Is there a way to connect to a serial terminal just as you would do with SSH? There must be a simpler way than tools such as Minicom, like this

I know I can cat the output from /dev/ttyS0 but only one way communication is possible that way, from the port to the console. And echo out to the port is just the same but the other way around, to the port.

How can I realize two way communication with a serial port the simplest possible way on Unix/Linux?

14 Answers

I find screen the most useful program for serial communication since I use it for other things anyway. It's usually just screen /dev/ttyS0 <speed>, although the default settings may be different for your device. It also allows you to pipe anything into the session by entering command mode and doing exec !! <run some program that generates output>.

Background

The main reason why you need any program like minicom to communicate over a serial port is that the port needs to be set up prior to initiating a connection. If it weren't set up appropriately, the cat and echo commands would not do for you what you might have expected. Notice that once you run a program like minicom, the port is left with the settings that minicom used. You can query the communication settings using the stty program like this:

If you have done it right; after booting the computer and before running any other program like minicom, the communication settings will be at their default settings. These are probably different than what you will need to make your connection. In this situation, sending the commands cat or echo to the port will either produce garbage or not work at all.

Run stty again after using minicom, and you'll notice the settings are set to what the program was using.

Minimal serial communication

Basically, two things are needed to have two-way communication through a serial port: 1) configuring the serial port, and 2) opening the pseudo-tty read-write.

The most basic program that I know that does this is picocom. You can also use a tool like setserial to set up the port and then interact with it directly from the shell.

I found a way using a shell script here that put cat as a background process and a while loop that read the user input and echo it out to the port. I modified it to be more general and it fitted my purpose perfectly.

If UUCP is installed on the system, you may use the command cu, e.g.

Try http://tio.github.io

'tio' is a simple TTY terminal application which features a straightforward commandline interface to easily connect to TTY devices for basic input/output.

Typical use is without options. For example:

Which corresponds to the commonly used options:

It comes with full shell auto completion support for all options.

This script is based on another answer, but sends everything over the serial port (except Ctrl+Q), not just single commands followed by Enter. This enables you to use Ctrl+C or Ctrl+Z on the remote host, and to use interactive 'GUI' programs like aptitude or alsamixer. It can be quit by pressing Ctrl+Q.

BTW, the putty package (which does run on Linux) does include serial support.

It depends on what you want to do. Do you want to run a shell or applicaiton interactively from the terminal, connect out to another computer over the serial line, automate communication with a device over a serial port?

If you want bidirectional communication then I presume you want something interactive with a human on the terminal. You can configure the system to allow logins from a terminal over a serial port by seting up a getty(1) session on the serial port - getty is the tool for setting up a terminal and allowing logins onto it. Put an entry in your inittab(5) file to run it on the appropriate serial port on a respawn basis.

If you want to connect to a device and initiate automated two way conversations then you could see if expect will get you what you want. Use stty(1) to configure the port to the right parity, baud rate and other relevant settings.

If you want to communicate interactively with another computer over the serial port then you will need terminal emulation software. This does quite a lot - it sets up the port, interprets ANSI or other terminal command sequences (ANSI was far from being the only standard supported by serial terminals). Many terminal emulators also support file transfer protocols such as kermit or zmodem.

The ins and outs of serial communications and terminal I/O are fairly complex; you can read more than you ever wanted to know on the subject in the serial howto.

Putty works well on Linux and offers some convenience, especially for serial communications. It has one drawback I haven't been able to directly solve: no copy-paste from the Putty window itself. The windows version has a lovely auto-copy to clipboard on highlight, right-click to paste behaviour (and there are excellent plugins for both chrome and firefox to enable the same behavior), but on Linux, no copy love AFAIK.

If the lack of copy is a problem (it is for me) then turn on logging in putty and open a standard terminal window and # tail -f putty.log and bidirectional text is available for standard copypasta action.

As mentioned before you can try picocom. The latest release (2.0) can also be used (safely) to set-up a 'terminal server' since it no longer permits shell command injection. See:

Another issue that can occur is that your user account may need to set to the 'dialout' group to access the serial port.

You might want to take a look at

Pro: doesn't have obvious security problems like minicom or picocom (if you don't have a problem giving the users shell access, no problem, but you most likely do have one if you want to set up a terminal server...)

You need to be sure to have the correct read write permits on the device, you could see it with:

I rely on the script you found and made some modifications.

For the development systems I've used by now, they used to need:

• None parity and
• One stop bit

Those values are the default ones in the script.

So in order to connect, you can use it as simple as follows:

Example:

Script:

P.S.: You need to know which kind of line feed is using your receiver system since this will determine how you'll need to send the commands in my case I needed a Windows like LF, means that I need to send

ASCII values for:

• LF : 0Ah, line feed 'n'
• CR : 0Dh, carrige return 'r'
• BS : 08h, back space '<-'

As it is not mentioned here already, I'd also mention socat - more info in https://stackoverflow.com/questions/2899180/how-can-i-use-com-and-usb-ports-within-cygwin :

or

(though, I've had the problem of stopping it once it starts running, under MSYS2 on Windows)

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