Change the site configuration file to block listing out files in the directory - apache2 + Ubuntu

When I access a directory hosted by Apache that does not have a index.php file or similar, Apache lists the content of the directory for me. How can I block this? I'm using Apache2 on Ubuntu.

In the appropriate <Directory> stanza. For instance it may look like this:

<Directory /www/somefolder>
    Options Indexes FollowSymLinks
    AllowOverride None
</Directory>

Change this into

<Directory /www/somefolder>
    Options -Indexes FollowSymLinks
    AllowOverride None
</Directory>

If there is no Options... line, you can add one with the content Options -Indexes for any <Directory...> stanza. The options are separated by a space ().

Note the - in front of Indexes. This is also covered briefly in the Apache documentation.

The index are generated by mod_autoindex.