For advanced users needing the port to start connected (e.g., for debugging or specific hardware mapping), ensure these lines exist in your .vmx file: serial0.present = "TRUE" serial0.startConnected = "TRUE"
| Platform | Typical Reason | | :--- | :--- | | | The serial port is set to "Use named pipe" or "Use output file", but the other end (e.g., a debugger like WinDbg) hasn't connected yet. | | VirtualBox | Serial port is enabled with "Port Mode" set to "Disconnected". | | GNS3 / EVE-NG | The virtual router or switch has a serial interface (e.g., serial0/0 ), but it's not linked to another device's serial interface via a cable. | | QEMU | The -serial option is used without a backend (e.g., -serial null or -serial unix:/path,server=off ). | virtual device serial0 will start disconnected
Another application or VM is already using the host's COM port. For advanced users needing the port to start connected (e