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In some cases mostly on a Unix like host system (e.g. Mac OS & Linux distro.) . A USB Mass Storage Device in a guest OS is unavailable due to permission settings. Here is how to set-up your host OS to make the USB device available to your guest OS.

Let us configure a VirtualBox on a Mac OS X 10.6.4 Snow Leopard.
Now, open the VirtualBox application on a GUI or through the Terminal.

sudo open -a VirtualBox.app

Click on Settings->Ports and Click the USB icon with the plus sign to add a USB device.

Choose the USB you want to add. In this case we will add the JetFlash.
Note: make sure that the USB you want to add is connected.

Open a Terminal and enter this command to list all the USB Devices

VBoxManage list usbhost

In the terminal you will see a list of information about your USB devices.

The current state of the USB Mass Storage Device we want to access is unavailable.
To make it available we need a little configuration.
First is to add a user group named “vboxusers”
Open System Preperances->Accounts

Click on the plus sign icon, above the Lock icon to add new User/Group and the new account window will pop-up.
On New Account choose Group in the combo box.

Enter vboxusers in the Full Name Field.

A new group was added to your system.

Click on the vboxuser group and add members under that group.


Change the permission of the VirtualBox Drive.

sudo chgrp vboxusers /dev/vboxdrv
sudo chmod g+rw /dev/vboxdrv

Now let’s see the status of our the USB device.
EnterĀ VBoxManage list usbhost in terminal

VBoxManage list usbhost

You will notice that the state is still unavailable.

Now eject the USB and enter this command again.

VBoxManage list usbhost


The current state of the USB device is now “available”.
We can now access the host USB device into our guest OS.
Every time you will disconnect the USB in your guest OS it will be available to your host and vice-versa.