i son/pa ppid pid fpid 0 parent 2256 17040 17041 1 parent 2256 17040 17042 2 parent 2256 17040 17043 2 child 955 17043 0 1 child 955 17042 0 2 parent 955 17042 17044 0 child 955 17041 0 1 parent 955 17041 17045 2 parent 955 17041 17046 2 child 955 17044 0 2 child 955 17046 0 1 child 955 17045 0 2 parent 955 17045 17047 2 child 955 7047 0
上图是fork()连续三次的结果，做图如下：
