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...

Print name of first unused loop device:

losetup -f

Setup loop device:

losetup [{-e|-E} encryption] [-o offset] [--sizelimit limit]
[-p pfd] [-r] {-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¶

-a, --all

show status of all loop devices

-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)

-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 limit

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

-p, --pass-fd num

read the passphrase from file descriptor with number num instead of from the terminal

-r, --read-only

setup read-only loop device

--show

print device name if the -f option and a file argument are present.

The short form of this option (-s) is deprecated. This short form could be in collision with Loop-AES implementation where the same option is used for --sizelimit.

-v, --verbose

verbose mode

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 losetup from determining the status of the device.

FILES¶

/dev/loop0, /dev/loop1, ...   loop devices (major=7)

EXAMPLE¶

If you are using the loadable module you must have the module loaded first with the command

# modprobe loop

Maybe also encryption modules are needed.

# modprobe des # modprobe cryptoloop

The following commands can be used as an example of using the loop device.

# dd if=/dev/zero of=/file bs=1k count=100
# losetup -e des /dev/loop0 /file
Password:
Init (up to 16 hex digits):
# mkfs -t ext2 /dev/loop0 100
# mount -t ext2 /dev/loop0 /mnt


 ...
# umount /dev/loop0
# losetup -d /dev/loop0

If you are using the loadable module you may remove the module with the command

# rmmod loop

RESTRICTION¶

DES encryption is painfully slow. On the other hand, XOR is terribly weak.

Cryptoloop is deprecated in favor of dm-crypt. For more details see cryptsetup(8).

AVAILABILITY¶

The losetup command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.