Developers use serial connections to capture boot logs and debug operating system kernels (e.g., Windows debugging via WinDbg over COM).
While it rarely prevents the guest operating system from loading, it creates a persistent, annoying popup at every single launch. Understanding why this happens and applying targeted fixes will help clear your hypervisor logs and ensure a seamless boot sequence. Root Causes of the Serial0 Disconnection Error
While it rarely prevents the guest operating system from loading entirely, it creates an disruptive startup pop-up and breaks features tied to serial connectivity—such as legacy printing subsystems or hardware debuggers. Root Causes of the Error virtual device serial0 will start disconnected
The virtual port is mapped to a physical COM port on your host computer (e.g., COM1cap C cap O cap M 1
Once the most likely cause has been identified, you can follow these targeted solutions. Developers use serial connections to capture boot logs
It typically appears as a pop-up window immediately after you power on a virtual machine (VM). While it often looks like a critical error, it is usually just a configuration notification.
Navigate to the VM folder and open the .vmx file with a text editor (e.g., Notepad). Look for lines starting with serial0 . Ensure they look similar to this for a pipe connection: serial0.present = "TRUE" serial0.fileType = "pipe" serial0.fileName = "\\.\pipe\yourpipename" serial0.startConnected = "TRUE" Save and close the file, then restart the VM. 4. Troubleshooting: When the Serial Port is Needed Root Causes of the Serial0 Disconnection Error While
The error message "Virtual device serial0 will start disconnected"
The virtual machine flickered to life. Lines of code scrolled upward—white on black, a waterfall of data—but as the OS reached its final handshake, the screen went dark. No login prompt. No desktop. Just a blinking underscore in the top-left corner, pulsing like a failing heart.
This message typically appears in or VMware Fusion when a virtual machine (VM) is configured to look for a serial port that is unavailable, invalid, or belongs to a legacy feature no longer supported. Why it Happens
Starting with VMware Fusion 13.5 and Workstation 17.5 , VMware officially retired , a legacy technology that mapped printers via a virtual serial port (serial0). Because the software no longer supports the "thinprint" file type, it flags it as an invalid value and tells you the device will start disconnected.