Beginner guide of systemd on CentOS7/RHEL7
Introduction of systemd 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 system. From CentOS 7, the systemd become the new system