Section (8) losetup
Name
losetup — set up and control loop devices
Synopsis
- Get info:
-
losetup
- [fIloopdevfP]
-
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
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_zsingle_quotesz_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
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 afile
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. Theoffset
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. Thesize
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.
−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. −−output−all
-
Output all available columns.
−n, −−noheadings
-
Don_zsingle_quotesz_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
Cryptoloop is no longer supported in favor of dm-crypt. For more details see cryptsetup(8).
RETURN VALUE
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.
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/loop0
AUTHORS
Karel Zak <[email protected]>, based on the original version from Theodore Ts_zsingle_quotesz_o <[email protected]>