Requisites:
You have a working installation of Oracle VirtualBox The directory you keep your virtual machines is $HOME/VM (our example) You have created a virtual machine called alpha (our example) that has no hard disk You have plugged in your USB stick and its device name is /dev/sdx (our example)
Objectives:
You want to install Linux on a USB flash drive from within VirtualBox OR: You want to boot a USB flash drive using VirtualBox
Once the above requisites are met, run the following in a terminal:
VboxManage internalcommands createrawvmdk -filename $HOME/VM/alpha/usbflash.vmdk -rawdisk /dev/sdx
Run the Oracle VM VirtualBox Manager, select the alpha virtual machine and go to its Storage properties, then select the hard disk controller and add the newly created disk usbflash.vmdk
Confirm all your changes and close the Storage properties.
Start the alpha virtual machine and you will find that your USB flash drive
now is attached as a hard disk that you can install Linux to, or boot from