fork树

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：