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 scrub(1)                        scrub-2.6.1                        scrub(1)
 scrub                                                                 scrub


      scrub - write patterns on disk/file

      scrub [OPTIONS] special-file [special-file ...]
      scrub [OPTIONS] file [file ...]
      scrub -X [OPTIONS] directory

      Scrub iteratively writes patterns on files or disk devices to make
      retrieving the data more difficult. Scrub operates in one of three
      modes: 1) The special file corresponding to an entire disk is scrubbed
      and all data on it is destroyed.  This mode is selected if file is a
      character or block special file.  This is the most effective method.
      2) A regular file is scrubbed and only the data in the file (and
      optionally its name in the directory entry) is destroyed. The file
      size is rounded up to fill out the last file system block.  This mode
      is selected if file is a regular file. See CAVEATS below.  3)
      directory is created and filled with files until the file system is
      full, then the files are scrubbed as in 2). This mode is selected with
      the -X option.  See CAVEATS below.

      Scrub accepts the following options:

      -v, --version
           Print scrub version and exit.

      -r, --remove
           Remove the file after scrubbing.

      -p, --pattern PATTERN
           Select the patterns to write.  See SCRUB METHODS below.  The
           default, nnsa, is reasonable for sanitizing modern PRML/EPRML
           encoded disk devices.

      -b, --blocksize blocksize
           Perform read(2) and write(2) calls using the specified blocksize
           (in bytes). K, M, or G may be appended to the number to change
           the units to KiBytes, MiBytes, or GiBytes, respectively.
           Default: 4M.

      -f, --force
           Scrub even if target contains signature indicating it has already
           been scrubbed.

      -S, --no-signature
           Do not write scrub signature.  Later, scrub will not be able to
           ascertain if the disk has already been scrubbed.

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 scrub(1)                        scrub-2.6.1                        scrub(1)
 scrub                                                                 scrub


      -X, --freespace
           Create specified directory and fill it with files until write
           returns ENOSPC (file system full), then scrub the files as usual.
           The size of each file can be set with -s, otherwise it will be
           the maximum file size creatable given the user's file size limit
           or 1g if unlimited.

      -D, --dirent newname
           After scrubbing the file, scrub its name in the directory entry,
           then rename it to the new name. The scrub patterns used on the
           directory entry are constrained by the operating system and thus
           are not compliant with cited standards.  This option only works
           with a single target.

      -s, --device-size size
           Override the device size (in bytes). Without this option, scrub
           determines media capacity using OS-specific ioctl(2) calls.  K,
           M, or G may be appended to the number to change the units to
           KiBytes, MiBytes, or GiBytes, respectively.

      -L, --no-link
           If file is a symbolic link, do not scrub the link target.  Do
           remove it, however, if --remove is specified.

      -R, --no-hwrand
           Don't use a hardware random number generator even if one is

      -t, --no-threads
           Don't generate random data in parallel with I/O.

      -n, --dry-run
           Do everything but write to targets.

      -h, --help
           Print a summary of command line options on stderr.

      nnsa 4-pass NNSA Policy Letter NAP-14.1-C (XVI-8) for sanitizing
           removable and non-removable hard disks, which requires
           overwriting all locations with a pseudorandom pattern twice and
           then with a known pattern: random(x2), 0x00, verify.

      dod  4-pass DoD 5220.22-M section 8-306 procedure (d) for sanitizing
           removable and non-removable rigid disks which requires
           overwriting all addressable locations with a character, its
           complement, a random character, then verify.  NOTE: scrub
           performs the random pass first to make verification easier:
           random, 0x00, 0xff, verify.

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 scrub(1)                        scrub-2.6.1                        scrub(1)
 scrub                                                                 scrub


      bsi  9-pass method recommended by the German Center of Security in
           Information Technologies ( 0xff, 0xfe,
           0xfd, 0xfb, 0xf7, 0xef, 0xdf, 0xbf, 0x7f.

           The canonical 35-pass sequence described in Gutmann's paper cited

           7-pass method described by Bruce Schneier in "Applied
           Cryptography" (1996): 0x00, 0xff, random(x5)

           Roy Pfitzner's 7-random-pass method: random(x7).

