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NAME

       losetup - set up and control loop devices

SYNOPSIS

       Get info:

            losetup loopdev

            losetup -a

            losetup -j file [-o offset]

       Delete loop:

            losetup -d loopdev...

       Print name of first unused loop device:

            losetup -f

       Setup loop device:

            losetup [{-e|-E} encryption] [-o offset] [--sizelimit size]
                    [-p pfd] [-r] {-f[--show]|loopdev} file

       Resize loop device:

            losetup -c loopdev

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  loopdev  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
       will take the name of an arbitrary encryption type and find the  module
       that knows how to perform that encryption.

OPTIONS

       The  size and offset arguments may be followed by binary (2^N) suffixes
       KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K" has the
       same  meaning  as  "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and
       EB.

       -a, --all
              show status of all loop devices

       -c, --set-capacity loopdev
              force loop driver to reread size of the file associated with the
              specified loop device

       -d, --detach loopdev...
              detach  the  file  or  device associated with the specified loop
              device(s)

       -e, -E, --encryption encryption_type
              enable data encryption with specified name or number

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

       -h, --help
              print help

       -j, --associated file
              show status of all loop devices associated with given file

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

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

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

       --sizelimit size
              the data end is set to no more than size bytes  after  the  data
              start

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

       -r, --read-only
              setup read-only loop device

       --show print device name if the -f  option  and  a  file  argument  are
              present.

              The  short  form  of this option (-s) is deprecated.  This short
              form could be in collision with  Loop-AES  implementation  where
              the same option is used for --sizelimit.

       -v, --verbose
              verbose mode

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 command

              # modprobe loop

       Maybe also encryption modules are needed.

              # modprobe des # modprobe cryptoloop

       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.

       Cryptoloop  is  deprecated  in  favor of dm-crypt. For more details see
       cryptsetup(8).

AVAILABILITY

       The losetup command is part of the util-linux package and is  available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.