LOSETUP(8)		     MAINTENANCE COMMANDS		    LOSETUP(8)



NAME
       losetup - set up and control loop devices

SYNOPSIS
       Get info:

	    losetup loop_device

       Delete loop:

	    losetup -d loop_device

       Print name of first unused loop device:

	    losetup -f

       Setup loop device:

	    losetup [{-e|-E} encryption] [-o offset] [-p pfd]
		    {-f|loop_device} file

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.


   Encryption
       It is possible to specify transfer functions (for encryption/decryption
       or  other  purposes) using one of the -E and -e options.  There are two
       mechanisms to specify the desired encryption: by number and by name. If
       an encryption is specified by number then one has to make sure that the
       Linux kernel knows about the encryption with that number,  probably  by
       patching the kernel. Standard numbers that are always present are 0 (no
       encryption) and 1 (XOR encryption).   When  the	cryptoloop  module  is
       loaded (or compiled in), it uses number 18.  This cryptoloop module wil
       take the name of an arbitrary encryption type and finds the module that
       knows  how to perform that encryption.  (Thus, either one uses a number
       different from 18 with the -E option, or one uses a name  with  the  -e
       option.)

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

       -E encryption_type
	      Enable data encryption with specified number.

       --encryption, -e encryption
	      Enable data encryption with specified name.

       -f     Find the first  unused  loop  device.  If  a  file  argument  is
	      present, use this device. Otherwise, print its name.

       --nohashpass, -N
	      Do  not  hash  the password.  By default, Debian systems run the
	      password through a hash function, non-Debian  systems  tend  not
	      to.

       --offset, -o offset

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

       --pass-fd, -p num
	      Read the passphrase from file descriptor with number num instead
	      of from the terminal.

       --keybits, -k num
	      set the number of bits to use in key to num.

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  config
       ured  and 2 if an error occurred which prevented losetup from determin
       ing 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

       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


RESTRICTION
       DES  encryption	is  painfully slow. On the other hand, XOR is terribly
       weak.  Both are insecure nowadays. Some ciphers may require  a  licence
       for you to be allowed to use them.



Linux				  2003-07-01			    LOSETUP(8)