Fix error ‘index.php was not found on this server’ after upgrading ownCloud to version 9

If you just upgraded ownCloud on Ubuntu 15.10 to version 9 (using apt-get dist upgrade), you probably get the error message shown above. Adding /index.php manually still redirects to the ownCloud login screen. As mentioned here open .htaccess in /var/www/owncloud an comment out the line RewriteRule .* index.php [PT,E=PATH_INFO:$1] and restart apache with service apache2 restart