dd

Overwrite all partitions, the master boot record, and data:

dd if=/dev/zero of=/dev/sda bs=4M

This will overwrite everything with zeros (0).

Overwrite (more securely) all partitions, the master boot record, and data:

dd if=/dev/urandom of=/dev/sda bs=4M

This will overwrite everything with random data.

Progress check:

# to see the progress of dd enter:
kill -USR1 $(pidof dd)

Repeat to check again.

To wipe out your MBR:

dd if=/dev/zero of=/dev/hda bs=446 count=1

Wipe out MBR -AND- partition table:

dd if=/dev/zero of=/dev/hda bs=512 count=1

To create a copy or image of your hole disk or a partition, dd is quite useful because you can mount the image. With the image mounted you can browse and even copy files out of the image.

I used this to create a backup copy of my windows partition before reinstalling. I booted with the rescue CD from http://www.sysresccd.org and did the following steps:

# figure out the disk layout, identify your source partition and where it should go
fdisk -l 
 
# mount the ntfs data partition where the image will be placed:
mkdir /mnt/backup-drive
ntfs-3g /dev/sdc1 /mnt/backup-drive
 
# dd (using bs=16M gave me a throughput of 40 MB/sec)
dd if=/dev/sda2 of=/mnt/backup-drive/windows_c.img bs=16M
 
# Alt+F2 to the next console window, and run this command so see the 
# progress of dd in you Alt+F1 console window
while true; do sleep 5; kill -USR1 $(pidof dd); done

Mount the image to browse within:

mkdir /mnt/image_mount
mount -o loop /mnt/backup-drive/windows_c.img /mnt/image_mount