In Need of Advice

Tim Chase blinux.list at
Mon Sep 5 17:35:04 UTC 2011

On 09/05/11 11:54, RiverWind wrote:
> I do not believe that using my modem in order to dial up my
> Linux machine would work, but I also know that there is such a
> thing as a "NUL" modem cable???

It depends on what you want to do.  If you want your DOS machine 
to simply be a dumb terminal (using your "Commo" program), and 
not running any real/internet applications on your DOS machine, 
then you can set it up pretty easily.  If you want to run 
internet-aware programs on your DOS box it depends on how you 
connect to the internet:  if you have dial-up, then you can have 
either machine do the dialing and just refrain from using them at 
the same time; whereas if you have an always-on connection (DSL, 
cable, FIOS, etc), you can either share that connection with a 
dedicated router (and have both your Linux box and your DOS box 
plugged into that router) or have your Linux box act as a router 
to share your connection with your DOS box (though this would 
either require a second network-card in your Linux box, or some 
chicanery to share the internet connection over a serial line 
(i.e. a null-modem serial cable).

If you're just using your DOS machine as a terminal with "Commo", 
you can edit your /etc/inittab to uncomment a line with "getty" 
to listen on a corresponding port.  If your Linux box has a real 
serial port, it would be a line something like

   /sbin/getty -L ttyS0 9600 vt100

which roughly means "spawn a virtual terminal, listening on 
/dev/ttyS0 (COM1 if you booted the machine in DOS) at 9600 baud, 
and act like a standard VT-100 terminal"  I believe that it 
defaults to the comm settings of "N81".  You would then just 
connect a null-modem cable between the machines' serial ports and 
point your DOS machine's terminal software at its comm port at 
9600,n,8,1 and you should find your login prompt ready to go.

If your Linux box doesn't have a real serial port, you can get a 
USB-to-Serial dongle that gives you a serial port...usually at 
/dev/ttyUSB0 or something of the sort.  You'd just tweak the 
above inittab line to have that terminal ("ttyUSB0") instead of 

Because the /etc/inittab file is a protected file, you'd have to 
edit as root either with

   bash$ sudo $EDITOR /etc/inittab


   bash$ su
   (type in the admin/root password)
   bash# $EDITOR /etc/inittab

where "$EDITOR" is your editor of choice (vi, ed, vim, pico, 
nano, emacs, joe, etc).

Once you've uncommented/edited the line to have the settings you 
want, you can issue (again, as root either via "su" or "sudo")

   telinit Q

to tell the main process to re-read the /etc/inittab

You can read up on that at "man telinit".

> I would appreciate any and all advice I can get regarding
> this matter, so that I won't need to pay for an ISP when I
> already have one.

Unless you're using some proprietary ISP that doesn't play well 
with Linux (AOL used to be bad about this), you shouldn't have to 
pay twice for a connection.  Either it's dial-up and you just let 
one computer use it at a time or you use one machine to connect 
and share the connection with the other; or you have a dedicated 
DSL/cable/FIOS line and you have a router sharing the connection 
(whether that router is a dedicated box like a Linksys/DLink, or 
your Linux box acting as a router).

I hope this gives you some decent info to get you pointed in the 
right direction.


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