Writing Data to Virtual Serial Port: Host-Guest Issue in MacOS-Ubuntu Setup

Introduction

This article outlines the process of setting up a serial connection between a MacOS host and a Ubuntu Server 20.04 guest virtual machine (VM) using VirtualBox and the socat command. This connection is essential for data transfer between the two systems.

Prerequisites

Before proceeding, ensure the following:

• Both the host and guest systems have a stable internet connection.
• VirtualBox is installed on the host system.
• Ubuntu Server 20.04 is installed as a guest VM using VirtualBox.

Setting up Serial Ports with socat

To create two virtual serial ports, use the following socat command:

 socat -d -d -T 10 - < /dev/tty.usbmodem0 38400 & socat -d -d -T 11 < /dev/tty.usbmodem1 38400
 

This command creates two serial ports, numbered 10 and 11, and assigns them to the first available USB serial port (/dev/tty.usbmodem0) and the second available USB serial port (/dev/tty.usbmodem1), respectively. Both ports are set to a baud rate of 38400.

Configuring VirtualBox

Next, configure the guest VM to use the serial ports:

1. Start the Ubuntu Server 20.04 VM in VirtualBox.
2. Open the settings for the VM.
3. Navigate to the "Serial Ports" tab.
4. Add two new serial ports, assigning them the numbers 1 and 2.
5. Set the input and output settings for each serial port as follows:

 Port number: 1
 Device: /dev/ttyS0
 Host port: /dev/ttyUSB0
 Input settings: None
 Output settings: None
Port number: 2
Device: /dev/ttyS1
Host port: /dev/ttyUSB1
Input settings: None
Output settings: None

Configuring Ubuntu Server 20.04

Finally, configure the Ubuntu Server 20.04 guest system to use the serial ports:

1. Log in to the Ubuntu Server 20.04 VM via SSH or the console.
2. Install the necessary packages:

 sudo apt update
 sudo apt install socat
 

Now, create a systemd service file to start socat at boot:

 sudo nano /etc/systemd/system/socat.service
 

Add the following content to the file:

 [Unit]
 Description=Serial communication with socat
 After=network-online.target
[Service]
User=root
WorkingDirectory=/
ExecStart=/usr/bin/socat - UNIX-CONNECT:/dev/ttyS0:38400,raw,echo=0 STDIN,raw,echo=0:11:38400,raw,echo=0
Restart=on-failure
[Install]
WantedBy=multi-user.target

Save and close the file.

Reload the systemd daemon:

 sudo systemctl daemon-reload
 

Start the socat service:

 sudo systemctl start socat
 

Check the status of the socat service:

 sudo systemctl status socat
 

This article outlined the process of setting up a serial connection between a MacOS host and a Ubuntu Server 20.04 guest VM using VirtualBox and the socat command. By following the steps outlined in this article, you can create two virtual serial ports, configure VirtualBox and Ubuntu Server 20.04 to use these ports, and establish a reliable serial connection between the two systems.