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)?
Erasing a Linux laptop
linux;security;data destruction
This nixCraft post explain how to erase hard diskThe 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 cdFirst, 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/sdaWhere,-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/hdaNote: Comment from @GillesReplace 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/sda2. How to use the wipe commandYou can use wipe command to delete any file including disks:# wipe -D /path/to/file.doc3. How to use the scrub commandYou 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 fileNameHereTo erase /dev/sda, enter:# scrub -p dod /dev/sda4. Use dd command to securely wipe diskYou 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=4096Wipe a /dev/sda disk, enter:# dd if=/dev/urandom of=/dev/sda bs=40965. 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/sda399717171200Next, 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 -bartpes399717171200 | dd bs=64K of=/dev/sda6. How to use badblocks command to securely wipe diskThe syntax is:# badblocks -c BLOCK_SIZE_HERE -wsvf /dev/DISK/TO/WIPE# badblocks -wsvf /dev/DISK/TO/WIPE# badblocks -wsvf /dev/sda