NAME
losetup - set up and control loop devices
SYNOPSIS
Get info:
losetup [loopdev]
losetup-l [-a]
losetup-jfile [-ooffset]
Detach a loop device:
losetup-dloopdev ...
Detach all associated loop devices:
losetup-D
Set up a loop device:
losetup [-ooffset] [--sizelimitsize] [--sector-sizesize] [--loop-refname] [-Pr] [--show] -f|loopdev file
Resize a loop device:
losetup-cloopdev
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
-d, --detachloopdev...
-D, --detach-all
-f, --find [file]
--show
-L, --nooverlap
-j, --associatedfile [-ooffset]
-o, --offsetoffset
--loop-refstring
--sizelimitsize
-b, --sector-sizesize
-c, --set-capacityloopdev
-P, --partscan
-r, --read-only
--direct-io[=on|off]
-v, --verbose
-l, --list
-O, --outputcolumn[,column]...
--output-all
-n, --noheadings
--raw
-J, --json
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.
NOTES
Since version 2.37 losetup uses LOOP_CONFIGURE ioctl to setup a new loop device by one ioctl call. The old versions use LOOP_SET_FD and LOOP_SET_STATUS64 ioctls to do the same.
ENVIRONMENT
LOOPDEV_DEBUG=all
FILES
/dev/loop[0..N]
/dev/loop-control
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/loop0AUTHORS
Karel Zak <[email protected]>, based on the original version from Theodore Ts’o <[email protected]>.
REPORTING BUGS
For bug reports, use the issue tracker <https://github.com/util-linux/util-linux/issues>.
AVAILABILITY
The losetup command is part of the util-linux package which can be downloaded from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils/util-linux/>.