losetup

LOSETUP(8)                   MAINTENANCE COMMANDS                   LOSETUP(8)



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 limit]
                    [-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 corre‐
       sponding 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
       -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 limit
              the  data  end  is set to no more than sizelimit 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 config‐
       ured and 2 if an error occurred which prevented losetup from  determin‐
       ing 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-ng package and is avail‐
       able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.



Linux                             2003-07-01                        LOSETUP(8)