I just set up the apache2/mysql server to play around with. But I found the something different than what I saw before. The root directory is pointed to /var/www/html/. I checked the /etc/apache2/apache2.conf file ,and says
<Directory /var/www/>
Options Indexes FollowSymLinks
AllowOverride None
Require all granted
</Directory>
This says the root directory points to /var/www/. Is this a bug ? And I also want to know why they made /var/www/html instead of /var/www/.