Introduction - If you have any usage issues, please Google them yourself
1. No. 2 process to create two processes
2. 2, the implementation of the process of system commands, ls, ps, cp and so on
3. 3, the process of creating two processes 4,5
4. 4, the process of creating two threads Thread1, Thread2
5. Thread1: loop speed out I am child1. 5 times
6. Thread2: loop output I am child2. 5 times
7. Process 5 s a user-written executable