540 lines
22 KiB
Plaintext
540 lines
22 KiB
Plaintext
<!-- This is an SGML document in the linuxdoc DTD describing
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hardwired terminals with FreeBSD. By Sean Kelly, (c) 1996.
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$Id: term.sgml,v 1.3 1996/10/04 22:54:17 wosch Exp $
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The FreeBSD Documentation Project
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<!DOCTYPE linuxdoc PUBLIC "-//FreeBSD//DTD linuxdoc//EN">
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<linuxdoc>
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<article>
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<title> Hardwired Terminals
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<author> Sean Kelly <tt/kelly@fsl.noaa.gov/
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<date> 24 June 1996, (c) 1996
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<abstract> This document describes using hardwired terminals
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attached to computers running FreeBSD. It describes how to
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set up the terminal hardware (including cabling), how to
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configure FreeBSD to provide login sessions to those
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terminals, and how to troubleshoot problems with terminals.
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</abstract>
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<toc>
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-->
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<sect><heading>Terminals<label id="term"></heading>
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<p><em>Contributed by &a.kelly;<newline>28 July 1996</em>
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Terminals provide a convenient and low-cost way to access the
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power of your FreeBSD system when you are not at the computer's
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console or on a connected network. This section describes how
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to use terminals with FreeBSD.
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<sect1><heading>Uses and Types of Terminals<label
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id="term:uses"></heading>
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<p>The original Unix systems did not have consoles. Instead,
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people logged in and ran programs through terminals that were
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connected to the computer's serial ports. It is quite similar
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to using a modem and some terminal software to dial into a
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remote system to do text-only work.
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Today's PCs have consoles capable of high quality graphics,
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but the ability to establish a login session on a serial port
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still exists in nearly every Unix-style operating system
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today; FreeBSD is no exception. By using a terminal attached
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to a unused serial port, you can log in and run any text
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program that you would normally run on the console or in an
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<tt/xterm/ window in the X Window System.
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For the business user, you can attach many terminals to a
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FreeBSD system and place them on your employees' desktops.
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For a home user, a spare computer such as an older IBM PC or a
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Macintosh can be a terminal wired into a more powerful
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computer running FreeBSD. You can turn what might otherwise
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be a single-user computer into a powerful multiple user
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system.
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For FreeBSD, there are three kinds of terminals:
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<itemize>
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<item><ref name="Dumb terminals" id="term:dumb">
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<item><ref name="PCs acting as terminals" id="term:pcs">
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<item><ref name="X terminals" id="term:x">
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</itemize>
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The remaining subsections describe each kind.
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<sect2><heading>Dumb Terminals<label id="term:dumb"></heading>
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<p>Dumb terminals are specialized pieces of hardware that let
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you connect to computers over serial lines. They are called
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``dumb'' because they have only enough computational power
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to display, send, and receive text. You cannot run any
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programs on them. It is the computer to which you connect
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them that has all the power to run text editors, compilers,
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email, games, and so forth.
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There are hundreds of kinds of dumb terminals made by
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many manufacturers, including Digital Equipment
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Corporation's VT-100 and Wyse's WY-75. Just about any kind
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will work with FreeBSD. Some high-end terminals can even
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display graphics, but only certain software packages can
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take advantage of these advanced features.
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Dumb terminals are popular in work environments where
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workers do not need access to graphic applications such as
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those provided by the X Window System.
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<sect2><heading>PCs Acting As Terminals<label
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id="term:pcs"></heading>
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<p>If a <ref name="dumb terminal" id="term:dumb"> has just
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enough ability to display, send, and receive text, then
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certainly any spare personal computer can be a dumb
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terminal. All you need is the proper cable and some
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<em/terminal emulation/ software to run on the computer.
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Such a configuration is popular in homes. For example, if
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your spouse is busy working on your FreeBSD system's
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console, you can do some text-only work at the same time
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from a less powerful personal computer hooked up as a
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terminal to the FreeBSD system.
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<sect2><heading>X Terminals<label id="term:x"></heading>
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<p>X terminals are the most sophisticated kind of terminal
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available. Instead of connecting to a serial port, they
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usually connect to a network like Ethernet. Instead of
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being relegated to text-only applications, they can display
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any X application.
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We introduce X terminals just for the sake of completeness.
