This is a weird issue as sometimes when upgrading or even migrating, this could happen and the reason is simple but maybe not 100% obvious at first.
You will find that your GUIdoesn't load and most services fail to start, even logind
Here are some errors you may see:
Mar 13 22:22:23 rttbox systemd-logind[2892]: Failed to connect to system bus: No such file or directory
Mar 13 22:22:23 rttbox systemd-logind........
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:
Unit Commands:
list-units [PATTERN...] List loaded units
&nbs........