https://colobu.com/2015/10/09/Linux-Signals/
https://blog.csdn.net/leonpengweicn/article/details/52131313?utm_medium=distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.control&depth_1-utm_source=distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.control