Before CentOS 7 and RHEL 7, System V was used to be the system controller.
The system controller can manage all processes, services, and start task.
System V has a performance problem as it is using script to manage the tasks.
So it can only start the task serially, which will slow down the startup of the
From CentOS 7, the systemd become the new system controller. The biggest
change is it can start task parallel and will improve the startup speed. And as
the its PID is 1, the systemd is controlling every process in the system!
This article will only shows the information of “service”, “start up task”, and “log manage” by systemd.
systemctl list-unit-files --type=service