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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENCRYPTION | RETURN VALUE | FILES | EXAMPLE | ENVIRONMENT | AUTHORS | AVAILABILITY | COLOPHON |
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LOSETUP(8) System Administration LOSETUP(8)
losetup - set up and control loop devices
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
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 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.
--sizelimit size
The data end is set to no more than size bytes after the data
start.
-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.
-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 on.
-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.
-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.
Cryptoloop is no longer supported in favor of dm-crypt. For more
details see cryptsetup(8).
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.
/dev/loop[0..N]
loop block devices
/dev/loop-control
loop control device
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
LOOPDEV_DEBUG=all
enables debug output.
Karel Zak <kzak@redhat.com>, based on the original version from
Theodore Ts'o <tytso@athena.mit.edu>
The losetup command is part of the util-linux package and is
available from https://www.kernel.org/pub/linux/utils/util-linux/.
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
2018-02-02. (At that time, the date of the most recent commit that
was found in the repository was 2018-02-01.) 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
man-pages@man7.org
util-linux November 2015 LOSETUP(8)
Pages that refer to this page: loop(4), mount(8), umount(8)
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