System has not been booted with systemd as init system (PID 1).

If you get a

System has not been booted with systemd as init system (PID 1). Can't operate.
Failed to connect to bus: Host is down

this typically occurs when you're trying to use the systemctl command in an environment that does not support systemd as the init system.

Solution: Use Sysvinit

# Use the Below
sudo service start <service name> 

## Example below
sudo service start nginx

# Instead of 
sudo systemctl start <service name>