LOSETUP

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Section: MAINTENANCE COMMANDS (8)
Updated: Nov 24 1993
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NAME

losetup - set up and control loop devices

SYNOPSIS

losetup [ -e encryption ] [ -o offset ] 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.

OPTIONS

-d

detach the file or device associated with the specified loop device.

-e encryption

enable data encryption. The following keywords are recognized:

NONE: use no encryption (default).
XOR: use a simple XOR encryption.
DES: use DES encryption. DES encryption is only available if the optional DES package has been added to the kernel. DES encryption uses an additional start value that is used to protect passwords against dictionary attacks.

-o offset

the data start is moved offset bytes into the specified file or device.

RETURN VALUE

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.

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

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.

AUTHORS

Original version: Theodore Ts'o <tytso@athena.mit.edu>
Original DES by: Eric Young <eay@psych.psy.uq.oz.au>

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