losetup — set up and control loop devices
losetup
loop_device
losetup −d loop_device
losetup −f
losetup [
−e | −E encryption ] [ −o offset ] [ −p pfd ] −f | loop_device file
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.
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 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.)
−dDetach the file or device associated with the specified loop device.
−E
encryption_typeEnable data encryption with specified number.
−e
encryption_nameEnable data encryption with specified name.
−fFind the first unused loop device. If a file argument is present,
use this device. Otherwise, print its name.
−o
offsetThe data start is moved offset bytes into the
specified file or device.
−p
numRead the passphrase from file descriptor with number
num instead
of from the terminal.
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.
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