Erase root password before reselling computer

I want to erase the root password I had set on my laptop, so that I can sell it. I currently have Ubuntu 16.04.

I've tried following some instruction videos on YouTube but they didn't work.

How can I erase the root password on my system?

Solution 1:

If you are selling the laptop it is a much better idea to wipe the hard disk completely, so that nobody can see your private information.

1. Boot from an Ubuntu live CD or USB.
2. Launch Disk and delete all partitions on the laptop's hard drive.
3. To go Format and where it says erase, select "Overwrite existing data with zeroes (slow).
4. Wait up to a few hours.

There are even more secure ways to erase the hard drive but overwriting with zeroes is the minimum that you should do.

Solution 2:

To lock / erase the root pw

sudo passwd -l root