scrub (1) Linux Manual Page

NAME

scrub – write patterns on disk/file

SYNOPSIS

scrub [OPTIONS] special-file [special-file …]
scrub [OPTIONS] file [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 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.

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: 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. 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 available.

-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.

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.

custom=string

1-pass custom pattern. String may contain C-style numerical escapes:
nn (octal) or