Your dataroot directory is in the wrong location and is exposed to the web. This means that all your private files are available to anyone in the world, and some of them could be used by a cracker to obtain unauthorised administrative access to your site!
You must move dataroot directory (/var/www/html/moodledata) to a new location that is not within your public web directory, and update the
$CFG->dataroot setting in your config.php accordingly.
i don't know it's mean and how to solve ploblem