This nixCraft post explain how to erase hard disk
The secure removal of data is not as easy as you may think. When you
delete a file using the default commands of the operating system (for
example “rm” in Linux/BSD/MacOS/UNIX or “del” in DOS or emptying the
recycle bin in WINDOWS) the operating system does NOT delete the file,
the contents of the file remains on your hard disk. The only way to
make recovering of your sensitive data nearly impossible is to
overwrite (“wipe” or “shred”) the data with several defined patterns.
For erasing hard disk permanently, you can use the standard dd
command. However, I recommend using shred command or wipe command or
Warning: Check that the correct drive or partition has been targeted.
Wrong drive or partition target going to result into data loss . Under
no circumstances we can be help responsible for total or partial data
loss, so please be careful with disk names. YOU HAVE BEEN WARNED!
Erase disk permanently using a live Linux cd
First, download a knoppix Live Linux CD or SystemRescueCd
Next, burn a live cd and boot your laptop or desktop from live CD. You
can now wipe any disk including Windows, Linux, Mac OS X or Unix-like
1. How do I use the shred command?
Shred originally designed to delete file securely. It deletes a file
securely, first overwriting it to hide its contents. However, the same
command can be used to erase hard disk. For example, if your hard
drive named as /dev/sda, then type the following command:
# shred -n 5 -vz /dev/sda
-n 5: Overwrite 5 times instead of the default (25 times).
-v : Show progress.
-z : Add a final overwrite with zeros to hide shredding.
The command is same for IDE hard disk hda (PC/Windows first hard disk
connected to IDE) :
# shred -n 5 -vz /dev/hda
Note: Comment from @Gilles
Replace shred -n 5 by shred -n 1 or by cat /dev/zero. Multiple passes are not useful unless your hard disk uses 1980s technology.
In this example use shred and /dev/urandom as the source of random
# shred -v --random-source=/dev/urandom -n1 /dev/DISK/TO/DELETE
# shred -v --random-source=/dev/urandom -n1 /dev/sda
2. How to use the wipe command
You can use wipe command to delete any file including disks:
# wipe -D /path/to/file.doc
3. How to use the scrub command
You can use disk scrubbing program such as scrub. It overwrites hard
disks, files, and other devices with repeating patterns intended to
make recovering data from these devices more difficult. Although
physical destruction is unarguably the most reliable method of
destroying sensitive data, it is inconvenient and costly. For certain
classes of data, organizations may be willing to do the next best
thing which is scribble on all the bytes until retrieval would require
heroic efforts in a lab. The scrub implements several different
algorithms. The syntax is:
# scrub -p nnsa|dod|bsi|old|fastold|gutmann|random|random2 fileNameHere
To erase /dev/sda, enter:
# scrub -p dod /dev/sda
4. Use dd command to securely wipe disk
You can wipe a disk is done by writing new data over every single bit.
The dd command can be used as follows:
# dd if=/dev/urandom of=/dev/DISK/TO/WIPE bs=4096
Wipe a /dev/sda disk, enter:
# dd if=/dev/urandom of=/dev/sda bs=4096
5. How do I securely wipe drive/partition using a randomly-seeded AES cipher from OpenSSL?
You can use openssl and pv command to securely erase the disk too.
First, get the total /dev/sda disk size in bytes:
# blockdev --getsize64 /dev/sda
Next, type the following command to wipe a /dev/sda disk:
# openssl enc -aes-256-ctr -pass pass:"$(dd if=/dev/urandom bs=128 count=1 2>/dev/null | base64)" -nosalt </dev/zero | pv -bartpes
399717171200 | dd bs=64K of=/dev/sda
6. How to use badblocks command to securely wipe disk
The syntax is:
# badblocks -c BLOCK_SIZE_HERE -wsvf /dev/DISK/TO/WIPE
# badblocks -wsvf /dev/DISK/TO/WIPE
# badblocks -wsvf /dev/sda