How can I securely erase a hard drive?

Securely erasing a storage device

There's a command-line utility called shred, which overwrites data in a file or a whole device with random bits, making it nearly impossible to recover.

First of all, you need to identify the name of the device.

This might be something like /dev/sdb or /dev/hdb (but not like /dev/sdb1, that's a partition). You can use sudo fdisk -l to list all connected storage devices, and find your external hard drive there.

N.B. Make sure it is the correct device, picking the wrong device will wipe it.

Unmount all currently mounted partitions on that device, if any. Then run the following, replacing /dev/sdX with the name of your device:

sudo shred -v /dev/sdX

This will overwrite all the blocks on the device with random data three times, the -v flag is for verbose and will print the current progress.

You can add the option -nN to only do this N times, to save time on large capacity devices. This might take a while, depending on the size of your external hard drive (I think it takes twenty minutes or so for my 4 GB flash drive).

You can also set all bits to zero after the last iteration by adding the option -z, I prefer to do this.

sudo shred -v -n1 -z /dev/sdX

After this, you would have to repartition the device. The easiest way is to install GParted and use it:

sudo apt-get install gparted
gksu gparted

Choose your device in the upper-right corner list. Then select Device -> Create partition table to create a partition table on the device.

Then add a single partition that uses all of the unallocated space on the device, choosing fat32 as the file system. Apply the changes by click the Apply button (the green checkmark) in the toolbar.

Tips

• Read the manpage for shred online or by typing man shred in the terminal.
• Beware that some parts of your disk will not be erased - use the drive firmware "SECURE ERASE" command, such as via hdparm, to properly clean off a disk.

Just 'zero' it using the dd tool:

1. Start the Disk Utility via System > Administration > Disk Utility
2. Find your disk in the left panel, select it, and on the right find the device path (eg. /dev/sdX )
3. Run the following command from a terminal (Applications > Accessories > Terminal):
   
   sudo dd if=/dev/zero of=/dev/sdX bs=1M
   
   Make sure you use the right device path and not just copy this line!

This will overwrite the whole disk with zeros and is considerably faster than generating gigabytes of random data. Like all the other tools this won't take care of blocks that were mapped out for whatever reason (write errors, reserved, etc.), but it's highly unlikely your buyer will have the tools and the knowledge to recover anything from those blocks.

PS: Before you Bruce Schneier fanboys downvote me: I want proof that it's possible to recover data from a non-ancient rotational hard drive that has been overwritten with zeros. Don't even think about commenting otherwise! :P

I generally use a destructive read-write test using badblocks -w. The two major advantages are:

• it's part of the base system and almost every rescue system, so it is available e.g. from the rescue shell of the Ubuntu installer
• you get a report at the end whether there are bad blocks on the disk

Note that if the report indicates a problem, I'd no longer sell the disk as it is likely to fail soon.

Also Note: The -w does a 4-pass destructive write test by default.

Use write-mode test. With this option, badblocks scans for bad blocks by writing some patterns (0xaa, 0x55, 0xff, 0x00) on every block of the device, reading every block and comparing the contents.

Usage example (if your disk is sdd):

sudo badblocks -wsv /dev/sdd

(added sv for progress bar + verbose)

For a much faster wipe, add the -t option and do a single pass of zeros like so:

sudo badblocks -wsv -t 0x00 /dev/sdd

Have a look at this definitive question on Security Stack Exchange

How can I reliably erase all information on a hard drive

This discusses various secure deletion options, along with physical destruction and wiping so you can decide which option may be your best bet.

Remember though that the current recovery status for different storage is as follows:

• Very old hard drives: there were gaps between tracks so you could potentially pick up bleed into these gaps (if you had a scanning electron microscope handy). Overwriting multiple times was potentially useful.
• New hard drives: no technology currently exists that can read after even one overwrite.
• Solid state hard drives: wear levelling means you cannot overwrite securely. Instead you either encrypt the entire volume and dispose of the key to wipe, or you destroy the device.

Now, Disks (gnome-disks) tool has ATA Secure Erase. You may use it to erase your hard drive. Same option explained in this answer using the command-line tool hdparm.

