How can I set up virtual serial ports (Linux null modem emulator) using tty0tty

Question

I want to set up a virtual serial port emulator in Linux. I want the ports to be permanent, so that I can use them every time I restart. I tried using socat for that purpose in this way,

socat -d -d pty,raw,echo=0 pty,raw,echo=0

But I often get "port busy" issues during the usage of these VSPs (Virtual Serial Ports) in my test programs. Also, I find it hard to create permanent/persistent VSPs.

I now want to try out tty0tty for my purposes. But I have found little documentation on how to use it. Can anyone enlighten me on this? Please do comment if there are any solutions for socat as well.

Answer 1

Installation

1. Download the tty0tty package from one of these sources:

   • http://sourceforge.net/projects/tty0tty/files/

   • clone the repo https://github.com/freemed/tty0tty:

     git clone https://github.com/freemed/tty0tty
     

2. Extract it:

   tar xf tty0tty-1.2.tgz
   

3. Build the kernel module from provided source:

    cd tty0tty-1.2/module
    make
   

4. Copy the new kernel module into the kernel modules directory:

    sudo cp tty0tty.ko /lib/modules/$(uname -r)/kernel/drivers/misc/
   

5. Load the module:

    sudo depmod
    sudo modprobe tty0tty
   

   You should see new serial ports in /dev/ (ls /dev/tnt*)

6. Give appropriate permissions to the new serial ports:

    sudo chmod 666 /dev/tnt*
   

You can now access the serial ports as /dev/tnt0 (1,2,3,4 etc) Note that the consecutive ports are interconnected. For example, /dev/tnt0 and /dev/tnt1 are connected as if using a direct cable.

Persisting across boots

Edit the file /etc/modules (Debian) or /etc/modules.conf

sudo nano /etc/modules.conf

and add the following line:

tty0tty

Warning

Note that this method will not make the module persist over kernel updates so if you ever update your kernel, make sure you build tty0tty again repeat the process.

If you don't move the module on every kernel update systemctl --failed will return that service systemd-modules-load.service ended "failed". Also on journalctl -xe | grep "Failed to find".