|
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | ENCRYPTION | EXIT STATUS | NOTES | ENVIRONMENT | FILES | EXAMPLE | AUTHORS | AVAILABILITY | COLOPHON |
|
|
|
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 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, --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. The offset 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. The size 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. 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-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 off.
-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'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.
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.
LOOPDEV_DEBUG=all
enables debug output.
/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
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
2020-12-18. (At that time, the date of the most recent commit
that was found in the repository was 2020-12-17.) 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)
|
HTML rendering created 2020-12-21 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|