writes patterns on magnetic media to thwart data recovery

 scrub iteratively writes patterns on files or disk devices to make retrieving
 the data more difficult.
 .
 scrub can write patterns direct to disk, destroying any file system (preferred
 method), or it can write patterns on files, or on file system free space.
 .
 scrub writes NNSA NAP-14.x, DoD 5220.22-M, BSI, 35-pass gutmann, or one of
 several other selectable pattern sequences.
 .
 scrub operates at the POSIX system call level, thus it is portable to a wide
 variety of hardware platforms. However, this means it cannot do certain things
 like manipulate spare blocks on disks, etc..