How to Use a Serial Port in VMware Virtual Machines

Configuring Serial Ports in a VMware Workstation

Adding a serial port (or COM port) to a virtual machine (VM) allows you to interact with serial devices like routers or development boards within the VM environment. There are many ways you can connect a virtual serial port, including connecting to a physical port, file, named pipe, and network.

Virtual machines can have a maximum of 32 COM ports. However, when creating a VM, you can actually choose not to include any at all. If you choose that approach, the guest operating system (the OS running inside the VM) simply won't see any available serial ports.

Requirements

Before adding a virtual serial port, ensure that your virtual machine is turned off already.

Make sure that you’re aware of the right media types and vSPC connection details relevant to your port configuration. You also need to grant a “Virtual Machine .Configuration.Add or Remove Device” privilege to continue.

Specific connection types have unique prerequisites, too. For example, the following firewall rule sets are needed if you want to use your serial port over a network:

1. VM serial port connected to vSPC. Enable the “Use virtual serial port concentrator” option to facilitate only outbound signals from the host computer.
2. VM serial port connected over network. This is basically the same as the first rule set, except that it doesn’t use the virtual serial port concentrator (vSPC).

With that established, here’s how you configure a VMware virtual serial port.

Adding a VMware Virtual Serial Port

1. In the inventory, right-click your chosen virtual machine and select “Edit Settings”. Switch to the “Hardware” tab and click “Add”.
2. Expand the drop-down menu and choose “Serial Port”. A new serial port will appear on your list of devices.
3. Open the “New Serial port” drop-down menu and choose your preferred connection type (physical port, file, named pipe, or network). Then, click “OK” to finish.

Serial Port Connection Types

Depending on what kind of data processing you want to achieve, you need to select a particular connection type for your virtual serial port. Here’s a quick breakdown of the four different connection methods you can use:

1. Physical serial port: This is the most common setup, allowing the VM to interact with physical devices like modems.
2. File on the host computer: Data sent through the virtual port is written to a file on the host computer. This allows you to record information about certain processes running in your VM, which is useful for logging communication.
3. Host-side named pipe: This creates a direct connection for data exchange between the VM and an application or another VM on the host machine. Think of it as connecting two separate machines with a serial cable, except that they’re on a single computer. It’s a common method used for remote debugging.
4. Network port or vSPC URI: This uses the virtual serial port concentrator (vSPC) to establish the connection over the network. In other words, you use this mode to communicate between the virtual serial port and a remote device.

Outputting to a Named Pipe

If you selected a named pipe connection in the “New Serial port” drop-down menu, click the “Pipe Name” field and type your preferred name (e.g., “\\.\pipe\namedpipe”).

You can simply use the default name provided if you’re using a Windows host computer. Just make sure that you use the same name on both the server and the client.

Then, from the drop-downs available, choose “Near end” and “Far end” of the pipe.

Server vs Client Mode for Network Connections

If you choose a network connection type, you can also select whether to set up your serial port for a client or server connection.

If you opt for a server connection, you gain control over the virtual machine connected to your serial port. It makes your VM act like a server, waiting for an incoming connection from your host. This is ideal for scenarios where you want occasional control over the VM, like during debugging or configuration.

Meanwhile, choose a client connection if you want to use your virtual machine as the client. In other words, the VM actively initiates the connection to a designated program upon startup. It’s common for logging applications where you automatically send data to another system.

Creating Serial Port Network Connections Without Authentication Parameters

To configure your VM with a serial port server connection with a telnet://:11111 URI (Uniform Resource Identifier), run the following command.

Meanwhile, you can also set up your serial port using a client connection by running the Telnet Server on Linux on port 11 (telnet://yourLinuxBox:11). Use the following command.