#!/bin/bash
## fill empty space with nulls to really delete everything

sfdisk -d /dev/sda \
| awk '/^.dev.sd/ {print $1}' \
| while read d; do
    mkdir -p /mnt/x
    mount $d /mnt/x
    ls -l /mnt/x
    echo "writing nulls to free space on $d ..."
    time cat /dev/zero > /mnt/x/zeroes
    sync
    rm /mnt/x/zeroes
    umount /mnt/x
  done
echo OK