LOSETUP(8) System Administration LOSETUP(8)NAMElosetup - 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 size]
[-p pfd] [-r] {-f[--show]|loopdev} file
Resize loop device:
losetup-c loopdev
DESCRIPTIONlosetup 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 corre‐
sponding loop device is shown.
Encryption
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.
OPTIONS
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 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
-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
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
-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 VALUElosetup returns 0 on success, nonzero on failure. When losetup displays
the status of a loop device, it returns 1 if the device is not config‐
ured and 2 if an error occurred which prevented losetup from determin‐
ing 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. 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
cryptsetup(8).
AVAILABILITY
The losetup command is part of the util-linux package and is available
from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
util-linux July 2003 LOSETUP(8)
