HDD temp won't show via web
in order to run some root privileged command in website, you need to put www-data in your /etc/sudoers to allow the www-data to run as root for the command, here is the line you need in /etc/sudoers:
www-data ALL=(root) NOPASSWD: /usr/sbin/smartctl
When executing under your web server, your script will probably have a different PATH configured, so it will run differently from how it runs in the Terminal.
Try putting the full path to smartctl in your script, e.g.
sudo /usr/local/bin/smartctl -A -d sat /dev/sda | awk '/^194/ {print $10}'