LOSETUP(8)

NAME
losetup - set up and control loop devices

SYNOPSIS
Get info:

losetup loopdev

losetup -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

Setup loop device:

losetup [{-e|-E} encryption] [-o offset] [--sizelimit size]
[-p pfd] [-rP] {-f[--show]|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.

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, PB, EB, ZB and YB.

-a, --all
    show status of all loop devices. Note that not all information are accessible for non-root users.

-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)

-D, --detach-all
    detach all associated loop devices

-e, -E, --encryption encryption_type
    enable data encryption with specified name or number

-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

-o, --offset offset
    the data start is moved offset bytes into the specified file or device

--sizelimit size
    the data end is set to no more than size bytes after the data start

-p, --pass-fd num
    read the passphrase from file descriptor with number num instead of from the terminal

-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 deprecated in favor of dm-crypt. For more details see cryptsetup (8). It is possible that all bug reports regarding to -E/-e options will be ignored. It is possible to specify transfer functions (for encryption/decryption or other purposes) using one of the -E and -e options. There are two mechanisms to specify the desired encryption: by number and by name. If an encryption is specified by number then one has to make sure that the Linux kernel knows about the encryption with that number, probably by patching the kernel. Standard numbers that are always present are 0 (no encryption) and 1 (XOR encryption). When the cryptoloop module is loaded (or compiled in), it uses number 18. This cryptoloop module will take the name of an arbitrary encryption type and find the module that knows how to perform that encryption.

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/.