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Wondering if anyone knows of a solution to connect with telnet/ssh through a rs232 serial port

Edit:

I am looking for a way to connect to computers together via a serial port. I want to be able to view the file system of a computer through a serial port.. Is this possible?

Edit:

So I have successfully connected two computers together using r232 serial ports with a null modem. The instructions I have used are located here

Now how do I get to the file system of the host computer??

Any ideas?

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I put an answer for a solution to connect to a device via Serial port. If that's not what you were looking for, then please expand upon your question--it was a little confusing. –  Theo Apr 14 '11 at 12:49
    
Keep in mind that, once you get this lashup working, the data rate will be only slightly better than smoke signals. You'll transfer data far faster with a USB stick or such (and do much better with USB-to-USB "null modem" connection). –  Daniel R Hicks Jul 1 '12 at 12:07
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8 Answers 8

up vote 3 down vote accepted

It is completely feasible and is in fact the essence of pre-GUI Unix'es, circa 1970, that this was the only modus operandi available to connect a console terminal to a Unix computer. The legacy of this convention is still with us (and it is not anachronistic though perhaps obscure and subliminal in today's micro-computer systems) and available, especially with embedded systems that lack consoles with builtin keyboards and monitors like the actual devices at plugcomputer dot org as described in the article

slash plugwiki slash index dot php slash Setting_up_Serial_Console_Under_Linux
(Sorry, new users can only post a maximum of two hyperlinks)

(Marvel's U-Boot is the host computer's Linux OS derivative).

There are two issues that need to be addressed.

  1. The physical connection is only part of the answer as already discussed.

  2. A CLI (command line interpreter) or other console terminal interface running on the host is also required.

Details:

step 1. The physical connection can be tested (and hardware settings controlled such as port selected, baud rate, parity, etc.) with utilities like: moserial, gtkterm, minicom, putty, ... with elementary data and file transfer capabilities.

(Somewhat obtusely, the next step, 2, is not needed if ls >dir-list.txt is done on one machine and then a utility (like moserial) is used to send the directory listing file to the other.)

step 2. To actually use the connection to control the host from the client requires a command interface on the host using utilities like: getty, screen, ... . Here are basic descriptions of using getty or the screen Ubuntu lucid manpages to do it. The client can often use just a "simple" serial port communication utility as in step 1. Programs such as screen or kermit are usually run on both host and client machines. If using gkermit on the host though, a console communication session must already be established, such as with getty.

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PuTTY can do all of the above, if you are talking about a direct serial connection (plug in cable, etc.)

Install, then open putty and select "Serial". Check the port settings, then Open.

Then, plug in cable and boot up device.

EDIT: To connect two computers together via serial port requires a null modem cable. It's a serial cable that has the inputs and outputs crossed (similar to a Ethernet Crossover Cable). This enables the two computers to talk to each other.

You will also need PuTTY (or a terminal emulator) on both computers, and use the correct COM ports for both computers. Also ensure the other settings are the same (baud rate, etc.)

Once you open them, they should connect. However, no program will be running, because it's just a direct connection. But it's a start.

A little more detailed explanation can be found at this question: Serial connection between 2 computers

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@Theo cool, what would I have to do on the host side? –  Richard Apr 14 '11 at 12:49
    
What are you connecting together? The computer you install PuTTY on is the host, unless you're talking about connecting two computer together--that is a completely different question. –  Theo Apr 14 '11 at 12:53
    
@Theo: My question was not clear. I am trying to connect two computers together via a com port. –  Richard Apr 14 '11 at 12:54
    
@Theo: Did you know that you can just download putty.exe and not go through any install process? –  Kevin M Apr 14 '11 at 12:56
    
@Kevin: Yes, but the other programs are useful too! Also, the file system becomes more difficult to do, as with the serial connection you'll pretty much see nothing. Does this have to be serial? –  Theo Apr 14 '11 at 13:02
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What you're attempting to do is known as "SLIP". http://en.wikipedia.org/wiki/SLIP

Natively supported in *nix. What platforms are you using?

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Windows XP Pro –  Richard Apr 14 '11 at 12:58
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wrinkles:

case 3. Network file sharing connectivity only, has limitations.

While it is also possible to establish a file sharing network connection, this does not allow arbitrary processes to be started on the host from the client. It does allow clients to surf host folders and "view" their contents but this does not provide for the capabilities that telnet does as quoted in the original post.

case 4. However activating a full fledged network layer suite of software (TCP/IP) on a serial port (SLiP) can again provide client services such as telnet.

Abstractly, once a physical connection is made, installation of networking support is optional which dictates the final suite of compatible software the host and client run.

The suite of software that the host and client can use depends on the networking software needed. Programs like many kermit versions are oblivious to the manner in which machines connect as long as a physical connection exists, arbitrarily able to navigate most network layers,. This is not the case with gkermit which does require getty support though TCP/IP networking is not needed. And some programs like a legacy Atari kermit can only use a raw physical connection devoid of any networking software.

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I believe standard file sharing should work at that point - tried sharing a folder the usual way, using windows file sharing?

Though.. serial ports at this point are rather obscure so.. not entirely sure if they work like a normal networking link

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Today's microcomputers often lack RS232 9 pin (let alone 25 pin) interfaces but Ubuntu seamlessly supports common USB to 9 pin serial adapters. Currently, a circa 1980 Atari ST with a 25 pin serial port is connected to a 2011 model netbook with only USB serial ports using such an adapter with a 25 to 9 pin adapter and a null modem adapter. The Atari came with a VT52 terminal emulator accessory to control a Lucid getty to start gkermit. The VT52 emulator is then stopped and the Atari version of kermit is then run to complete file transfers.

Check out

http://www.plugcomputer.org/plugwiki/index.php/Setting_up_Serial_Console_Under_Linux

using the headless (no console display or keyboard) devices at http://www.plugcomputer.org.

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In the '80's I used to use a program called FastLynx.

It showed a two paned window with the local file system on one side and the other system on the other.

You could cut paste transfer and view files on both panes.

Works with DOS, Windows and Linux.

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To connect via telnet/ssh over an RS-232 port, the following is needed:

  • Computers must be connected via a null-modem cable

  • Computers must be running a PPP daemon, service, or software that is bound to the serial port. PPP is what lets you do IP over the serial port. It's needed if you want to do standard TCP/IP telnet, ssh, or anything else TCP/UDP/IP over a serial port. Windows supports this, but read on.

  • In the case of Windows, you have additional work to do since Windows does not support PPP unless you have a modem connected to that serial port. Windows sends out AT commands trying to talk to a modem before it starts PPP. So you need something on the other end that can respond as if it were a 56k modem and emit the expected chat text to the Windows system. On Linux, it's easy to tell pppd to do that. Don't know how to do that if the "remote" system is also a Windows system.

Basically, the third point is the problematic issue with getting Windows file sharing working over a serial connection.

If you have an old computer with 2 serial ports, you could slap Linux on that, connect each system to the intermediary computer, start up ppp (with the Windows chat text support) on each serial port, make sure ipv4 forwarding is enabled, and it would work well.

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