If you are using the loadable module you must have the module loaded first with the command:

$ sudo modprobe loop

The following commands can be used as an example of using the loop device.

$ dd if=/dev/zero of=file bs=1k count=100100+0 records in100+0 records out102400 bytes (102 kB) copied, 0.00126554 s, 80.9 MB/s$ sudo losetup /dev/loop0 file$ sudo mkfs.ext3 /dev/loop0mke2fs 1.40.8 (13-Mar-2008)Filesystem label=OS type: LinuxBlock size=1024 (log=0)Fragment size=1024 (log=0)16 inodes, 100 blocks5 blocks (5.00%) reserved for the super userFirst data block=11 block group8192 blocks per group, 8192 fragments per group16 inodes per groupWriting inode tables: doneFilesystem too small for a journalWriting superblocks and filesystem accounting information: doneThis filesystem will be automatically checked every 24 mounts or180 days, whichever comes first.  Use tune2fs -c or -i to override.

mount loop device

$ sudo mkdir /mnt/loop$ sudo mount /dev/loop0 /mnt/loop

Now！ you can using it as harddisk.

umount loop device

$ sudo umount /mnt/loop/$ sudo losetup -d /dev/loop0

Maybe also encryption modules are needed.

$ sudo modprobe cryptoloop$ sudo modprobe des

enable data encryption

$ dd if=/dev/zero of=encryption_file bs=1k count=100100+0 records in100+0 records out102400 bytes (102 kB) copied, 0.00130537 s, 78.4 MB/s$ sudo losetup -e des /dev/loop0 encryption_file

If you are using the loadable module you may remove the module with the command

$ sudo rmmod loop des cryptoloop

If you are using the loadable module you must have the module loaded first with the command              # insmod loop.o       Maybe also encryption modules are needed.              # insmod des.o # insmod cryptoloop.o       The following commands can be used as an example of using the loop device.              # dd if=/dev/zero of=/file bs=1k count=100              # losetup -e des /dev/loop0 /file              Password:              Init (up to 16 hex digits):              # mkfs -t ext2 /dev/loop0 100              # mount -t ext2 /dev/loop0 /mnt               ...              # umount /dev/loop0              # losetup -d /dev/loop0       If you are using the loadable module you may remove the module with the command              # rmmod loop

原文出处：Netkiller 系列 手札