NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENCRYPTION | RETURN VALUE | FILES | EXAMPLE | ENVIRONMENT | AUTHORS | AVAILABILITY | COLOPHON

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

       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         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
       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 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
              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.

       --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 on.

       -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.

       -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
              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         top

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

RETURN VALUE         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.

FILES         top

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

       /dev/loop-control
              loop control device

EXAMPLE         top

       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         top

       LOOPDEV_DEBUG=all
              enables debug output.

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 ftp://ftp.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
       2016-09-01.  If you discover any rendering problems in this HTML ver‐
       sion 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 man‐
       ual page), send a mail to man-pages@man7.org

util-linux                      November 2015                     LOSETUP(8)