the files/directories should be readable by the user that your apache
process is running as, but not owned or writable by it.

So, does that mean (something like) the following?

chmod 600 /var/www/html/nagiosQL (where the index.php file is located)

also, have you added "index.php" to the appropriate DirectoryIndex
directive line in your httpd.conf? [when you install php via an rpm
that may get done by default, but you'll want to check.]

Actually, I do have that setup

httpd.conf -> DirectoryIndex index.html index.html.var index.php

And afterwards, I ran "/etc/init.d/httpd reload"