Erasing a Linux laptop

I have a laptop with Debian on it, and I am going to sell this laptop.

Would it suffice to erase the Debian installation before selling it to completely clean up my laptop from my personal data, and if yes how can I uninstall Debian (so that there isn’t any operating system on the laptop)?

Answers:

Thank you for visiting the Q&A section on Magenaut. Please note that all the answers may not help you solve the issue immediately. So please treat them as advisements. If you found the post helpful (or not), leave a comment & I’ll get back to you as soon as possible.

Method 1

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
scrub command.

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
live CD.

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
system.

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

Where,

-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
data:

# 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
399717171200

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

Method 2

Boot your laptop from USB/CD and use DBAN: https://dban.org/

Regards.

Method 3

I’m going to suggest considering an alternative to wiping the drive.

Wiping the drive is dangerous in that you can lose data permanently. Additionally, depending on how worried you are about someone taking the data, it can be difficult to ensure that some drives are truly non-recoverable (e.g. SSDs that have internal mechanisms that spread writes around).

A simple and 100% effective solution is to just replace the drive with a new one. Keep the drive for yourself, and then you don’t even have to worry about it (barring someone breaking into your home or the computer to which it’s attached getting compromised). Whether this is worth your money is something only you can determine, but it’s a lot less hassle. As a bonus, now you have an extra drive for yourself. Make your decision by weighing the costs vs. the risk of attacks you wish to protect against.

Method 4

I would advise cleaning the disk doing it with:

sudo dd if=/dev/urandom of=/dev/sda bs=4M oflag=direct

I suggest /dev/urandom against /dev/zero especially if dealing with an SSD drive. You can use /dev/zero in mechanical disks, however supposedly using random values instead also adds more noise to a possible act of advanced recovery (not likely to happen, but has to be said).

dd is also more efficient (and faster) than the alternatives proposed here, namely doing a cat.

In addition, this method does not require you to boot from additional media, and dd is present by default in Linux.

Also be careful how you employ this command, as there is no recovery from it. Word of caution, double or triple check if it is the intended device (or even disconnect any external backup drives), as it is very easy to wipe out the wrong device for good by mistake.

Method 5

Login as root:

cat /dev/zero > /dev/sda

There is no need to do it more than once with a harddisk. If you have an old 8″ floppy it might be a good idea to erase a few times.

Method 6

If you happen to have a Self-Encrypting Drive (most modern HDDs and virtually all SSDs are also SEDs) and there’s nothing on the drive worth several $10000 of advanced data recovery services, you can use secure disk erase:

Whole disk erasure is very fast, and remarkably simple for a SED. Simply passing a cryptographic disk erasure (or crypto erase) command (after providing the correct authentication credentials) will have the drive self-generate a new random encryption key (DEK) internally. This will permanently discard the old key, thus rendering the encrypted data irrevocably un-decryptable.

The process is described here in details. Typically, you simply need to run two commands:

hdparm --user-master u --security-set-pass your_password /dev/X
hdparm --user-master u --security-erase your_password /dev/X

Of course, data recovery may still be possible, since HDD manufacturers tend to keep track of which key was used on which HDD, meaning they will also be able to restore it. They only tend to do this for people who come with several $10000 or a court order though, so if the most sensitive bit of information on that HDD is your facebook password, nobody will bother.

If you do have sensitive information on that drive, I’d follow @jpmc26’s advice and simply keep the drive for myself. This is 100% secure with close to zero chance to screw something up in the process.

Method 7

You can use the secure-delete tool , which provide 4 useful commands to wipe your hdd.

man srm

is designed to delete data on mediums in a secure manner which can
not be recovered by thiefs, law enforcement or other threats. The wipe
algorythm is based on the paper “Secure Deletion of Data from Magnetic
and Solid-State Memory” presented at the 6th Usenix Security Symposium
by Peter Gutmann, one of the leading civilian cryptographers.

Wiping your disk drive clean

Everybody who owns a computer will someday need to dispose of a disk drive. Before you do, it is a good idea to cleanse the drive, so no one can read your sensitive information. Deleting files and reformatting is not sufficient; determined effort can still reveal data from a drive even after it appears to be gone. To do a more thorough job, I suggest using wipe.

The secure-delete options:

srm is used for deleting files and directories.
smem wipes memory space.
sfill cleanses the free space on a drive.
sswap cleans swap spaces.

Note the all the tools used to wipe the hard drive isn’t granted , some forensic tools can recover a part of your hard drive data (mails , urls , photos ….).

Method 8

If you have a HDD you can do it the “hardware way” – just take an inductor with a gap big enough for the drive, plug it into AC and drag the drive through the gap. Keep in mind that it will also destroy some kind of hard drive drivers and you will need professional help in order to have the hard drive running once again.

You can read more about it on Wikipedia. There are even companies who can degauss a HDD for you. If you want to be sure – the only NSA-approved method of destroying a hard drive is shredding a degaussed drive.

However, the easiest way would be just overwriting whole drive with zeros.

Method 9

If your laptop used whole disk encryption from the start, a simple erase and you are good to go!

Method 10

The necessity of multi-pass overwrite was valid 35 years ago but has been obsolete for 25-30 years.

The Urban Legend of Multipass Hard Disk Overwrite (archived link)

Fortunately, several security researchers presented a paper [WRIG08] at the Fourth International Conference on Information Systems Security (ICISS 2008) that declares the “great wiping controversy” about how many passes of overwriting with various data values to be settled: their research demonstrates that a single overwrite using an arbitrary data value will render the original data irretrievable even if MFM and STM techniques are employed.

The researchers found that the probability of recovering a single bit from a previously used HDD was only slightly better than a coin toss, and that the probability of recovering more bits decreases exponentially so that it quickly becomes close to zero.

Therefore, a single pass overwrite with any arbitrary value (randomly chosen or not) is sufficient to render the original HDD data effectively irretrievable.
[WRIG08] Craig Wright; Dave Kleiman; R.S. Shyaam Sundhar (December 2008). “Overwriting Hard Drive Data: The Great Wiping Controversy” Lecture Notes in Computer Science (Springer Berlin / Heidelberg); ISBN 978-3-540-89861-0 (http://www.springerlink.com/content/408263ql11460147/). Some pages available for preview in Google Books.

Thus, this is all you need:

sudo dd if=/dev/zero of=/dev/sda bs=4M oflag=direct

Method 11

The best thing to do is to copy either some random data or just null data to the drive that the OS is installed on. If it is installed on sda, you can do something like dd if=/dev/zero of=/dev/sda bs=xxx count=1. Instead of xxx you want to find your disk’s size, or dd if=/dev/null of=/dev/sda. I personally like this one better.

Method 12

If you want to completely destroy the operating system and everything on it you can use:

sudo chmod -r 755 /

I have did this by accident once and it destroyed my operating system. My operating system was destroyed immediately and I could not boot it anymore. I had to boot a new operating system off of a disc. I do not know how this works. I have also heard of:

sudo chmod -r 000 /

Which works by removing all permissions to the hard drive, but I do not know why the other one works and maybe this one works that way to.
I could not get any of my files back.
To be safe you would want to boot a new operating system over top of the destroyed one, but even using a live USB or another computer I do not think the files were recoverable. When I ran the above command random numbers stared scrolling on my screen (no idea why) and then after I pressed the power button to force a shutdown my computer would not boot at all(bios and that was it).

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0