systemd is like the service manager for your Centos and other modern Linux distributions (including Debian/Mint/Ubuntu) allows you to enable services, stop them, restart them, check their status and even reboot your system.
The key commands or arguments you will use with systemctl are the following:
list-units [PATTERN...] List loaded units
Almost always the reason will be that the php.so file is missing but also that php.conf is misconfigured.
In the problem machine it is actually PHP7 installed so if you reference PHP5 of course things wil be broken!
Take for example here:
# PHP is an HTML-embedded scripting language which attempts to make it
# easy for developers to write dynamica........
Stopping httpd: [ OK ]
Starting httpd: httpd: Syntax error on line 221 of /etc/httpd/conf/httpd.conf: Syntax error on line 6 of /etc/httpd/conf.d/php.conf: Cannot load /etc/httpd/modules/libphp5.so into server: /etc/h........