This is all controlled by /etc/issue
You can basically enter anything in there that you like, but there are preset variables that are mentioned at the end of the page that discuss this.
Some examples of /etc/issue:
Kernel r on an m
Ubuntu 16.04.6 LTS n l
You can also insert any of t........
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