进程控制实例
............\dead.c
............\exec
............\execlp.c
............\....\exec.c
............\....\newcode.c
............\....\test.txt
............\exit.c
............\fork1.c
............\fork2.c
............\fork_descriptor.c
............\getpgid.c
............\orphan.c
............\other
............\.....\fork.c
............\.....\waitpid.c
............\vfork.c
............\vfork_return.c
............\wait.c
............\zombie.c