How do I format my computer to be unrecoverable?

Question

I have a 500Gb HDD hard disk in my Laptop, and I want to sell it, so I am asking if I can format it such that no one can recover my old data, and if yes, How can I do that? Thanks in advance

Answer 1

You can securely delete all the files with a program like shred
It overwrites the files before deleting them, so that a recovery wont get success

You can also overwrite all the HDD and, then, format it

See shred program : http://manpages.ubuntu.com/manpages/trusty/man1/shred.1.html
Or overwrite with dd if=/dev/urandom of=/dev/sdX bs=4096 status=progress then format the drive