sudo apt-get install php-xml
service apache2 restart
cp -r phpBB3 /var/www/html
chown www-data:www-data -R /var/www/html/phpBB3
chmod 775 -R /var/www/html/phpBB3
mysql -uroot -p
create database phpbb;
check the requirements, if you have a message:
Directory is not writable
sudo usermod -aG www-data <your_user>
sudo chown -R www-data:www-data /var/www/html/
sudo chmod 660 images/avatars/upload/ config.php
sudo chmod 770 store/ cache/ files/
After those procedures will work file the requirements and you carry on the steps about the installation and configuration.
So, now you must rename or dell the folder install inside of /var/www/html/phpBB3/
in my case was renamed folder phpBB3 for phpbb and inside of folder: "/var/www/html/phpbb" was renamed the folder install for installl.
After that was possible to see everthing about the forum phpbb.
In some cases for attached files was necessary add this configuration about extension GD on my php server:
sudo add-apt-repository ppa:ondrej/php
sudo apt-get update
sudo apt-get install php7.0-gd