主namenode 为standly状态，备namenode为active，kill备namenode，主namenode能正常切换为active。但是主namenode为active，备namenode为standby，kill主namenode，备namenode却无法切换成active状态，必须把主namenode启动才能切换成active
java.net.ConnectException: Call From vir02/192.168.37.14 to vir01:8020 failed on connection exception: java.net.ConnectException: Connection refused
vir02无法连接vir01,由于vir02没有做免密码登录vir01，vir01只能免密码登录vir02
注：Namenode之间都要做免密登录