scrub(1)							       scrub								  scrub(1)

NAME

       scrub - write patterns on disk/file

SYNOPSIS

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

DESCRIPTION

       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  char-
       acter 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.

OPTIONS

       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: 1M.

       -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
	      umlimited.

       -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 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.

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

SCRUB METHODS

       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 Technologies (http://www.bsi.bund.de): 0xff,  0xfe,  0xfd,
	      0xfb, 0xf7, 0xef, 0xdf, 0xbf, 0x7f.

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

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

       pfitzner7
	      Roy Pfitzner's 7-random-pass method: random(x7).

       pfitzner33
	      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 section 8-306 procedure (e) for sanitizing magnetic
	      core memory).

       fillzero
	      1-pass pattern: 0x00.

       fillff 1-pass pattern: 0xff.

       random 1-pass pattern: random(x1).

       random2
	      2-pass pattern: random(x2).

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

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

CAVEATS

       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.

       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 addi-
       tional 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 "enahanced security erase" can erase data on track edges and between
       tracks.	The DOS utility HDDERASE from from the UCSD Center for Magnetic Recording Research can issue these commands, as  can  modern  ver-
       sions of Linux hdparm.  Unfortunately, the analagous SCSI command is optional according to T-10, and not widely implemented.

AUTHOR

       Jim Garlick <garlick@llnl.gov>

       This  work  was	produced at the 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.

SEE ALSO

       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, 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,
       http://cmrr.ucsd.edu/people/Hughes/DataSanitizationTutorial.pdf.

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

       shred(1), hdparm(8)

scrub-2.4.1							    2011-08-29								  scrub(1)