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<TITLE>The Answer Guy 29: Connecting a Dumb Terminal to your Linux
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<!--endcut ========================================================= -->
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<H4>"Linux Gazette...<I>making Linux just a little more fun!</I>"
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</H4>
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<P> <hr> <P>
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<!-- =============================================================== -->
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<H1 align="center"><A NAME="answer">
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<img src="../gx/dennis/qbubble.gif" alt="" border="0" align="middle">
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<a href="./index.html">The Answer Guy</a>
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<img src="../gx/dennis/bbubble.gif" alt="" border="0" align="middle">
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</A></H1> <BR>
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<H4 align="center">By James T. Dennis,
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<a href="mailto:linux-questions-only@ssc.com">linux-questions-only@ssc.com</a><BR>
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Starshine Technical Services,
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<A HREF="http://www.starshine.org/">http://www.starshine.org/</A> </H4>
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<p><hr><p>
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<H3><img src="../gx/dennis/qbub.gif" alt="(?)" width="50" height="28"
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align="left" border="0">
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Connecting a Dumb Terminal to your Linux System
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</H3>
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<p><strong>From Mark Cohen on 07 May 1998
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<br><br>
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Jim,
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<br><br>
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My name is Mark, I met you at the
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<a href="http://www.balug.org/">balug</a> meeting this week. I
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just wanted to shoot off a note to you about getting <tt>getty</tt> to
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work on my linux box (RH5.0) Im trying to connect my dumb terminal to
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it (pilot)
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<br><br>
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Any help would be greatly appreciated!
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<br><br>
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-Mark
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</strong></p>
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<blockquote><img src="../gx/dennis/bbub.gif" width="50" height="28" alt="(!)"
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align="left" border="0">
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The simplest method that I know of is to add a line like
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this to your <tt>/etc/inittab</tt> file:
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<pre>
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t1:23:respawn:/sbin/agetty -L 38400,19200,9600,2400,1200 ttyS1 vt100
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</pre>
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... assuming you have '<tt>agetty</tt>', that you want to use a null
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modem on COM2 (use ttyS0 for COM1 etc), and that your
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communications package on the PalmPilot will do vt100
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emulation).
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<br><br>
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If you don't have a copy of '<tt>agetty</tt>' you can use a line
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like:
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<pre>
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t1:2345:respawn:/sbin/getty ttyS2 DT38400 vt100
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</pre>
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... assuming you have a reasonable <tt>/etc/gettydefs</tt> (like
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the default one that used to come with Red Hat 4.x --- and
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is probably unchanged in newer releases). I won't go into
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the details about how the gettydefs file is constructed,
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let's suffice it to say that the syntax was "baroque".
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<br><br>
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It's undoubtedly possible to use <tt>uugetty</tt> and
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<tt>getty_ps</tt> with these as well --- though I haven't ever
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bothered with those packages. It should also be possible to use
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<tt>mgetty</tt> (which I use for modem dial-in lines and incoming
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fax support). However that doesn't seem to work even when I use
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the <tt>-r</tt> switch as specified in the manual.
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<br><br>
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Definitely don't try this with <tt>mingetty</tt> --- that is designed
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purely for use with virtual consoles.
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<br><br>
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In any event, these examples use "<tt>t1</tt>" as the inittab
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entry "id" and I have them enabled at different runlevels
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(since these examples are from different machines on my
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network). Read the <tt>inittab(5)</tt> man page for details about
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what the fields mean.
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<br><br>
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After you've edited this file simply issue the command:
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<br><br>
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'<tt>telinit q</tt>'
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<br><br>
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... to "tell init" to re-read it's configuration file and
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implement your changes. In a few seconds you should be
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able to login on that line (you might have to hit [Enter]
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a couple of times to get a login prompt).
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<br><br>
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If you don't get a login prompt, or you see a console message
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like: "<tt>respawning too fast.... disabled for five minutes</tt>"
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(check your <tt>/var/log/messages</tt> file for this and similar
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errors from init and/or from any '<tt>getty</tt>' that you happen
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to be using), you should double-check the syntax of your entry,
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double-check which serial port you're plugged into (remember Linux'
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numbering of serial and printer ports sometimes doesn't correspond to
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DOS/BIOS extensions --- some crufty hardware may cause confusion),
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and check for IRQ conflicts and cabling errors.
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<br><br>
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If you still have problems with it after you've double and
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triple checked every detail than you have some troubleshooting
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choices:
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<ul>
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<li>buy a cheap "breakout" box and watch how the
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LED's respond to your software activity.
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<li>connect another system, even a DOS laptop and
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run <a href="http://www.columbia.edu/kermit/">C-Kermit</a>
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or <a href="http://delta.com/">Telix</a> or
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whatever you like in "host mode" and try to access that
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port from the other direction.
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<li>connect a normal external modem to the box and
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see if you can connect and so simple AT commands
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to it.
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</ul>
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In any of these cases you can play with a wide variety of
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'<tt>setserial</tt>' and '<tt>stty</tt>' commands to try and get
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the serial port to respond and/or behave properly. Before you spend
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too long with those, however, I have to say that the times
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when I've resorted to them as part of my troubleshooting
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have consistently been fixed by untangling an IRQ conflict
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or replacing a bad serial port (usually a whole multi-function
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controller, actually).
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<br><br>
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I personally have given up on the cheap $15 IDE/floppy/serial
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cards and I pay a bit extra for the
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<a href="http://www.quickpath.com/">QuickPath</a> "FlexPort"
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cards (which usually come in at close to $100 US). Serial
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ports are hard enough to deal with without having flaky
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hardware underneath it. (Luckily most of the modern
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motherboard that have built-in serial ports have stopped
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putting in really cheap ones --- but it used to be that
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they were often junk and sometimes could not be disabled
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--- even if they had jumpers that purported to do so).
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<br><br>
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Anyway, good luck.
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<br><br>
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Personally I usually configure a "dumb terminal" port
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for all of my Linux boxes (eventually). This serves two
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important purposes: It is the most convenient way for me
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to get files to and from my laptop (for which I don't have
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a supported ethernet card). More importantly it gives me
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an extra troubleshooting option if my system "seems" hung.
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I can just plug in the old null modem and give it a go.
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<br><br>
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It can mean the difference between a clean shutdown and a
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game of "red-switch" roulette.
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<br><br>
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(Although it hasn't happened for any of my systems in so
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long I've almost given up on seeing it at all
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<img src="../gx/dennis/smily.gif" alt=";)"
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width="20" height="24" align="absmiddle"> --- but it
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used to be possible for the Linux console driver be completely
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unresponsive, and even for the network subsystem to be dead
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while the serial lines were still accessible. However, if
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you don't configure the terminal line in advance you don't have
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the option when you want it).
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</blockquote>
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<P> <hr> <P>
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<H5 align="center"><a href="http://www.linuxgazette.com/copying.html"
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>Copyright ©</a> 1998, James T. Dennis <BR>
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Published in <I>Linux Gazette</I> Issue 29 June 1998</H5>
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<P> <hr>
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<td><A HREF="tag_versions.html">versions</A></td>
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<td><A HREF="tag_winmodem.html">winmodem</a></td>
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<td><A HREF="tag_dell.html">dell</a></td>
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<td><A HREF="tag_dumbterm.html">dumbterm</a></td>
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<td><A HREF="tag_ppp233.html">ppp233</a></td>
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