Virtual Device Serial0 Will Start Disconnected May 2026
The message "Virtual device serial0 will start disconnected" is the emulator's honest way of telling you, "I have no information about what this port should connect to, so I am leaving it in a safe, disconnected state."
Do not fear it. Understand it.
By internalizing this behavior, you stop fighting the emulator and start learning the networking. And after all, the goal of a virtual lab is to emulate the real world—where unplugged cables mean disconnected circuits.
Now go build your topology, connect those serial cables, and watch show interface serial0 finally display the glorious words: "Serial0 is up, line protocol is up."
Troubleshooting VMware: "Virtual device serial0 will start disconnected"
If you’ve recently powered on a VMware Virtual Machine (VM) only to be greeted by the message "Virtual device serial0 will start disconnected," you aren’t alone. While this warning might seem alarming, it’s usually a minor configuration mismatch rather than a sign of a failing system.
Here is a deep dive into why this happens and how you can fix it. Why Does This Message Appear?
In the world of virtualization, "Serial0" refers to a virtual serial (COM) port assigned to your VM. This error occurs because the VM is configured to look for a physical or virtual serial port on the host machine that either doesn't exist or is currently in use by another application. Common scenarios include: virtual device serial0 will start disconnected
Legacy Templates: You are using a VM template that originally had a serial port mapped for debugging.
Hardware Migration: You moved the VM from a host that had a physical COM port to one that doesn't.
Disconnected Peripherals: The VM is set to connect to a named pipe or a physical port that is disconnected. How to Fix the "Serial0" Warning
Depending on whether you actually need the serial port, there are two main ways to handle this. Method 1: Remove the Serial Port (Recommended)
Most modern users and operating systems do not require a serial port. Removing it is the cleanest way to stop the error message. Shut down the Virtual Machine.
Right-click the VM in your library and select Edit Settings. Locate Serial Port 1 (or Serial0) in the hardware list. Click the Remove or "X" icon. Click OK and power the VM back on.
The error message "Virtual device serial0 will start disconnected" typically occurs in The message "Virtual device serial0 will start disconnected"
environments and indicates that a virtual serial port cannot find its intended hardware or software backend during power-on
. This issue is most frequently tied to deprecated printing features or misconfigured virtual machine (VM) settings. Core Causes ThinPrint Deprecation : In recent versions like VMware Workstation 17.5 Fusion 13.5
, support for "ThinPrint" (a virtual printing technology) has been discontinued. VMs created in older versions often still have a serial port configured to use this driver, which now triggers the "invalid value" warning. Resource Conflicts
: The guest OS may be attempting to allocate the virtual device to a COM port that is already in use by the host system or another process. Licensing Restrictions
: In enterprise environments (ESXi), certain licenses do not permit the use of remote serial ports, causing the device to default to a disconnected state. Backend Connectivity
: If the serial port is configured to connect to a physical host port, a named pipe, or a specific file that is currently unavailable or inaccessible, the VM will power on with the device disconnected to prevent a full boot failure. Resolution Strategies Disable Virtual Printing : The most common fix is to navigate to Edit > Preferences > Devices in VMware Workstation and uncheck "Enable virtual printers" Modify VM Settings : Right-click the affected VM, go to , select the Serial Port device, and uncheck "Connect at power on"
. If the printer is not needed, you can remove the device entirely. Edit the .vmx File By internalizing this behavior, you stop fighting the
: For users of VMware Fusion or advanced users, manually editing the VM configuration ( ) file to remove entries like serial0.fileType = "thinprint" can permanently resolve the error. Advanced vCenter Configuration
: For persistent network-backed serial port issues in vSphere, adding the parameter vpxd.SerialPort.PersistNetworkBacking = "True"
in the vCenter Server's advanced settings can help maintain connections. Impact on Operations In most cases, this message is a non-critical warning
. Unless your workflow specifically requires a serial console or virtual printing, you can typically dismiss the message and the VM will function normally. for editing the file on your specific operating system? Virtualization Architect Technical Support Engineer
This warning message, "virtual device serial0 will start disconnected", is one of the most common errors seen by users of VMware Workstation, VMware Player, and VMware Fusion.
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.
Here is your complete guide to understanding, fixing, and silencing this message.
If the UI options do not fix the issue, you may need to edit the VM's configuration file directly.
serial0.fileName = "C:\VM\Logs\serial_output.txt"
(Note: Ensure the folder exists, or VMware will fail to connect).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.