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 speci-
       fied 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  arbi-
       trary 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

       -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

       -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 collision with Loop-AES implementa-
              tion 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 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

RESTRICTION
       DES encryption is painfully slow. On the other hand, XOR is terribly weak.

       Cryptoloop is deprecated in favor of dm-crypt. For more details see cryptsetup(8).

AVAILABILITY
       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/.



Linux                                                      2003-07-01                                                 LOSETUP(8)