Troubleshooting VMware: "Virtual device serial0 will start disconnected"
If you’ve recently powered on a VMware Workstation or ESXi virtual machine only to be greeted by the warning message "Virtual device serial0 will start disconnected," you aren’t alone. This is a common configuration hiccup that occurs when a VM is looking for a physical or virtual serial (COM) port that the host system can’t provide.
While it usually doesn’t prevent the guest OS from booting, it can be an annoying hurdle—especially if you need console access or simply want a clean, error-free startup. Why is this happening?
At its core, this error means the Virtual Machine settings include a Serial Port hardware device, but the "Backing" (the physical resource it’s supposed to connect to) is missing or busy. Common culprits include:
Missing Physical Ports: Your VM is configured to use "Physical Serial Port COM1," but your modern laptop doesn't actually have a 9-pin serial port.
Disconnected Pipes: The VM is set to use a "Named Pipe" for debugging, but the other end of the pipe isn't active.
Conflict: Another application or VM is already using the host's COM port.
Legacy Templates: You cloned a VM from an older template that included serial hardware by default. How to Fix "Serial0 Will Start Disconnected" virtual device serial0 will start disconnected
Depending on whether you actually need the serial port or just want the error to go away, use one of the following three methods. Method 1: Remove the Serial Port (Recommended)
Most modern operating systems (Windows 10/11, standard Linux distros) do not require a serial port to function. If you aren't doing low-level kernel debugging or connecting to industrial hardware, the easiest fix is to delete the device. Shut down the virtual machine. Right-click the VM and select Settings. Go to the Hardware tab. Locate Serial Port (or Serial0) in the list. Click Remove. Click OK and restart the VM. Method 2: Disconnect at Power On
If you think you might need the port later but want to stop the error message now, you can tell VMware to ignore it during boot. Go to VM Settings > Hardware. Select Serial Port.
Under the "Device status" section, uncheck Connect at power on.
This keeps the hardware in your configuration but prevents VMware from trying (and failing) to initialize it during startup. Method 3: Point to an Output File
If you are a developer or sysadmin who needs the data from that serial port, you can redirect the "Serial0" output to a text file on your host machine instead of a physical port. In VM Settings, select the Serial Port. Change the connection type to Output to file.
Browse to a location on your host and create a .txt or .log file. Configuration: The serial port might not be connected
Click Save. Now, anything the VM sends to the serial port will be recorded in that file without triggering a connection error. Still seeing the error?
If the error persists or the settings won't save, you may need to manually edit the VM's configuration file: Navigate to the folder where your VM is stored. Open the .vmx file with Notepad. Look for lines starting with serial0.
Change serial0.present = "TRUE" to serial0.present = "FALSE". Save the file and reload the VM in VMware.
The "virtual device serial0" error is rarely a "broken" VM; it’s just a mismatch between virtual hardware and physical reality. By removing the port or disabling the "Connect at power on" toggle, you can return to a seamless, one-click boot process.
Are you using this serial port for kernel debugging or just trying to get a clean boot?
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. but it is annoying.
Here is your complete guide to understanding, fixing, and silencing this message.
The message indicates that the virtual device associated with serial0 (the first virtual serial port in many virtualization platforms) is not connected when the VM starts up. This disconnection can occur for several reasons:
If you add a serial port to a VM but do not specify what it connects to (e.g., a physical COM port, a file, a named pipe, or an output to a printer), VMware will default to disconnecting it. The device is present but inactive.
dynagen):Add this to your .net file under [[defaults]]:
[[defaults]]
console = 2000
sparsemem = True
ghostios = True
# This does not suppress the message, but ensures faster boot
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.
To understand the fix, you must understand the hardware.
Is this dangerous? For 99% of modern users: No. Modern operating systems (Windows 10/11, modern Linux) and modern software do not use serial ports for anything critical. You can usually ignore this, but it is annoying.
