NAME

losetup - set up and control loop devices

SYNOPSIS

Get info:

losetup loopdev

losetup -l [-a]

losetup -j file [-o offset]

Delete loop:

losetup -d loopdev...

Delete all used loop devices:

losetup -D

Print name of first unused loop device:

losetup -f

Set up a loop device:

losetup [-o offset] [--sizelimit size]
[-Pr] [--show] -f|loopdev file

Resize 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.

Note that the old output format (e.g. losetup -a) with comma delimited strings is deprecated in favour of the --list output format (e.g. losetup -a -l).

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 status of all loop devices. Note that not all information are accessible for non-root users. See also --list. The old output format (as printed without --list) is deprecated.
-c, --set-capacity loopdev: force loop driver to reread 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). 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: find the first unused loop device. If a file argument is present, use this device. Otherwise, print its name
-h, --help: print help
-j, --associated file: show status of all loop devices associated with given file
-l, --list: if a loop device or the -a option is specified, print default columns for either the specified loop device or all loop devices, default is to print info about all devices.
-o, --offset offset: the data start is moved offset bytes into the specified file or device
-O, --output columns: specify which columns are to be printed for the --list output
--sizelimit size: the data end is set to no more than size bytes after the data start
-P, --partscan: force kernel to scan partition table on newly created loop device
-r, --read-only: setup read-only loop device
--show: print device name if the -f option and a file argument are present.
-v, --verbose: verbose mode

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 from determining the status of the device.

FILES

/dev/loop[0..N]: loop block devices
/dev/loop-cotrol: 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

AUTHORS

Karel Zak <kzak@redhat.com>, based on 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/.