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. virtual device serial0 will start disconnected

Under the "Device status" section, uncheck . A: The same rule applies

is set to "thinprint" incorrectly. You can often resolve this by following the VMware Knowledge Base Article 95329 or manually editing the file to ensure serial0.present = "FALSE" if you don't need the port [ For VMware ESXi/vSphere Users: Check Licensing: Instead, it starts the VM with that device

However, understanding why this message appears, what it actually means for your virtual lab, and how to resolve the underlying connectivity issue is crucial for building functional network topologies. This article provides a deep dive into the causes, step-by-step troubleshooting, and permanent solutions for the "Virtual device serial0 will start disconnected" message.