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However, this chapter does <em/not/ cover setup,
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configuration, or use of X terminals.
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<sect1><heading>Cables and Ports<label
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id="term:cables-ports"></heading>
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<p>To connect a terminal to your FreeBSD system, you need the
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right kind of cable and a serial port to which to connect it.
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This section tells you what to do. If you are already
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familiar with your terminal and the cable it requires, skip to
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<ref name="Configuration" id="term:config">.
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<sect2><heading>Cables<label id="term:cables"></heading>
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<p>Because terminals use serial ports, you need to use
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serial---also known as RS-232C---cables to connect the
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terminal to the FreeBSD system.
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There are a couple of kinds of serial cables. Which one
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you'll use depends on the terminal you want to connect:
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<itemize>
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<item>If you are connecting a personal computer to act as
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a terminal, use a <ref name="null-modem" id="term:null">
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cable. A null-modem cable connects two computers or
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terminals together.
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<item>If you have an actual terminal, your best source of
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information on what cable to use is the documentation
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that accompanied the terminal. If you do not have the
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documentation, then try a <ref name="null-modem"
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id="term:null"> cable. If that does not work, then try
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a <ref name="standard" id="term:std"> cable.
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</itemize>
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Also, the serial port on <em/both/ the terminal and your
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FreeBSD system must have connectors that will fit the cable
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you are using.
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<sect3><heading>Null-modem cables<label id="term:null"></heading>
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<p>A null-modem cable passes some signals straight through,
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like ``signal ground,'' but switches other signals. For
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example, the ``send data'' pin on one end goes to the
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``receive data'' pin on the other end.
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If you like making your own cables, here is a table
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showing a recommended way to construct a null-modem cable
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for use with terminals. This table shows the RS-232C
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signal names and the pin numbers on a DB-25 connector.
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<tscreen><verb>
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Signal Pin# Pin# Signal
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TxD 2 ----------------------- 3 RxD
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RxD 3 ----------------------- 2 TxD
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DTR 20 ----------------------- 6 DSR
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DSR 6 ----------------------- 20 DTR
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SG 7 ----------------------- 7 SG
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DCD 8 ----------------------+ 4 RTS*
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*RTS 4 + + 5 CTS*
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*CTS 5 +---------------------- 8 DCD
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* Connect pins 4 to 5 internally in the connector hood, and then to
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pin 8 in the remote hood.
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</verb></tscreen>
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<sect3><heading>Standard RS-232C Cables<label
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id="term:std"></heading>
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<p>A standard serial cable passes all the RS-232C signals
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straight-through. That is, the ``send data'' pin on one
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end of the cable goes to the ``send data'' pin on the
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other end. This is the type of cable to connect a modem
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to your FreeBSD system, and the type of cable needed for
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some terminals.
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<sect2><heading>Ports<label id="term:ports"></heading>
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<p>Serial ports are the devices through which data is
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transferred between the FreeBSD host computer and the
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terminal. This section describes the kinds of ports that
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exist and how they are addressed in FreeBSD.
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<sect3><heading>Kinds of Ports<label
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id="term:portkinds"></heading>
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<p>Several kinds of serial ports exist. Before you purchase
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or construct a cable, you need to make sure it will fit
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the ports on your terminal and on the FreeBSD system.
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Most terminals will have DB25 ports. Personal computers,
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including PCs running FreeBSD, will have DB25 or DB9
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ports. If you have a multiport serial card for your PC,
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you may have RJ-12 or RJ-45 ports.
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See the documentation that accompanied the hardware for
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specifications on the kind of port in use. A visual
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inspection of the port often works, too.
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<sect3><heading>Port Names<label
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id="term:portnames"></heading>
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<p>In FreeBSD, you access each serial port through an entry
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in the <tt>/dev</tt> directory. There are two different
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kinds of entries:
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<itemize>
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<item>Callin ports are named <tt>/dev/ttyd<it/X/</tt>
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where <it/X/ is the port number, starting from zero.
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Generally, you use the callin port for terminals.
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Callin ports require that the serial line assert the
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data carrier detect (DCD) signal to work.
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<item>Callout ports are named <tt>/dev/cuaa<it/X/</tt>.
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You usually do not use the callout port for terminals,
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just for modems. You may use the callout port if the
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serial cable or the terminal does not support the
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carrier detect signal.
