Can docker virtual serial port?

Docker is a common virtualization tool for many developers and system administrators. It can package many applications into a container that can execute on all platforms without modification. However, in some application scenarios, users need to use a serial port or serial device. So can Docker virtual serial ports?

In the Linux operating system, serial port devices are represented by /dev/ttyS0 to /dev/ttyS3 device files. They can be used to connect devices such as printers, modems, digital meters, and more. Serial port is a simple and reliable communication method. However, within Docker, the Docker container does not have its own physical hardware device, so the physical serial port device cannot be used by default.

However, Docker provides a mechanism called "device mapping" that can map virtual or physical devices on the host to inside the Docker container. In this case, you can simulate serial communication by mapping the serial device on the host machine into the Docker container.

When starting a Docker container, device mapping can be achieved by adding the "--device" option. For example, the following command maps the /dev/ttyUSB0 device into the Docker container's /dev/ttyUSB0 device file:

$ sudo docker run -it --name mycontainer --device=/dev/ttyUSB0 ubuntu:latest

After starting the container, run the following command inside the container to verify that the serial port is available inside the container:

$ ls -l /dev/ttyUSB0

Running the following command inside a Docker container will attempt to open the serial device:

$ minicom -D /dev/ttyUSB0

If you do not install the serial port driver on the host, the container will not have access to the device. Therefore, before starting the container, install the necessary drivers.

Also, although it is possible to use serial ports in Docker containers using device mapping, it is not an ideal solution because device mapping will be very tricky if you need to connect multiple serial devices at the same time. In this case, a better solution is to use a virtual serial port.

Virtual serial port is a method of simulating serial port communication by mapping the host serial port device to a virtual serial port device. This virtual serial device looks like a real serial device, but it is actually just a real serial device that transmits data to the host. In a Docker container, you can use tools such as socat or ttyd to create virtual serial devices.

The following is the command to use socat to create a virtual serial port device:

$ sudo socat pty,link=/dev/ttyS0,raw,echo=0 pty,link=/dev/ttyS1,raw,echo=0

After running this command, socat will create two virtual serial port devices /dev/ttyS0 and /dev/ttyS1, which can be used to simulate serial communication.

Then, use the following command to map the virtual serial port into the container when starting the Docker container:

$ sudo docker run -it --name mycontainer -v /dev/ttyS0:/dev/ttyS0 ubuntu:latest

Inside the container, you can try to open the /dev/ttyS0 device for serial communication.

Summary

Although Docker does not support serial devices by default, you can use device mapping or virtual serial devices to simulate serial communication. When choosing a solution, please note that device mapping can become very troublesome when connecting multiple serial devices, while using virtual serial ports can easily achieve multiple serial port connections.

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