Ok.
It seems i decided to enter no root password for mysql while running the installation, after I tried to configure a less secure root password.

After setting a very very strong password on mysql root account (phpmyadmin).
You have to manually edit:

sudo nano /var/www/fog/lib/fog/Config.class.php

In my case, for Ubuntu 18.04.1 LTS
sudo nano /var/www/html/fog/lib/fog/Config.class.php

private static function _dbSettings()
enter credentials.