1.互信的机器都执行(合并id_rsa.pub文件)
ssh-keygen -t rsa
cat ~/.ssh/id_rsa.pub >> /home/hdfs/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys
2.拷贝第一台的authorized_keys 到第二台机器
3.追加第二台机器的id_rsa.pub到authorized_keys
cat ~/.ssh/id_rsa.pub >> authorized_keys
4.拷贝回第一台,替换authorized_keys
5.ssh nn1 ssh nn2