BURKS 2/BURKS_AUG97.ISO/BURKS/LINUX/HOWTO/mini/xterm.txt

Text File | 1997-07-07 | 29KB | 638 lines

The X Terminal HOWTO

How to connect an X terminal to a Linux PC
Version 1.0 BETA (July 1995)
Scot W. Stevenson <[e-mail]>


    This document gives a brief introduction to how to connect an X terminal
    to a Linux PC. It assumes a basic knowledge of the X Window System,
    TCP/IP addressing, and ethernet cards.


1.0 Introduction

    This is the first version of the document and should be considered BETA.
    It is more of a been-there, done-that text than a comprehensive treatment.
    Discussions of access control mechanisms (e.g. xaccess, xhost,
    MIT-COOKIEs), and the use of NFS, are not yet included.

    Most X terminals now have a whole host of advanced features which allow
    them to be more than mere X servers. For the most part, these features
    will be ignored.


1.1 Changes from previous versions

    (There are no previous versions, so everything was changed)


1.2 Disclaimers

    Neither the author nor the distributors of this HOWTO are in any way
    responsible for physical, financial, or moral damage incurred by
    following the suggestions in this text. In short: "Yea though I talk...."


1.3 Copyright

    The Linux Xterminal HOWTO is copyrighted (C) 1995 by Scot W. Stevenson.
    Linux HOWTO documents may be reproduced and distributed in whole or in
    part, in any medium physical or electronic, as long as this copyright
    notice is retained on all copies. Commercial redistribution is allowed
    and encouraged. The author, however, would like to be notified of any
    such distributions.

    All translations, derivative works, or aggregate works incorporating
    any Linux HOWTO documents must be covered under this copyright notice.
    In othe words, you may not produce a derivative work from a HOWTO and
    impose additional restrictions on its distribution. Exceptions to these
    rules may be granted under certain conditions.

    In short, we wish to promote dissemination of this information through
    as many channels as possible. However, we do wish to retain copyright
    on the HOWTO documents, and would like to be notified of any plans to
    redistribute the HOWTOs.

    Should you have any questions, please contact Greg Hankins, the Linux
    HOWTO coordinator, at [e-mail]. You may finger his address
    for phone number and additional contact information.


1.3 New Versions and Feedback

    New versions of this document can be found on sunsite.unc.edu in
    the /pub/Linux/docs/HOWTO/ directory. If you do not have FTP
    access, you can try to get Linux Help Files via Bill Riemers. Send
    email to [e-mail] with a subject of "help" for more
    infomation and an index file.

    Any additions to, corrections of, or comments about this document would
    be most welcomed! Please send email to

                 [e-mail] (Scot W. Stevenson)

    I would especially like to hear from you if you already have experience
    with linking an X terminal to a Linux machine, even if is only something
    like "worked on this machine with this terminal."

    On the board for the next versions are access control mechanisms and
    the use of NFS filesystems for booting.


2.0 Background

    This section provides some very basic information for those not familiar
    with the X Window System and its terminal-ology. If you have at least
    some experience with X and X terminals, you should be able to skip
    this part with no ill effects.


2.1 What is X?

    The X Window System, or just X (never X Windows), is "a portable,
    network-transparent window system" as the man page has it. It provides
    a graphic environment that cuts across operating systems, vendors, and
    hardware types. When people talk about a window system in connection with
    Unix, they almost always mean X.

    The most important characteristic of X in our case is the strict
    division between the programs that control the local hardware that the
    user interfaces with (screen, keyboard, mouse, etc.), and those programs
    the user actually wants to run (editor, spreadsheet, DOOM). This means
    that the interface software, which is called the X server, can be
    on a one machine, while the actual programs, or X clients, can be on
    one or even more than one machine at a totally different location.
    Note that the terms "server" and "client" are used in the reverse sense
    of what they usually are.

    Linux comes with a collection of X servers from the XFree86 project,
    that is, servers for SVGA Video cards, as well as a whole host of X
    clients such as xv, maze, and xterm. If you are new to X, you might
    want to get some hands-on experience with X on the Linux machine before
    attempting to link up an X terminal.


2.2 What is an X terminal?

    An X terminal (referred to as XT from now on) is a specialized piece of
    hard- and software which combine into an X server, that is, the part of
    X that manages in- and output to and from the user. In the most
    primitive case, only the X server program and communcication software are
    included. Even the window manager comes from the host computer, to which
    the XT is connected by ethernet (or in rare cases serial lines), using
    TCP/IP.

    The hardware of an XT will include at least a (large) screen, keyboard,
    mouse, some RAM, and jacks for ethernet cables. Most XTs do not have a
    hard disk, a floppy drive, or other such means of data transfer.
    This means that the XT either has its operating system in ROM (rare),
    or gets it from a host on the net that it is attached to.

    To get to its operating system from the Linux computer at boot time,
    the XT usually does something like this: It sends out a cry of help
    through the net with its ethernet number as a name tag. A "real" computer
    on the net compares this number with a list of them, and if a match
    is found, sends the XT the IP number it has been assigned to (via the
    bootpd daemon). This allows the XT to download its operating system and
    other data it needs from the hard disk of the host computer (usually via
    tftp). This is the procedure explained here in detail.

    An XT is therefore actually a full-fledged computer, with its own IP
    number, RAM, program, and independent hardware, albeit more like
    an idiot savant. It's great at what it does best, managing X graphics,
    but not much good for anything else.


2.3 Advantages and Disadvantages

    Ideally, an XT is silent, swift, and deadly. Usually without fan, floppy
    or hard disk, they make no noise at all, and with a few meters of
    ethernet cable you can put your loudish computer in a different room and
    have the silent XT on your desk. Since the XT is built for X and graphics,
    it is faster than, say, an X server program unter MS Windows or DOS.

    With the server on one machine and the client on another, the processor
    doesn't have to handle both at once. Though this might not be noticable
    in terms of speed (since the data now has to be moved over the ethernet),
    it will reduce the CPU load and save memory on the Linux machine that
    would otherwise be swallowed by the X server.

    On the flip side, you will need an ethernet card, which usually means
    giving up a slot and an IRQ. Depending on the manufacturer, the software
    for the XT can take up around 20 MBytes of hard disk space on your Linux
    machine. You can almost always delete a lot of unused stuff once you
    figure out what is really needed. Most XTs will require the host machine
    to have the bootpd and tftpd daemons installed and running - both are
    potential security holes. You will probably want to have a further daemon,
    xdm, running in the background. And yes, that big XT screen will take up
    a lot of desk space.


2.4 What do I need?

    Kind of you to ask! But more appropriately, what do you need?

    First of all, you need an XT. If you have lots of money, and we do mean
    lots, you can go out and buy one. Jim Morton <jim@a