losetup(8) — Linux manual page


LOSETUP(8)                  System Administration                 LOSETUP(8)

NAME         top

       losetup - set up and control loop devices

SYNOPSIS         top

       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         top

       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

       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.

OPTIONS         top

       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

       -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

       -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.

              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 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         top

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

EXIT STATUS         top

       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         top

              enables debug output.

FILES         top

              loop block devices

              loop control device

EXAMPLE         top

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

              # dd if=/dev/zero of=~/file.img bs=1024k count=10
              # losetup --find --show ~/file.img
              # mkfs -t ext2 /dev/loop0
              # mount /dev/loop0 /mnt
              # umount /dev/loop0
              # losetup --detach /dev/loop0

AUTHORS         top

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

AVAILABILITY         top

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

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found at 
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you have a
       bug report for this manual page, send it to
       util-linux@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2020-09-18.  (At that time, the date of the most recent commit that
       was found in the repository was 2020-09-15.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

util-linux                      November 2015                     LOSETUP(8)

Pages that refer to this page: loop(4)loop-control(4)mount(8)umount(8)