virtualbox

USB-to-serial

To work with USB-to-serial adapters, such as the FTDI friend from Adafruit, add them to VirtualBox as USB devices, not serial ports. Adding these adapters as serial ports causes problems. For example, they might drop out after a disconnect and you would be forced to reboot the guest OS to detect the device again. Other methods, such as named pipes, seem unreliable.

To add an adapter as a USB device, go to machine Settings -> USB, click Enable USB Controller, then Add a Filter from Device. Note that the adapter should be connected at this time, otherwise, it will not be listed under the Add a Filter from Device menu.