shred — Overwrite/Delete a file securely.
Overwrite the specified file repeatedly and remove, in order to make it harder for even very expensive hardware probing to recover the data.
$ shred file — Repeatedly overwrite the file content with random data.
$ shred -v file — Show progress info.
$ shred -n 5 file — Overwrite 5 times instead of the default is 25.
$ shred -x file — Use exact file size. Don’t round off.
$ shred -z file — At the end of shred, overwrite the file with zeros.
$ shred -u file — Overwrite, Truncate and Remove the file.
Read: man shred