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</itemize>
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See the sio(4) manual page for more information.
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If you have connected a terminal to the first serial port
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(COM1 in DOS parlance), then you want to use
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<tt>/dev/ttyd0</tt> to refer to the terminal. If it is on
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the second serial port (also known as COM2), it is
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<tt>/dev/ttyd1</tt>, and so forth.
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Note that you may have to configure your kernel to support
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each serial port, especially if you have a multiport
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serial card. See <ref name="Configuring the FreeBSD
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Kernel" id="kernelconfig"> for more information.
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<sect1><heading>Configuration<label id="term:config"></heading>
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<p>This section describes what you need to configure on your
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FreeBSD system to enable a login session on a terminal. It
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assumes you have already configured your kernel to support the
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serial port to which the terminal is connected---and that you
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have connected it.
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In a nutshell, you need to tell the <tt/init/ process, which is
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responsible for process control and initialization, to start a
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<tt/getty/ process, which is responsible for reading a login
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name and starting the <tt/login/ program.
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To do so, you have to edit the <tt>/etc/ttys</tt> file.
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First, use the <tt/su/ command to become root. Then, make the
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following changes to <tt>/etc/ttys</tt>:
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<enum>
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<item>Add an line to <tt>/etc/ttys</tt> for the entry in the
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<tt>/dev</tt> directory for the serial port if it is not
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already there.
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<item>Specify that <tt>/usr/libexec/getty</tt> be run on the
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port, and specify the appropriate <tt/getty/ type from the
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<tt>/etc/gettytab</tt> file.
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<item>Specify the default terminal type.
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<item>Set the port to ``on.''
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<item>Specify whether the port should be ``secure.''
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<item>Force <tt/init/ to reread the <tt>/etc/ttys</tt> file.
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</enum>
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As an optional step, you may wish to create a custom
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<tt/getty/ type for use in step 2 by making an entry in
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<tt>/etc/gettytab</tt>. This document does not explain how to
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do so; you are encouraged to see the gettytab(5) and the
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getty(8) manual pages for more information.
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The remaining sections detail how to do these steps. We will
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use a running example throughout these sections to illustrate
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what we need to do. In our example, we will connect two
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terminals to the system: a Wyse-50 and a old 286 IBM PC
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running Procomm terminal software emulating a VT-100 terminal.
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We connect the Wyse to the second serial port and the 286 to
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the sixth serial port (a port on a multiport serial card).
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For more information on the <tt>/etc/ttys</tt> file, see the
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ttys(5) manual page.
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<sect2><heading>Adding an Entry to <tt>/etc/ttys</tt><label
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id="term:etcttys"></heading>
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<p>First, you need to add an entry to the <tt>/etc/ttys</tt>
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file, unless one is already there.
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The <tt>/etc/ttys</tt> file lists all of the ports on your
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FreeBSD system where you want to allow logins. For example,
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the first virtual console <tt>ttyv0</tt> has an entry in
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this file. You can log in on the console using this entry.
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This file contains entries for the other virtual consoles,
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serial ports, and pseudo-ttys. For a hardwired terminal,
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just list the serial port's <tt>/dev</tt> entry without the
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<tt>/dev</tt> part.
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When you installed your FreeBSD system, the
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<tt>/etc/ttys</tt> file included entries for the first four
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serial ports: <tt/ttyd0/ through <tt/ttyd3/. If you are
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attaching a terminal on one of those ports, you do not need
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to add an entry.
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In our example, we attached a Wyse-50 to the second serial
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port, <tt/ttyd1/, which is already in the file. We need to
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add an entry for the 286 PC connected to the sixth serial
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port. Here is an excerpt of the <tt>/etc/ttys</tt> file
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after we add the new entry:
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<tscreen><verb>
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ttyd1 "/usr/libexec/getty std.9600" unknown off secure
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ttyd5
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</verb></tscreen>
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<sect2><heading>Specifying the <tt/getty/ Type<label
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id="term:getty"></heading>
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<p>Next, we need to specify what program will be run to handle
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the logins on a terminal. For FreeBSD, the standard program
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to do that is <tt>/usr/libexec/getty</tt>. It is what
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provides the <tt>login:</tt> prompt.
