If you never resized the filesystem, then yes, it's an 8GB filesystem sitting in a 50GB container. Assuming it's an ext2/3/4 filesystem, you just need to run (as root) "resize2fs /dev/sda6" and the filesystem will be enlarged to fill its partition. You can do that online, with the system running and the fileystem mounted.
EDIT: Arrrgh! I mistyped "sda4" where I should have had "sda6". Fortunately, trying to resize sda4 would have failed, harmlessly.
Last edited by rknichols; 07-25-2014 at 10:26 AM.