GNU/Linux man pages
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GNU/Linux |
Debian 6.0.8(Squeeze) |
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losetup(8) |
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losetup − set up and control loop devices
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 limit]
[−p pfd] [−r] {−f[−−show]|loopdev} file
Resize loop device:
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.
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.
−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 limit
the data end is set to no more than sizelimit 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
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−−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
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.
/dev/loop0, /dev/loop1, ... loop devices (major=7)
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
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).
The losetup command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
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losetup(8) | |