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The program <tt/getty/ takes one (optional) parameter on its
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command line, the <em/<tt/getty/ type/. A <tt/getty/ type
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tells about characteristics on the terminal line, like bps
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rate and parity. The <tt/getty/ program reads these
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characteristics from the file <tt>/etc/gettytab</tt>.
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The file <tt>/etc/gettytab</tt> contains lots of entries for
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terminal lines both old and new. In almost all cases, the
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entries that start with the text <tt/std/ will work for
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hardwired terminals. These entries ignore parity. There is
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a <tt/std/ entry for each bps rate from 110 to 115200. Of
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course, you can add your own entries to this file. The
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manual page gettytab(5) provides more information.
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When setting the <tt/getty/ type in the <tt>/etc/ttys</tt>
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file, make sure that the communications settings on the
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terminal match.
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For our example, the Wyse-50 uses no parity and connects at
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38400 bps. The 286 PC uses no parity and connects at 19200
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bps. Here is the <tt>/etc/ttys</tt> file so far (showing
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just the two terminals in which we are interested):
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<tscreen><verb>
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ttyd1 "/usr/libexec/getty std.38400" unknown off secure
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ttyd5 "/usr/libexec/getty std.19200"
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</verb></tscreen>
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Note that the second field---where we specify what program
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to run---appears in quotes. This is important, otherwise
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the type argument to <tt/getty/ might be interpreted as the
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next field.
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<sect2><heading>Specifying the Default Terminal Type<label
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id="term:deftermtype"></heading>
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<p>The third field in the <tt>/etc/ttys</tt> file lists the
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default terminal type for the port. For dialup ports, you
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typically put <tt/unknown/ or <tt/dialup/ in this field
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because users may dial up with practically any kind of
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terminal or software. For hardwired terminals, the terminal
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type does not change, so you can put a real terminal type in
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this field.
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Users will usually use the <tt/tset/ program in their
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<tt/.login/ or <tt/.profile/ files to check the terminal
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type and prompt for one if necessary. By setting a terminal
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type in the <tt>/etc/ttys</tt> file, users can forego such
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prompting.
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To find out what terminal types FreeBSD supports, see the
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file <tt>/usr/share/misc/termcap</tt>. It lists about 600
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terminal types. You can add more if you wish. See the
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termcap(5) manual page for information.
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In our example, the Wyse-50 is a Wyse-50 type of terminal
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(although it can emulate others, we will leave it in Wyse-50
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mode). The 286 PC is running Procomm which will be set to
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emulate a VT-100. Here are the pertinent yet unfinished
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entries from the <tt>/etc/ttys</tt> file:
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<tscreen><verb>
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ttyd1 "/usr/libexec/getty std.38400" wy50 off secure
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ttyd5 "/usr/libexec/getty std.19200" vt100
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</verb></tscreen>
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<sect2><heading>Enabling the Port<label
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id="term:enable"></heading>
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<p>The next field in <tt>/etc/ttys</tt>, the fourth field,
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tells whether to enable the port. Putting <tt/on/ here will
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have the <tt/init/ process start the program in the second
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field, <tt/getty/, which will prompt for a login. If you
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put <tt/off/ in the fourth field, there will be no
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<tt/getty/, and hence no logins on the port.
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So, naturally, you want an <tt/on/ in this field. Here
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again is the <tt>/etc/ttys</tt> file. We have turned each
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port <tt/on/.
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<tscreen><verb>
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ttyd1 "/usr/libexec/getty std.38400" wy50 on secure
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ttyd5 "/usr/libexec/getty std.19200" vt100 on
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</verb></tscreen>
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<sect2><heading>Specifying Secure Ports<label
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id="term:secure"></heading>
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<p>We have arrived at the last field (well, almost: there is
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an optional <tt/window/ specifier, but we will ignore that).
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The last field tells whether the port is secure.
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What does ``secure'' mean?
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It means that the root account (or any account with a user
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ID of 0) may login on the port. Insecure ports do not
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allow root to login.
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How do you use secure and insecure ports?
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By marking a port as insecure, the terminal to which it is
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connected will not allow root to login. People who know
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the root password to your FreeBSD system will first have to
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login using a regular user account. To gain superuser
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privileges, they will then have to use the <tt/su/ command.
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Because of this, you will have two records to help track
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down possible compromises of root privileges: both the login
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and the <tt/su/ command make records in the system log (and
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logins are also recorded in the <tt/wtmp/ file).
