losetup <root
LOSETUP(8)                            System Administration                            LOSETUP(8)

NAME
       losetup - set up and control loop devices

SYNOPSIS
       Get info:

            losetup loopdev

            losetup -l [-a]

            losetup -j file [-o offset]

       Detach a loop device:

            losetup -d loopdev...

       Detach all associated loop devices:

            losetup -D

       Print the name of the first unused loop device:

            losetup -f

       Set up a loop device:

            losetup [-o offset] [--sizelimit size]
                    [-Pr] [--show] -f|loopdev file

       Resize a 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.  If no option is given, all
       loop devices are shown.

       Note that the old output format (i.e. losetup -a) with comma-delimited strings  is  depre‐
       cated in favour of the --list output format.

OPTIONS
       The  size and offset arguments may be followed by the multiplicative suffixes KiB (=1024),
       MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB  (the  "iB"  is  optional,
       e.g.,  "K" has the same meaning as "KiB") or the suffixes KB (=1000), MB (=1000*1000), and
       so on for GB, TB, PB, EB, ZB and YB.

       -a, --all
              Show the status of all loop devices.  Note that not all information  is  accessible
              for  non-root  users.   See also --list.  The old output format (as printed without
              --list) is deprecated.

       -c, --set-capacity loopdev
              Force the loop driver to reread the 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).

       -D, --detach-all
              Detach all associated loop devices.

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

       -j, --associated file
              Show the status of all loop devices associated with the given file.

       -J, --json
              Use JSON format for --list output.

       -l, --list
              If a loop device or the -a option is  specified,  print  the  default  columns  for
              either  the specified loop device or all loop devices; the default is to print info
              about all devices.  See also --output, --noheadings --json and --raw.

       -n, --noheadings
              Don't print headings for --list output format.

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

       -O, --output columns
              Specify the columns that are to be printed for the --list output.

       -P, --partscan
              Force the kernel to scan the partition table on a newly created loop device.

       --raw  Use the raw --list output format.

       -r, --read-only
              Set up a read-only loop device.

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

       --show Display the name of the assigned loop device if the -f option and a  file  argument
              are present.

       -v, --verbose
              Verbose mode.

       -V, --version
              Display version information and exit.

       -h, --help
              Display help text and exit.

ENCRYPTION
       Cryptoloop  is  no longer supported in favor of dm-crypt.  For more details see cryptsetup
       (8).

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 determining the status of the device.

FILES
       /dev/loop[0..N]
              loop block devices

       /dev/loop-control
              loop control device

EXAMPLE
       The following commands can be used as an example of using the loop device.

              # dd if=/dev/zero of=~/file.img bs=1MiB count=10
              # losetup --find --show ~/file.img
              /dev/loop0
              # mkfs -t ext2 /dev/loop0
              # mount /dev/loop0 /mnt
               ...
              # umount /dev/loop0
              # losetup --detach /dev/loop0

ENVIRONMENT
       LOOPDEV_DEBUG=all
              enables debug output.

AUTHORS
       Karel  Zak  ,  based  on  the  original  version   from   Theodore   Ts'o
       

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

util-linux                                  July 2014                                  LOSETUP(8)

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