           Roy Pfitzner's 33-random-pass method: random(x33).

           US Army AR380-19 method: 0x00, 0xff, random.  (Note: identical to
           DoD 522.22-M section 8-306 procedure (e) for sanitizing magnetic
           core memory).

           1-pass pattern: 0x00.

           1-pass pattern: 0xff.

           1-pass pattern: random(x1).

           2-pass pattern: random(x2).

      old  6-pass pre-version 1.7 scrub method: 0x00, 0xff, 0xaa, 0x00,
           0x55, verify.

           5-pass pattern: 0x00, 0xff, 0xaa, 0x55, verify.

           1-pass custom pattern.  String may contain C-style numerical
           escapes: \nnn (octal) or \xnn (hex).

      Scrub may be insufficient to thwart heroic efforts to recover data in
      an appropriately equipped lab.  If you need this level of protection,
      physical destruction is your best bet.

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 scrub(1)                        scrub-2.6.1                        scrub(1)
 scrub                                                                 scrub


      The effectiveness of scrubbing regular files through a file system
      will be limited by the OS and file system.  File systems that are
      known to be problematic are journaled, log structured, copy-on-write,
      versioned, and network file systems.  If in doubt, scrub the raw disk

      Scrubbing free blocks in a file system with the -X method is subject
      to the same caveats as scrubbing regular files, and in addition, is
      only useful to the extent the file system allows you to reallocate the
      target blocks as data blocks in a new file.  If in doubt, scrub the
      raw disk device.

      On MacOS X HFS file system, scrub attempts to overwrite a file's
      resource fork if it exists.  Although MacOS X claims it will support
      additional named forks in the future, scrub is only aware of the
      traditional data and resource forks.

      scrub cannot access disk blocks that have been spared out by the disk
      controller.  For SATA/PATA drives, the ATA "security erase" command
      built into the drive controller can do this.  Similarly, the ATA
      "enhanced security erase" can erase data on track edges and between
      tracks.  The DOS utility HDDERASE from the UCSD Center for Magnetic
      Recording Research can issue these commands, as can modern versions of
      Linux hdparm.  Unfortunately, the analogous SCSI command is optional
      according to T-10, and not widely implemented.

      To scrub a raw device /dev/sdf1 with default NNSA patterns:

           # scrub /dev/sdf1
           scrub: using NNSA NAP-14.1-C patterns
           scrub: please verify that device size below is correct!
           scrub: scrubbing /dev/sdf1 1995650048 bytes (~1GB)
           scrub: random  |................................................|
           scrub: random  |................................................|
           scrub: 0x00    |................................................|
           scrub: verify  |................................................|

      To scrub the file /tmp/scrubme with a sequence of 0xff 0xaa bytes:

           # scrub -p custom="\xff\xaa" /tmp/scrubme
           scrub: using Custom single-pass patterns
           scrub: scrubbing /tmp/scrubme 78319616 bytes (~74MB)
           scrub: 0xffaa  |................................................|

      Jim Garlick <> This work was produced at the

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 scrub(1)                        scrub-2.6.1                        scrub(1)
 scrub                                                                 scrub


      University of California, Lawrence Livermore National Laboratory under
      Contract No. W-7405-ENG-48 with the DOE.  Designated UCRL-CODE-2003-
      006, scrub is licensed under terms of the GNU General Public License.

      DoD 5220.22-M, "National Industrial Security Program Operating
      Manual", Chapter 8, 01/1995.  NNSA Policy Letter: NAP-14.1-C,
      "Clearing, Sanitizing, and Destroying Information System Storage
      Media, Memory Devices, and other Related Hardware", 05-02-08, page
      XVI-8.  "Secure Deletion of Data from Magnetic and Solid-State
      Memory", by Peter Gutmann, Sixth USENIX Security Symposium, San Jose,
      CA, July 22-25, 1996.  "Gutmann Method", Wikipedia,  Darik's boot and Nuke
      FAQ: "Tutorial on Disk
      Drive Data Sanitization", by Gordon Hugues and Tom Coughlin,
      "Guidelines for Media Sanitization", NIST special publication 800-88,
      Kissel et al, September, 2006.  shred(1), hdparm(8)

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