losetup man page on Gentoo

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LOSETUP(8)		     System Administration		    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...

       Delete all used loop devices:

	    losetup -D

       Print name of first unused loop device:

	    losetup -f

       Setup loop device:

	    losetup [{-e|-E} encryption] [-o offset] [--sizelimit size]
		    [-p pfd] [-rP] {-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 corre‐
       sponding loop device is shown.

OPTIONS
       +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

ENCRYPTION
       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.

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 config‐
       ured and 2 if an error occurred which prevented	from  determining  the
       status of the device.

FILES
       /dev/loop[0..N]
	      loop block devices

       /dev/loop-cotrol
	      loop control device

EXAMPLE
       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

AUTHORS
       Karel Zak <kzak@redhat.com>, based on original  version	from  Theodore
       Ts'o <tytso@athena.mit.edu>

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

util-linux			   July 2003			    LOSETUP(8)
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