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/.