminal. This is one type of terminal emulation. Another type of terminal emulation is where you set up a real terminal to emulate another brand/model of terminal. To do this you select the emulation you want (called "personality" in Wyse jargon) from the terminal's set-up menu. This section is about the first type of emulation: emulating a terminal on a PC.

Emulation software is available for MS Windows and comes built-in with recent versions of MS Windows. Most Linux software can only emulate a VT100, VT102, or VT100/ANSI. If you find out about any others, let me know. Since most PC's have color monitors but VT100 and VT102 were designed for a monochrome monitor, the emulation usually adds color capabilities (and a choice of colors). Sometimes the emulation is not 100% perfect but this usually causes few problems. For using a Mac computer to emulate a terminal see the mini-howto: Mac-Terminal.

Don't Use TERM For Emulation

Some have erroneously thought that they could create an emulator at a Linux console (monitor) by setting the environment variable TERM to the type of terminal they would like to emulate. This does not work. The value of TERM only tells an application program what terminal you are using. This way it doesn't need to interactively ask you this question. If you're at the PC monitor it's a terminal of type "Linux" and your can't change this. So you must set TERM to "Linux".

If you set it to something else you are fibbing to application programs. As a result they will incorrectly interpret certain escape sequences from the console reulting in a corrupted interface. Since the Linux console behaves almost like a vt100 terminal, it could still work almost OK if you falsely claimed it was a vt100 (or some other terminal which is something like a vt100).

Communication (Dialing) programs

An emulation program is often combined with a modem dialing program (such as Minicom, Seyon, or Kermit) so that one may (for example) dial up public libraries to use their catalogs and indexes, (or even read magazine articles). Seyon is only for use with X-windows and can emulate Tektronix 4014 terminals. Emulators exist under DOS such as telix and procomm work just as well. The terminal emulated is often the old VT100, VT102, or ANSI (like VT100).

Emulation under X-Windows

Xterm (obsolete ??) may be run under X-Windows which can emulate a VT102, VT220, or Tektronix 4014. There is also an xterm emulation (although there is no real terminal named "xterm"). If you don't need the Tektronix 4014 emulation (a vector graphics terminal; see Graphics Terminals) you may use eterm. Predecessors to eterm are rxvt and xvt. eterm supports pixmaps.

For non-Latin alphabets, kterm is for Kanji terminal emulation (or for other non-Latin alphabets) while xcin is for Chinese. There is also 9term emulation. This seems to be more than just an emulator as it has a built-in editor and scroll-bars. It was designed for Plan 9, a Unix-like operating system from AT&T.

Real Terminals Better

Unless you are using X-Windows with a large display, a real terminal is often nicer to use than emulating one. It usually costs less, has better resolution for text, and has no disk drives to make annoying noises.

9.2 Testing Terminal Emulation

For the VT series terminals there is a test program: vttest to help determine if a terminal behaves correctly like a vt53, vt100, vt102, vt220, vt320, vt420 etc. There is no documentation but it has menus and is easy to use. To compile it run the configure script and then type "make". It may be downloaded from: ftp://ftp.clark/net:/pub/dickey/vttest/. An alternate download site is: http://sunsite.unc.edu/pub/Linux/utils/console/

9.3 The Linux Console

The console for a PC Linux system is the computer monitor It emulates a terminal of type "Linux". There is no way (unless you want to spend days rewriting the kernel code) to get it to emulate anything else. Setting the TERM environment variable to type of terminal other than "Linux" will not result in emulating that other terminal. It will only result in a corrupted interface since you have falsely declared (via the TERM variable) that your "terminal" is of a type different from what it is. See Don't Use TERM For Emulation

The "Linux" emulation is flexible and has features which go well beyond those of the vt102 terminal which it was intended to emulate. These include the ability to use custom fonts and easily re-map the keyboard (without patching the source code and recompiling the kernel as is required for the case of a real terminal). These extra features reside in the console driver software and not in the emulation software but the results are like it was part of the emulation.

Many commands exist (see Keyboard-and-Console-HOWTO) to utilize these added features. Real terminals, which use neither scan codes nor VGA cards, unfortunately can't use most of these features. One may recompile Linux to make a terminal receive the messages which normally go to the console. See Make a Terminal the Console.


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