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/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
       -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 termi-
              nal.

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 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  com-
       mand

              # 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)