LOSETUP(8)		     MAINTENANCE COMMANDS		   LOSETUP(8)



NAME
       losetup - set up and control loop devices

SYNOPSIS
       losetup [ [-e|-E] encryption ] [ -o offset ] [ -p pfd ] 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.


   Encryption
       It  is  possible to specify transfer functions (for encryption/decryp-
       tion 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 num-
       ber, probably by patching the kernel. Standard numbers that are always
       present	are 0 (no encryption) and 1 (XOR encryption).  When the cryp-
       toloop 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
       -d     Detach the file or device associated with	 the  specified	 loop
	      device.

       -E encryption_type
	      Enable data encryption with specified number.

       -e encryption_name
	      Enable data encryption with specified name.

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

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

RETURN VALUE
       losetup	returns	 0  on success, nonzero on failure. When losetup dis-
       plays the status of a loop device, it returns 1 if the device  is  not
       configured  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

       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.



Linux				  2003-07-01			   LOSETUP(8)

UNIX/Linux commands referenced on this page:

1. file
2. which
3. insmod
4. as
5. dd
6. mkfs
7. mount
8. umount
9. rmmod