== THE LOOP DEVICE also called LOOPBACK DEVICE==
One further possible type is a mount via the loop device. For example, the command
- mount /tmp/fdimage /mnt -t msdos -o loop=/dev/loop3,blocksize=1024
will set up the loop device /dev/loop3 to correspond to the file /tmp/fdimage, and then mount this device on /mnt.
This type of mount knows about three options, namely loop, offset and encryption, that are really options to losetup(8). (These options can be used in addition to those specific to the filesystem type.)
If no explicit loop device is mentioned (but just an option `-o loop' is given), then mount will try to find some unused loop device and use that. If you are not so unwise as to make /etc/mtab a symbolic link to /proc/mounts then any loop device allocated by mount will be freed by umount.
You can also free a loop device by hand, using `losetup -d', see losetup(8).