This warning message, , is one of the most common errors seen by users of VMware Workstation, VMware Player, and VMware Fusion.
: The VM is set to connect to a physical COM port on your host machine that does not exist or is currently being used by another application.
What Does "Virtual Device Serial0 Will Start Disconnected" Mean?
If your workflow requires an active virtual serial port (e.g., for kernel debugging, firmware development, or connecting legacy Cisco equipment), you must route the connection to a valid resource instead of a missing physical port. Open the virtual machine and select Serial Port . virtual device serial0 will start disconnected
The statement “virtual device serial0 will start disconnected” typically appears in virtualization, emulation, or hardware abstraction contexts (e.g., QEMU/KVM, VirtualBox, containerized device passthrough, or network/device simulators). It means the emulated or virtual serial interface named serial0 is configured so that, at VM or system boot, it has no active connection endpoint—no host pipe, socket, file, console, or physical device attached. The device exists in the guest’s device tree but is not linked to any I/O endpoint until explicitly connected.
Right-click the virtual machine in your library and select .
: The .vmx file contains legacy settings or invalid values for the serial0 parameter. How to Fix the Error This warning message, , is one of the
the virtual machine completely (do not just suspend it).
Completely the virtual machine (do not just suspend it).
Locate and open the .vmx file using a text editor like vi or Notepad++. Search for lines beginning with serial0 . If your workflow requires an active virtual serial port (e
The VM configuration is actively looking for a physical serial port (like a 9-pin D-sub connector) on your host computer, but your modern desktop or laptop does not have one.
If you actually need a serial port (e.g., for debugging), ensure it is mapped to a valid resource. Go to > Serial Port .
The resolution depends on your specific needs and configuration:
Virtual serial ports require a valid backing mechanism to function. The error triggers when VMware cannot initialize the connection type specified in the VM configuration.
In the tab, look through the device list for Serial Port (often labeled Serial Port 1 or serial0 ). Click on the Serial Port to highlight it. Click the Remove button at the bottom of the window. Click OK to save the changes and start your VM. For VMware vSphere / ESXi Web Client: Log into your vSphere or ESXi client dashboard. Turn off the target virtual machine. Right-click the VM and choose Edit Settings .