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scrub(1)				      scrub					 scrub(1)

       scrub - write patterns on disk/file

       scrub [OPTIONS] special-file
       scrub [OPTIONS] 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 rea-
	      sonable 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.

       -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.

       -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 num-
	      ber 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 available.

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

       -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.

       bsi    9-pass method recommended by the German Center of Security in Information Technolo-
	      gies  (http://www.bsi.bund.de):  0xff,  0xfe,  0xfd,  0xfb, 0xf7, 0xef, 0xdf, 0xbf,

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

	      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).

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

	      1-pass pattern: 0x00.

       fillff 1-pass pattern: 0xff.

       random 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

       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 device.

       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 <garlick@llnl.gov>

       This work was produced at the University of California, Lawrence Livermore National  Labo-
       ratory  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,

       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, http://en.wikipedia.org/wiki/Gutmann_method.

       Darik's boot and Nuke FAQ: http://dban.sourceforge.net/faq/index.html

       "Tutorial on Disk Drive Data Sanitization", by Gordon Hugues and Tom Coughlin,

       "Guidelines  for  Media Sanitization", NIST special publication 800-88, Kissel et al, Sep-
       tember, 2006.

       shred(1), hdparm(8)

scrub-2.5.2				    2012-06-20					 scrub(1)
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