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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.

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.
-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.
-j, --associated file
Show the status of all loop devices associated with the given file.
-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 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/loop0Authors

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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