nginx - nginx: [emerg] bind() to [::]:80 failed (98: Address already in use)

My case is different, I had to kill the running Nginx process to restart it.

Instead of

sudo systemctl restart nginx

I had to use:

sudo pkill -f nginx & wait $!
sudo systemctl start nginx

I fixed this by running:

sudo apachectl stop

It turns out apache was running in the background and prevented nginx from starting on the desired port.

On Ubuntu, run:

sudo /etc/init.d/apache2 stop