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.
While this warning rarely causes a total system crash or prevents the guest operating system from booting, it adds unnecessary clutter to startup logs and can indicate underlying configuration mismatches. In enterprise environments, resolving these warnings is essential for maintaining clean logs and ensuring that automated monitoring scripts do not trigger false alarms.
Another application or another running virtual machine is currently using the host's physical serial port. How to Fix the Error
The resolution depends on your specific needs and configuration: virtual device serial0 will start disconnected
| Aspect | Effect | |--------|--------| | Boot time | Slightly faster (no connection setup) | | Error logs | No “failed to connect” errors at boot | | Serial console access | Requires manual connection | | Compatibility | Guest OS may need to handle carrier-detect wait |
. When the software starts, it tries to initialize the serial port formerly used for ThinPrint, fails because the driver is missing, and displays this warning. Root Cause In previous versions, used a virtual serial port (
Upgrading VMware Workstation, Fusion, or ESXi to a newer version often leaves behind outdated configuration entries. This is especially common when upgrading from Workstation 10 to 12 or from Fusion 12 to 13.5, where legacy features like ThinPrint or old serial port emulation settings are no longer supported. The upgrade process migrates the .vmx file, but deprecated options may remain, generating the warning with each startup. If you add a serial port to a
The VM configuration is mapped to a physical COM port (e.g., COM1) on the host machine, but the host machine lacks a physical serial port. This is incredibly common with modern servers and laptops that dropped legacy serial ports years ago.
VMware displays this message when a virtual serial port (COM port) is enabled in the VM configuration, but the physical host resources it points to are missing, disconnected, or busy. The most common triggers include:
After upgrading VMware products, review the VMX file for outdated settings. Deprecated features like ThinPrint leave behind orphaned entries that can cause persistent warning messages. When the software starts, it tries to initialize
Older enterprise software that relies on a serial connection for hardware dongles, automated machinery, or specialized modems will fail to function.
The “Virtual device serial0 will start disconnected” message is a common informational warning that appears in various VMware products. It is not an indication of VM corruption or permanent failure, but rather a notification that the VM’s virtual COM port was unable to establish a connection during startup.
Manually edit the .vmx file to point to the correct host port by changing the serial0.fileName to the specific port name, such as COM3 on Windows or /dev/tty.USA19H3d2P1.1 on Mac.
Open the [VM_Name].vmx file using a text editor like vi or Notepad++.
Here is your complete guide to understanding, fixing, and silencing this message.
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