printf：＃include<stdio.h>
_exit(0):#include<unistd.h>
file(fd):#include<fcntl.h>
clone():#include<sched.h>
malloc():#include<malloc.h>
最重要的：#define _GNU_SOURCE
参考：
（2）＃define _GNU_SOURCE解释：
http://stackoverflow.com/questions/5582211/what-does-define-gnu-source-imply
原文：http://www.cnblogs.com/Z-D-/p/6786568.html