Section: System Administration (8)
Updated: July 2003
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losetup - set up and control loop devices
Print name of first unused loop device:
Setup loop device:
Resize loop device:
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.
It is possible to specify transfer functions (for encryption/decryption
or other purposes) using one of the
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.
The size and offset arguments may be followed by binary (2^N)
suffixes KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K" has the
same meaning as "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and EB.
- -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
argument is present, use this device. Otherwise, print its name
- -h, --help
- -j, --associated file
show status of all loop devices associated with given
- -k, --keybits num
set the number of bits to use in key to num.
- -N, --nohashpass
Do not hash the password. By default, Debian systems run the password through a
hash function, non-Debian systems tend not to.
- -o, --offset offset
the data start is moved offset bytes into the specified file or
- --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
instead of from the terminal
- -r, --read-only
setup read-only loop device
print device name if the
option and a
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
- -v, --verbose
returns 0 on success, nonzero on failure. When
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.
/dev/loop0, /dev/loop1, ... loop devices (major=7)
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
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
# rmmod loop
DES encryption is painfully slow. On the other hand, XOR is terribly weak.
Both are insecure nowadays. Some ciphers may require a licence for you to be
allowed to use them.
Cryptoloop is deprecated in favor of dm-crypt. For more details see
The losetup command is part of the util-linux package and is available from
- RETURN VALUE
This document was created by
using the manual pages.
Time: 07:05:20 GMT, January 20, 2018