How to disable directory listings on apache running on Ubuntu

open /etc/apache2/apache2.conf

And the section of the settings that deals with listing directory in Apahce2 default root directory is this:

<Directory /var/www/>  Options Indexes FollowSymLinks  AllowOverride None  Require all granted  </Directory>  

To disable directory listing, edit the setting to be this:

<Directory /var/www/>  Options FollowSymLinks  AllowOverride None  Require all granted  </Directory>  

Save the file and restart Apache2 to load the new configuration settings.