systemd 架构图

systemd提供更优秀的框架以表示系统服务间的依赖关系
实现系统初始化时服务的并行启动，同时达到降低Shell的系统开销的效果
systemd的目标是：尽可能启动更少进程；尽可能将更多进程并行启动。
systemd尽可能减少对shell脚本的依赖。

systemdis a suite of basic building blocks for a Linux system. It provides a system and service manager that runs as PID 1 and starts the rest of the system.provides aggressive parallelization capabilities,uses socket and D-Bus activation for starting services,offers on-demand starting of daemons,keeps track of processes using Linux control groups,maintains mount and automount points,and implements an elaborate transactional dependency-based service control logic.supports SysV and LSB init scripts and works as a replacement for sysvinit. Other parts include a logging daemon,utilities to control basic system configuration like the hostname,date,locale,maintain a list of logged-in users and running containers and virtual machines,system accounts,runtime directories and settings,and daemons to manage simple network configuration,network time synchronization,log forwarding,and name resolution. SeeLennart's blog storyfor a longer introduction,and thethreestatusupdatessince then. Also see theWikipedia article. If you are wondering whether systemd is for you,please have a lookat this comparison of init systems by one of the creators of systemd.