In recent years, the INIT process of Linux system has undergone two major evolution, the traditional sysinit has gradually faded out of the historical stage, the new upstart and Systemd have their own characteristics, A growing number of Linux distributions have adopted systemd. RHEL 7.0 also started using SYSTEMD.
systemd is the latest initialization system (INIT) in Linux, and its main design goal is to overcome the inherent shortcomings of sysinit and improve the system startup speed. Systemd and Ubuntu upstart are rivals and are expected to replace upstart, and there are reports that Ubuntu will also use SYSTEMD as its standard system initialization system.
SYSTEMD provides a more aggressive parallel start-up capability than upstart, using technology such as Socket/d-bus activation to start the service. One obvious result is that it has a faster start-up speed. To reduce the system start-up time, Systemd's goal is to:
SYSTEMD Introduction to Linux service Management