Update and upgrade the Raspbian installation.
sudo apt-get update && sudo apt-get upgrade
Install the package necessary to automatically mount USB drives.
sudo apt-get install usbmount
Now plug a USB drive and issue the df command to view all volumes. My USB drive was recognized /dev/sdb and mounted as /media/usb0 by the system.
To un-mount a volume make use of the df command above to discover the USB drive mount point and issue the unmount command as follows.
sudo umount /media/usb0