root@giorgos-desktop:/home/giorgos# mount -o gid=6 /dev/sdf1 /media/usb
$LogFile indicates unclean shutdown (0, 0)
Failed to mount '/dev/sdf1': Operation not supported
Mount is denied because NTFS is marked to be in use. Choose one action:

Choice 1: If you have Windows then disconnect the external devices by
          clicking on the 'Safely Remove Hardware' icon in the Windows
          taskbar then shutdown Windows cleanly.

Choice 2: If you don't have Windows then you can use the 'force' option for
          your own responsibility. For example type on the command line:

            mount -t ntfs-3g /dev/sdf1 /media/usb -o force

    Or add the option to the relevant row in the /etc/fstab file:

            /dev/sdf1 /media/usb ntfs-3g defaults,force 0 0
root@giorgos-desktop:/home/giorgos#