losetup — set up and control loop devices
losetup
loopdev
losetup
−a
losetup
−j
file [ −o
offset ]
losetup
−d
loopdev...
losetup
−D
losetup
−f
losetup
[
−e
| −E
encryption ] [ −o
offset ] [ −−sizelimit
size ] [
−p
pfd ]
[−rP
] −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.
+The size
and
offset
arguments may
be followed by the multiplicative +suffixes KiB=1024,
MiB=1024*1024, and so on for GiB, TiB, PiB, EiB, ZiB and YiB
+(the "iB" is optional, e.g. "K" has the same meaning as
"KiB") or the suffixes +KB=1000, MB=1000*1000, and so on for
GB, PB, EB, ZB and YB.
−a,
−−all
show status of all loop devices. Note that not all information are accessible for non-root users.
−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)
−D,
−−detach−all
detach all associated loop devices
−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
−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
−P,
−−partscan
force kernel to scan partition table on newly created loop device
−r,
−−read−only
setup read-only loop device
−−show
print device name if the −f
option and a
file
argument
are present.
−v,
−−verbose
verbose mode
Cryptoloop is deprecated in favor of dm-crypt. For more details see cryptsetup (8). It is possible that all bug reports regarding to -E/-e options will be ignored.
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.
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 from determining the status of the device.
The following commands can be used as an example of using the loop device.
# dd if=/dev/zero of=~/file.img bs=1MiB count=10 # losetup --find --show ~/file.img /dev/loop0 # mkfs -t ext2 /dev/loop0 # mount /dev/loop0 /mnt ... # umount /dev/loop0 # losetup --detach /dev/loop0