I am not able anymore to connect a VM to any of the host's COM ports under virtual box. I select "Host device" and tried typing "COM11" (Used to work in the past) "com11", "COM11:" or "com11:" but it always fails to boot with:

Failed to open host device 'COM11' (VERR_FILE_NOT_FOUND).
E_FAIL (0x80004005)
IConsole {872da645-4a9b-1727-bee2-5585105b9eed}

Any clues on how to solve it?

  • Host is a Windows 10 64bit machine.
  • Host has COM11 and COM12 at the time of VM boot
  • COM11 can be used by host applications (Putty et al)
  • Guest is DOS but since it doesn't even boot, is irrelevant.

2 Answers 2


The issue I was having is apparently using a port above COM9 requires special naming conventions. For COM1-COM9 you can just enter that into the Host path/address. COM11-COM256 need to be addressed by \\.\COM*

Source: https://www.virtualbox.org/ticket/6421


Apparently not all serial ports play nice. I noticed the FTDI based serial would work while de SiLabs based one wont.

Noticed an odd thing that may or may not be linked to this. Clicking on the advanced serial port options at the device properties if the window looks like this it doesnt work, but if it looks like this one it will.

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