losetup(8)
NAME
losetup - set up and control loop devices
SYNOPSIS
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
Print the name of the first unused loop device:
losetup -f
Set up a loop device:
losetup [-o offset] [--sizelimit 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'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 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.
-c, --set-capacity loopdev
Force the loop driver to reread the size of the file associated
with the specified loop device.
-d, --detach loopdev...
Detach the file or device associated with the specified loop
device(s).
-D, --detach-all
Detach all associated loop devices.
--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.
-f, --find
Find the first unused loop device. If a file argument is
present, use the found device as loop device. Otherwise, just
print its name.
-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
Show the status of all loop devices associated with the given
file.
-J, --json
Use JSON format for --list output.
-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 --json and --raw.
-n, --noheadings
Don't print headings for --list output format.
-o, --offset offset
The data start is moved offset bytes into the specified file or
device.
-O, --output columns
Specify the columns that are to be printed for the --list
output.
-P, --partscan
Force the kernel to scan the partition table on a newly created
loop device.
--raw Use the raw --list output format.
-r, --read-only
Set up a read-only loop device.
--sizelimit size
The data end is set to no more than size bytes after the data
start.
--show Display the name of the assigned loop device if the -f option
and a file argument are present.
-v, --verbose
Verbose mode.
-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.
FILES
/dev/loop[0..N]
loop block devices
/dev/loop-control
loop control device
EXAMPLE
The following commands can be used as an example of using the loop
device.
# dd if=/dev/zero of=~/file.img bs=1MiB 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
ENVIRONMENT
LOOPDEV_DEBUG=all
enables debug output.
AUTHORS
Karel Zak <kzak@redhat.com>, based on the original version from Theodore Ts'o <tytso@athena.mit.edu>
AVAILABILITY
The losetup command is part of the util-linux package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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