命令格式：
systemctl [command] [unit.target]
[command]
[unit.target]
可以使用man runlevel来查询
参考文献：
/Martin0316/article/details/106215554?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.channel_param
