2021-06-09 update

https://askubuntu.com/questions/17640/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.

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How Do I Permanently Delete Files From My Hard Disk? | PCWorld

How Do I Permanently Delete Files From My Hard Disk?

Follow these simple instructions to completely remove files from your drive.

By Michael King, PCWorld    Nov 1, 2010 4:10 pm

Did you know that when you "delete" files from your computer, they can still remain on your hard disk? In many cases, deleted files can be recovered with little effort because most computer operating systems will only delete links to the data so they no longer appear to you, but the actual data remains on the disk. Getting access to the deleted data is as simple as restoring the links.

This method of deletion is fine for most circumstances--where security is not an issue--but you wouldn't want some people to recover your financial statements or medical records. For sensitive data, you need to make sure that your computer overwrites both the links to the information and the information itself.

Step-by-Step: Using Eraser

To make sure a file is truly gone, a number of tools are available. Eraser is a free and easy-to-use solution that will overwrite your private information with random patterns until the data is no longer recoverable. It works with nearly every version of Windows and offers a number of methods of overwriting your data, including methods approved by the Department of Defense.

Once installed, Eraser integrates nicely into Windows. Whenever you want to securely erase your data, follow these steps.

1. Navigate to the files or folders that you want to securely erase.

2. Right-click on the files and/or folders and an Eraser menu will appear.

3. Highlight and click Erase in the Eraser menu.

Eraser will automatically create the secure erase task and execute it immediately. You will be notified in a popup window when the task is complete and the files are permanently erased.

Eraser has a number of settings and options that you can configure, including securely deleting recycle bin contents and scheduling and automating secure deletion tasks.

Step-by-Step: Using SDelete

For users who don't need graphical interfaces, Microsoft has a downloadable command-line tool called SDelete. Here's how to use this tool.

1. Click Start > Run... , type cmd and press OK or Enter (Return). (Windows Vista and Windows 7 users can just click Start and type cmd in the Windows Search box.)

2. Navigate to where you have SDelete downloaded. For example, if it's located at C:\cmdtools, typecd C:\cmdtools, and press Enter.

3. Now type sdelete <path to file or directory>, and press Enter, where <path to file or directory> is a standard Windows path. For example, to delete C:\mysecuredata.txt, you would type sdelete c:\mysecuredata.txt, and press Enter.

4. Once they're deleted, you will receive confirmation that your files or folders have been permanently deleted, and you're done!

Now that you have the right tools for the job, you can feel confident in knowing that your data has actually been removed from your hard disk and will no longer be recovered by anyone (not even by you).

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