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.
3. A file is created, expanded until the file system is full, then scrubbed as
   in item 2. This mode is selected with the -X option.

Scrub implements user-selectable pattern algorithms that are compliant with
DoD 5520.22-M or NNSA NAP-14.x.

WWW: https://computing.llnl.gov/linux/scrub.html