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Linux 2.6 - man page for losetup (linux section 8)

LOSETUP(8)			       MAINTENANCE COMMANDS			       LOSETUP(8)

NAME
       losetup - set up and control loop devices

SYNOPSIS
       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 size]
		    [-p pfd] [-r] {-f[--show]|loopdev} file

       Resize loop device:

	    losetup -c loopdev

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  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.

OPTIONS
       The size and offset arguments may be followed by binary (2^N) suffixes KiB, MiB, GiB, TiB,
       PiB  and  EiB  (the  "iB"  is optional, e.g. "K" has the same meaning as "KiB") or decimal
       (10^N) suffixes KB, MB, GB, PB and EB.

       -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 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 termi-
	      nal

       -r, --read-only
	      setup read-only loop device

       --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 col-
	      lision with Loop-AES implementation where the same option is used for --sizelimit.

       -v, --verbose
	      verbose mode

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 com-
       mand

	      # 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

RESTRICTION
       DES encryption is painfully slow. On the other hand, XOR is terribly weak.  Both are inse-
       cure 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).

AVAILABILITY
       The losetup command is part of the util-linux package and is available from ftp://ftp.ker-
       nel.org/pub/linux/utils/util-linux/.

Linux					    2003-07-01				       LOSETUP(8)


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