Introduction - If you have any usage issues, please Google them yourself
Implement Linux process management.
A. Create a child process through fork. Then the father-son process repeatedly prints "parent" and "child" and prints their pid, allowing the process to sleep for a while to see the effects of the father-son process cross execution.
B. Create child process A, b through fork. A process statistics the number of user home directory file and print the results, B process list with all the files in the directory, head of the household when wait for both the child process has been completed, the parent process after print out "child are completed!" Exit after information.