Virtual Device Serial0 Will Start Disconnected !!link!! -

A virtual machine uses a configuration file (often a .vmx file) to define its hardware, such as hard drives, network adapters, and serial ports. "Serial0" refers to the first serial port ( COM1 ) assigned to the virtual machine.

(Advanced)

Remove vestigial hardware like serial ports, parallel ports, and floppy drives from golden master images and VM templates before deploying them at scale.

: Ensure the correct serial WIC (like a WIC-2T) is installed in the appropriate slot on the router before you power it on and attempt to create links.

A: No. Snapshots and clones remain unaffected. The disconnected serial port does not hold any state. virtual device serial0 will start disconnected

: Another application or virtualization service on the host may be using the COM port that the VM is trying to occupy.

The easiest way to resolve this is to remove the legacy printer device that is causing the conflict. your virtual machine completely. Open the Virtual Machine Settings . Find Printer in the list of hardware devices. Select it and click Remove . Click OK and restart the VM. Option 2: For VMware Workstation Users

For a serial link to function, one side must be a DCE (Data Circuit-terminating Equipment) and the other a DTE (Data Terminal Equipment). The DCE side is responsible for providing the clocking signal to the DTE side. In a lab environment, when two routers are connected back-to-back with a serial cable, one router must act as the DCE. If the DCE side is not configured with a clock rate , the line protocol will remain down. You can determine which role an interface is playing using the show controllers serial0 command.

| 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 ). | A virtual machine uses a configuration file (often a

Which and version are you using (VMware Workstation, ESXi, Fusion)?

: The message may appear if you have not properly installed the correct WIC (e.g., a WIC-2T for serial ports) into the router's slot before linking devices. GNS3 will not recognize a serial interface if the underlying hardware module is not present in the router's configuration.

The VM configuration is looking for a physical serial port ( COM1 , COM2 , etc.) on your modern host computer, but modern motherboards rarely feature these legacy ports.

To improve boot performance and prevent unnecessary I/O delays, serial0 (the primary virtual serial device) now starts in a by default. The serial interface will only become active after an explicit connection is established by the user or guest OS. : Ensure the correct serial WIC (like a

This dual usage of the message highlights that the underlying concept—a virtual device that is not yet active—is consistent across different virtualization platforms.

Look for lines like:

Another application or VM is already using the host's COM port.

If you tell the VM to connect to COM1 on the host, but that port is already in use by another host application (e.g., a real terminal program, a PLC programming tool, or another VM), VMware will not forcibly steal the port. Instead, it starts the VM with that device disconnected and logs this warning.

Make sure: