redhat man page for losetup

LOSETUP(8)						       MAINTENANCE COMMANDS							LOSETUP(8)

NAME
       losetup - set up and control loop devices

SYNOPSIS
       losetup [ -e encryption ] [ -o offset ] loop_device file
       losetup [ -d ] loop_device

DESCRIPTION
       losetup	is  used  to  associate loop devices with regular files or block devices, to detach loop devices and to query the status of a loop
       device. If only the loop_device argument is given, the status of the corresponding loop device is shown.

OPTIONS
       -d     detach the file or device associated with the specified loop device.

       -e encryption
	      enable data encryption. The following keywords are recognized:

	      NONE   use no encryption (default).
	      XOR    use a simple XOR encryption.
	      DES    use DES encryption. DES encryption is only available if the optional DES package has been added to the kernel. DES encryption
		     uses an additional start value that is used to protect passwords against dictionary attacks.

       -o offset
	      the data start is moved offset bytes into the specified file or device.

RETURN VALUE
       losetup returns 0 on success, nonzero on failure. When losetup displays the status of a loop device, it returns 1 if the device is not con-
       figured and 2 if an error occurred which prevented losetup from determining the status of the device.

FILES
       /dev/loop0,/dev/loop1,...   loop devices (major=7)

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

	      # insmod loop.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

RESTRICTION
       DES encryption is painfully slow. On the other hand, XOR is terribly weak.

AUTHORS
       Original version: Theodore Ts'o <tytso@athena.mit.edu>
       Original DES by: Eric Young <eay@psych.psy.uq.oz.au>

Linux								    Nov 24 1993 							LOSETUP(8)