LOSETUP linux command manual

LOSETUP(8)                   MAINTENANCE COMMANDS                  LOSETUP(8)

       losetup - set up and control loop devices

       losetup [ [-e|-E] encryption ] [ -o offset ] [ -p pfd ] loop_device
       losetup [ -d ] loop_device

       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.

       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.)

       -d     Detach the file or device associated with  the  specified  loop

       -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

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

       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.

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

       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

              # dd if=/dev/zero of=/file bs=1k count=100
              # losetup -e des /dev/loop0 /file
              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

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

Linux                             2003-07-01                       LOSETUP(8)