losetup — set up and control loop devices
losetup loopdev
losetup −a
losetup −j file [ −o offset ]
losetup −d loopdev...
losetup −f
losetup [
−e | −E encryption ] [ −o offset ] [ −−sizelimit limit ] [
−p pfd ]
[−r] −f [−−show] | loopdev
file
losetup −c loopdev
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.
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.
−a,
−−allshow status of all loop devices
−c,
−−set−capacity
loopdevforce 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_typeenable data encryption with specified name or number
−f,
−−findfind the first unused loop device. If a file argument is present,
use this device. Otherwise, print its name
−h,
−−helpprint help
−j,
−−associated fileshow status of all loop devices associated with
given file
−o,
−−offset offsetthe data start is moved offset bytes into the
specified file or device
−−sizelimit limitthe data end is set to no more than sizelimit bytes after the data start
−p,
−−pass−fd numread the passphrase from file descriptor with number
num instead
of from the terminal
−r,
−−read−onlysetup read-only loop device
−−showprint 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,
−−verboseverbose mode
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
# 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