今天在学习HA自动化配置的时候，按照网上的教程去配置并启动HA即两台namenode后，看到一台为active模式，一台为standby模式，并且文件也可以正常写入。在做测试时，用 kill -9 端口号 杀死active的namenode后，standby的namenode并没有自动启动。
检查配置文件确保无误后，重启集群，发现依然无果。 查看logs->hadoop-root-zkfc-master.log,发现有如下报错信息：
2019-02-05 02:01:02,271 WARN org.apache.hadoop.ha.FailoverController: Unable to gracefully make NameNode at slave1/192.168.43.171:8020 standby (unable to connect)
java.net.ConnectException: Call From master/192.168.43.241 to slave1:8020 failed on connection exception: java.net.ConnectException: Connection refused; For more details see: http://wiki.apache.org/hadoop/ConnectionRefused
at sun.reflect.GeneratedConstructorAccessor28.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
at org.apache.hadoop.net.NetUtils.wrapWithMessage(NetUtils.java:792)
at org.apache.hadoop.net.NetUtils.wrapException(NetUtils.java:732)
at org.apache.hadoop.ipc.Client.call(Client.java:1479)
at org.apache.hadoop.ipc.Client.call(Client.java:1412)
at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:229)
at com.sun.proxy.$Proxy9.transitionToStandby(Unknown Source)
at org.apache.hadoop.ha.protocolPB.HAServiceProtocolClientSideTranslatorPB.transitionToStandby(HAServiceProtocolClientSideTranslatorPB.java:112)
at org.apache.hadoop.ha.FailoverController.tryGracefulFence(FailoverController.java:172)
at org.apache.hadoop.ha.ZKFailoverController.doFence(ZKFailoverController.java:514)
at org.apache.hadoop.ha.ZKFailoverController.fenceOldActive(ZKFailoverController.java:505)
at org.apache.hadoop.ha.ZKFailoverController.access$1100(ZKFailoverController.java:61)
at org.apache.hadoop.ha.ZKFailoverController$ElectorCallbacks.fenceOldActive(ZKFailoverController.java:892)
at org.apache.hadoop.ha.ActiveStandbyElector.fenceOldActive(ActiveStandbyElector.java:910)
at org.apache.hadoop.ha.ActiveStandbyElector.becomeActive(ActiveStandbyElector.java:809)
at org.apache.hadoop.ha.ActiveStandbyElector.processResult(ActiveStandbyElector.java:418)
at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:599)
at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:498)
Caused by: java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:531)
at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:495)
at org.apache.hadoop.ipc.Client$Connection.setupConnection(Client.java:614)
at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:712)
at org.apache.hadoop.ipc.Client$Connection.access$2900(Client.java:375)
at org.apache.hadoop.ipc.Client.getConnection(Client.java:1528)
at org.apache.hadoop.ipc.Client.call(Client.java:1451)
... 14 more
原来是未找到fuster程序，导致无法进行fence，所以可以通过如下命令来安装，Psmisc软件包中包含了fuster程序：
yum install psmisc
安装完毕后重启集群，问题解决。