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By marking a port as secure, the terminal will allow root
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in. People who know the root password will just login as
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root. You will not have the potentially useful login and
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<tt/su/ command records.
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Which should you use?
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Just use ``insecure.'' Use ``insecure'' <em/even/ for
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terminals <em/not/ in public user areas or behind locked
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doors. It is quite easy to login and use <tt/su/ if you
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need superuser privileges.
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Here finally are the completed entries in the
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<tt>/etc/ttys</tt> file, with comments added to describe
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where the terminals are:
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<tscreen><verb>
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ttyd1 "/usr/libexec/getty std.38400" wy50 on insecure # Kitchen
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ttyd5 "/usr/libexec/getty std.19200" vt100 on insecure # Guest bathroom
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</verb></tscreen>
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<sect2><heading>Force <tt/init/ to Reread
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<tt>/etc/ttys</tt><label id="term:hup"></heading>
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<p>When you boot FreeBSD, the first process, <tt/init/, will
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read the <tt>/etc/ttys</tt> file and start the programs
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listed for each enabled port to prompt for logins.
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After you edit <tt>/etc/ttys</tt>, you do not want to have
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to reboot your system to get <tt/init/ to see the changes.
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So, <tt/init/ will reread <tt>/etc/ttys</tt> if it receives
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a SIGHUP (hangup) signal.
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So, after you have saved your changes to <tt>/etc/ttys</tt>,
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|
send SIGHUP to <tt/init/ by typing:
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|
<tscreen><verb>
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|
kill -HUP 1
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|
</verb></tscreen>
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|
(The <tt/init/ process <em/always/ has process ID 1.)
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|
If everything is set up correctly, all cables are in place,
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|
and the terminals are powered up, you should see login
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|
prompts. Your terminals are ready for their first logins!
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|
|
|
<sect1><heading>Debugging your connection<label
|
|
id="term:debug"></heading>
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|
<p>Even with the most meticulous attention to detail, something
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|
could still go wrong while setting up a terminal. Here is a
|
|
list of symptoms and some suggested fixes.
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|
|
|
<descrip>
|
|
<tag/No login prompt appears/
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|
|
|
Make sure the terminal is plugged in and powered up. If
|
|
it is a personal computer acting as a terminal, make sure
|
|
it is running terminal emulation software on the correct
|
|
serial port.
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|
|
|
Make sure the cable is connected firmly to both the
|
|
terminal and the FreeBSD computer. Make sure it is the
|
|
right kind of cable.
|
|
|
|
Make sure the terminal and FreeBSD agree on the bps rate
|
|
and parity settings. If you have a video display
|
|
terminal, make sure the contrast and brightness controls
|
|
are turned up. If it is a printing terminal, make sure
|
|
paper and ink are in good supply.
|
|
|
|
Make sure that a <tt/getty/ process is running and serving
|
|
the terminal. Type
|
|
<tscreen><verb>
|
|
ps -axww|grep getty
|
|
</verb></tscreen>
|
|
to get a list of running <tt/getty/ processes. You should
|
|
see an entry for the terminal. For example, the display
|
|
<tscreen><verb>
|
|
22189 d1 Is+ 0:00.03 /usr/libexec/getty std.38400 ttyd1
|
|
</verb></tscreen>
|
|
shows that a <tt/getty/ is running on the second serial
|
|
port <tt/ttyd1/ and is using the <tt/std.38400/ entry in
|
|
<tt>/etc/gettytab</tt>.
|
|
|
|
If no <tt/getty/ process is running, make sure you have
|
|
enabled the port in <tt>/etc/ttys</tt>. Make sure you
|
|
have run <tt/kill -HUP 1/.
|
|
|
|
<tag/Garbage appears instead of a login prompt/
|
|
|
|
Make sure the terminal and FreeBSD agree on the bps rate
|
|
and parity settings. Check the getty processes to make
|
|
sure the correct <tt/getty/ type is in use. If not, edit
|
|
<tt>/etc/ttys</tt> and run <tt/kill -HUP 1/.
|
|
|
|
<tag/Characters appear doubled; the password appears when typed/
|
|
|
|
Switch the terminal (or the terminal emulation software)
|
|
from ``half duplex'' or ``local echo'' to ``full duplex.''
|
|
|
|
</descrip>
|
|
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