root@intel-corei7-64:~# umount /media/realroot/
umount: /media/realroot/: target is busy
        (In some cases useful info about processes that
         use the device is found by lsof(8) or fuser(1).)
root@intel-corei7-64:~# resize2fs /dev/sda
resize2fs 1.42.9 (28-Dec-2013)
resize2fs: Bad magic number in super-block while trying to open /dev/sda