WARNING!

Please, review disclaimer and warning notes at https://ata.wiki.kernel.org/index.php/ATA_Secure_Erase (Thanks to @colan to bring this up)

Also comments below. Some hardware may break.

1. Open Disks tool → Choose the target disk
2. From menu: Format Disk...
3. Select from drop box, Erase: ATA Enhanced Secure Erase ( if offered for the drive you selected ). Alternatively you can select Write zeros (slow) which can reasonably be considered to be secure.
4. Format

Best is to use the secure erase function of ATA drives. Secure erase erases the drive at firmware level. Can't get more secure.

First check if secure erase is supported:

sudo hdparm -I /dev/sdX | grep -i security

(replace sdX with sda/sdb/sdc, whatever your disk is).

If you see no output, just use dd:

sudo dd if=/dev/zero of=/dev/sdX bs=1M

If you see output, check if the device is not frozen:

sudo hdparm -I /dev/sdX | grep -i frozen

If it is frozen, see How to unfreeze drive in Linux? Otherwise if you see not frozen, set password to "Eins":

sudo hdparm --user-master u --security-set-pass Eins /dev/sdX

Optional: you might want to know how how long this will take:

sudo hdparm -I /dev/sdX | awk '/for SECURITY ERASE UNIT/'

Then execute the erase:

sudo hdparm --user-master u --security-erase Eins /dev/sdX

Then wait. Apparently for a 1TB disk this might take 3 hours or more.

There's a nice script which automated these steps.

• You need to create a loopback device which runs /dev/random over the entire contents of the drive.

• That'll fill the entire drive with almost completely random data.Then you can set all bits back to 0 with dd.

• Actually, dd should be able to randomize all of the information.

• You said that you have stored banking information on your harddisk.So i would suggest you to run any one of the following command from a live cd (where hdX is your harddrive).

  dd if=/dev/zero of=/dev/hdX

  dd if=/dev/random of=/dev/hdX

  dd if=/dev/urandom of=/dev/hdX

• How ever it will take a very long time based on your harddisk size.

For your information:

See the following links,

• Tools to delete files securely in ubuntu Linux
• Use an Ubuntu Live CD to Securely Wipe Your PC’s Hard Drive

Note:

• Random uses random bits and zero uses 0 bits.
• Urandom is a semi-random version of random.

you can use wipe

Installation

sudo apt-get install wipe

You can use that software or use the following command:

shred -vfz -n ? (drive)

Were the "?" is, put the number of times you wan to shred the drive, then for were "(drive)" is, put the drive that you want to shred. Once your done, do whatever you want with it. I think that this method is more effective since you can control what is done to your drive and have immediate results.

Links

1. http://wipe.sourceforge.net/
2. http://www.howtogeek.com/howto/15037/use-an-ubuntu-live-cd-to-securely-wipe-your-pcs-hard-drive/
3. http://ubuntuforums.org/showthread.php?t=817882

You can use DBAN. Wikipedia:

Darik's Boot and Nuke (commonly known as DBAN) [...] is designed to securely erase a hard disk until data is permanently removed and no longer recoverable, which is achieved by overwriting the data with random numbers generated by Mersenne twister or ISAAC (a PRNG). The Gutmann method, Quick Erase, DoD Short (3 passes), and DOD 5220.22-M (7 passes) are also included as options to handle Data remanence.

DBAN can be booted from a floppy disk, CD, DVD, or USB flash drive and it is based on Linux. It supports PATA (IDE), SCSI and SATA hard drives. DBAN can be configured to automatically wipe every hard disk that it sees on a system, making it very useful for unattended data destruction scenarios. DBAN exists for Intel x86 and PowerPC systems.

DBAN, like other methods of data erasure, is suitable for use prior to computer recycling for personal or commercial situations, such as donating or selling a computer[2]. In the case of malware infection, DBAN can be used before returning a disk to production.

One more advantage of shred over dd in this scenario: I have a faulty disk that I need to return to the vendor for an exchange.

dd halts at the first bad block, and fails to clobber the rest (unless I painfully use skip=... to jump ahead each time it stops).

shred ignores write errors and happily continues in this case.