losetup(8) - phpMan

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LOSETUP(8)                   MAINTENANCE COMMANDS                   LOSETUP(8)

       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.

       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 per-
       form 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

       -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

       -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 implementation where the same option is used for

       -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

              # 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
              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.

       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

Linux                             2003-07-01                        LOSETUP(8)

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