FastCGI sent in stderr: "Unable to open primary script" — Browser returns a 404 when accessing PHP pages.
Cause: php-fpm permission issue (using my php-fpm setup as an example)
vi /usr/local/php/etc/php-fpm.conf
service php-fpm restart # Restart the service (using my startup method as an example)
Change the user to match the user specified in the nginx.conf file.