Virtual Device Serial0 Will Start Disconnected -

The message is a configuration notification rather than a critical error. It implies the VM cannot find the backend resource for the serial port. Most users can ignore it or disable the port in settings. If you require the port, reconfiguring the mapping to a valid file, pipe, or physical port will eliminate the warning. For more in-depth troubleshooting, I can:

If you select "Physical serial port" but leave the "Connect at power on" box , you will see this message.

If you want to keep the device for occasional use but stop the error message at startup: Go to . Select the Serial Port hardware. Uncheck the box for "Connect at power on" .

"virtual device serial0 will start disconnected" is when you've enabled a serial port but not defined a live connection. It does not indicate a problem with your virtual machine or device.

If you need the serial port to exist for software configuration purposes, but you don't need it connected to anything immediately, you can simply stop it from trying to connect at boot. the virtual machine. Open the VM settings. Select Serial Port 1 . Uncheck the option Connect at power on . Click OK . Solution 3: Reconfigure the Serial Port virtual device serial0 will start disconnected

Method 1: Remove the Serial Port (Recommended for Most Users)

Interestingly, a very similar message appears in other technology contexts, most notably when running virtual machines (VMs). In Proxmox VE, when you configure a VM with an emulated serial port and instruct the OS to use it as a console, the hypervisor may display that serial0 will start disconnected. This is typically not an error in Proxmox but a normal part of the VM configuration, as the virtual serial port is only connected when a terminal program (like Minicom or Putty) attaches to it.

Scroll down the virtual hardware list until you locate .

Most modern virtual machines (Windows 10/11, Linux servers, Ubuntu) do not require a physical serial port. Removing it is the best way to get rid of the warning. your virtual machine. Open the VM settings in VMware Workstation/Player. Select Serial Port 1 (or Serial0 ). Click Remove . Click OK and start the virtual machine. Solution 2: Disable "Connect at Power On" The message is a configuration notification rather than

Depending on whether you actually need the serial port, use one of the following methods to resolve the message.

| Interface Status | Line Protocol Status | Typical Cause | Recommended Action | | :--- | :--- | :--- | :--- | | Administratively down | down | Interface has been manually shut down. | Enter interface config mode and use the no shutdown command. | | down | down | Physical layer problem, e.g., no cable, faulty hardware, or no power from remote device. | Check physical connections, try swapping cables, and verify the remote device is powered on. | | up | down | Data link layer problem, common causes include a missing clock rate on the DCE side or mismatched encapsulation protocols. | Verify which side is DTE/DCE and set the clock rate if necessary. Check the encapsulation (e.g., HDLC or PPP). | | up | up | Interface is operational. | - |

If you configure the serial port to connect to a named pipe (used for debugging kernel-mode code or connecting two VMs) but the pipe name is wrong or the target application isn't listening, VMware will disconnect it at startup.

The VM is configured to map serial0 to a physical COM port on the host machine, but the host lacks a physical serial port or the port is disabled in the host BIOS. If you require the port, reconfiguring the mapping

Modern operating systems and software rarely rely on serial communication. If you do not explicitly use legacy hardware debugging, specialized console connections, or ancient peripherals, the cleanest fix is to delete the virtual device entirely.

The method for resolving the warning depends on whether your VM is running on a Windows/Linux host or a macOS environment.

The VM configuration file ( .vmx ) may be instructed to map serial0 automatically to a physical COM port on the host machine. If the physical host laptop or desktop lacks a physical DB9 serial port, or if the port is disabled within the host machine’s BIOS/UEFI, initialization fails.

Virtual serial ports serve as the communication channel between a debugee VM (the one being debugged) and a debugger VM running WinDbg or GDB. For kernel debugging, the debugee VM's serial port must be connected to a named pipe with the appropriate server/client roles. The error "Virtual device serial0 will start disconnected" in this scenario often means the named pipe could not be created or the remote debugger is not yet listening. Ensuring the debugger process is active before powering on the debugee VM resolves the issue in most cases.

For the vast majority of virtualized workloads, it is harmless informational output. But if serial communication is critical to your guest OS or application, the warning serves as a useful reminder to attach your virtual cable before booting.

For more detailed guides, you can visit the Broadcom/VMware Knowledge Base or the VMware Fusion community discussions . If you’d like, let me know: