LOSETUP linux command manual
LOSETUP(8) MAINTENANCE COMMANDS LOSETUP(8)
NAME
losetup - set up and control loop devices
SYNOPSIS
losetup [ [-e|-E] encryption ] [ -o offset ] [ -p pfd ] loop_device
file
losetup [ -d ] loop_device
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 loop_device argument is given, the status of the
corresponding loop device is shown.
Encryption
It is possible to specify transfer functions (for encryption/decryp-
tion 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 num-
ber, probably by patching the kernel. Standard numbers that are always
present are 0 (no encryption) and 1 (XOR encryption). When the cryp-
toloop module is loaded (or compiled in), it uses number 18. This
cryptoloop module wil take the name of an arbitrary encryption type
and finds the module that knows how to perform that encryption.
(Thus, either one uses a number different from 18 with the -E option,
or one uses a name with the -e option.)
OPTIONS
-d Detach the file or device associated with the specified loop
device.
-E encryption_type
Enable data encryption with specified number.
-e encryption_name
Enable data encryption with specified name.
-o offset
The data start is moved offset bytes into the specified file or
device.
-p num Read the passphrase from file descriptor with number num
instead of from the terminal.
RETURN VALUE
losetup returns 0 on success, nonzero on failure. When losetup dis-
plays 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
# insmod loop.o
Maybe also encryption modules are needed.
# insmod des.o # insmod cryptoloop.o
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.
Linux 2003-07-01 LOSETUP(8)