Virtual Device Serial0 Will Start Disconnected Better May 2026

This warning message (or log entry) typically appears in VMware products (like VMware Workstation, Player, or ESXi). It indicates that the virtual machine is configured to have a serial port, but the host computer cannot connect to it—usually because the designated file or device path does not exist yet.

Here is a comprehensive guide on why this happens and how to resolve it.

3. Named Pipe or File Path is Invalid

If you configure the serial port to connect to a named pipe (used for debugging kernel-mode code or connecting two VMs) but the pipe name is wrong or the target application isn't listening, VMware will disconnect it at startup.

3. Scenario B: You DO NOT Need the Serial Port (Standard Users)

If you are just running a standard OS (Windows, Linux, macOS) and are not debugging kernel panics, you likely do not need this device. Removing it will clean up your logs and slightly improve boot speed. virtual device serial0 will start disconnected

Steps to Remove:

  1. Power off the Virtual Machine.
  2. Open VM > Settings.
  3. Select Serial Port (Serial0).
  4. Click Remove.
  5. Click OK and start the VM.

Result: The warning will disappear completely.

For VMware ESXi (via vSphere Web Client)

  1. Navigate to VM Settings.
  2. Under Virtual Hardware, expand Serial Port.
  3. Check Connect at power on.
  4. Set Mode to "Use output file" and point to a datastore path like [datastore1] /dev/null.
  5. Click OK.

To remove: Select the serial port and click Delete. This warning message (or log entry) typically appears

Overview

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

4. Scenario Specifics & Troubleshooting

Step 3: Change the Connection State

Option A: Remove the Serial Port (if unused)

  1. Select the serial port.
  2. Click Remove.
  3. Power on the VM. The warning should disappear.

Option B: Configure it to Connect at Power On Power off the Virtual Machine

If you want the port active but connected to nothing (to suppress the warning), you must trick VMware into thinking it has a valid backing:

  1. Select the serial port.
  2. Choose Output to file.
  3. Set file path to nul (Windows) or /dev/null (Linux/macOS).
  4. Check Connect at power on.
  5. Click OK.

The VM will now think it has a valid serial port and will not log the disconnected warning.

Option C: Use Named Pipe to Nowhere (Advanced)

  1. Select Output to named pipe.
  2. Enter a pipe name, e.g., \\.\pipe\fake_serial (Windows) or /tmp/fake_serial (Linux).
  3. Check Connect at power on.
  4. The pipe does not need a listener – VMware will keep it connected but idle.