losetup — set up and control loop devices
losetup
losetup −l [−a]
losetup −j file [ −o offset ]
losetup −d loopdev...
losetup −D
losetup [
−o offset ] [
−−sizelimit
size ] [ −−sector−size size
] [−Pr]
[−−show]
−f | loopdev
file
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 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.
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,
−−allShow 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−allDetach 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.
−−showDisplay the name of the assigned loop device if the
−f option and a
file argument
are present.
−L,
−−nooverlapCheck 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 offsetThe data start is moved offset bytes into the
specified file or device. The offset may be followed by
the multiplicative suffixes; see above.
−−sizelimit sizeThe 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 sizeSet 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 loopdevForce the loop driver to reread the size of the file associated with the specified loop device.
−P,
−−partscanForce 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−onlySet 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,
−−verboseVerbose mode.
−l,
−−listIf 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−allOutput all available columns.
−n,
−−noheadingsDon't print headings for −−list output format.
−−rawUse the raw −−list output format.
−J,
−−jsonUse JSON format for −−list output.
−V,
−−versionDisplay version information and exit.
−h,
−−helpDisplay 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.
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