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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

       Set up a loop device:

            losetup [-o offset] [--sizelimit size] [--sector-size 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
       deprecated in favour of the --list output format.

       It's  possible  to  create  more independent loop devices for the same backing file.  This
       setup may be dangerous, can cause data loss, corruption and overwrites.   Use  --nooverlap
       with --find during setup to avoid this problem.

       The  loop  device setup is not an atomic operation when used with --find, and losetup does
       not protect this operation by any lock.  The number of attempts is  internally  restricted
       to a maximum of 16.  It is recommended to use for example flock(1) to avoid a collision in
       heavily parallel use cases.

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.

       -d, --detach loopdev...
              Detach  the  file or device associated with the specified loop device(s). Note that
              since Linux v3.7 kernel uses "lazy device destruction".  The detach operation  does
              not  return  EBUSY  error  anymore  if device is actively used by system, but it is
              marked by autoclear flag and destroyed later.

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

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

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

       -L, --nooverlap
              Check for conflicts between loop devices to avoid situation when the  same  backing
              file  is  shared  between more loop devices. If the file is already used by another
              device then re-use the device rather than a new one. The option  makes  sense  only
              with --find.

       -j, --associated file [-o offset]
              Show the status of all loop devices associated with the given file.

       -o, --offset offset
              The data start is moved offset bytes into the specified file or device.  The offset
              may be followed by the multiplicative suffixes; see above.

       --sizelimit size
              The data end is set to no more than size bytes after the data start.  The size  may
              be followed by the multiplicative suffixes; see above.

       -b, --sector-size size
              Set  the  logical  sector  size of the loop device in bytes (since Linux 4.14). The
              option may be used when create a new loop device as well as stand-alone command  to
              modify sector size of the already existing loop device.

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

       -P, --partscan
              Force the kernel to scan the partition table on a newly created loop device.   Note
              that  the  partition  table parsing depends on sector sizes.  The default is sector
              size is 512 bytes, otherwise you need to use the option --sector-size together with
              --partscan.

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

       --direct-io[=on|off]
              Enable  or  disable  direct I/O for the backing file.  The optional argument can be
              either on or off.  If the argument is omitted, it defaults to off.

       -v, --verbose
              Verbose mode.

       -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, --raw, and --json.

       -O, --output column[,column]...
              Specify the columns that are to be printed for the --list output.   Use  --help  to
              get a list of all supported columns.

       --output-all
              Output all available columns.

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

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

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

       -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).

EXIT STATUS

       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.

ENVIRONMENT

       LOOPDEV_DEBUG=all
              enables debug output.

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=1024k 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

AUTHORS

       Karel  Zak  <kzak@redhat.com>,  based  on  the  original  version   from   Theodore   Ts'o
       <tytso@athena.mit.edu>

AVAILABILITY

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