[Solved] Unable to connect to a as user root com.jcraft.jsch.JSchException: Auth failUnable to connect

The specific errors encountered in building Hadoop HA are as follows

com.jcraft.jsch.JSchException: Auth fail
	at com.jcraft.jsch.Session.connect(Session.java:452)
	at org.apache.hadoop.ha.SshFenceByTcpPort.tryFence(SshFenceByTcpPort.java:100)
	at org.apache.hadoop.ha.NodeFencer.fence(NodeFencer.java:97)
	at org.apache.hadoop.ha.ZKFailoverController.doFence(ZKFailoverController.java:532)
	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:902)
	at org.apache.hadoop.ha.ActiveStandbyElector.becomeActive(ActiveStandbyElector.java:801)
	at org.apache.hadoop.ha.ActiveStandbyElector.processResult(ActiveStandbyElector.java:416)
	at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:599)
	at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:498)
2021-12-27 11:07:20,846 WARN org.apache.hadoop.ha.NodeFencer: Fencing method org.apache.hadoop.ha.SshFenceByTcpPort(null) was unsuccessful.
2021-12-27 11:07:20,846 ERROR org.apache.hadoop.ha.NodeFencer: Unable to fence service by any configured method.
2021-12-27 11:07:20,846 WARN org.apache.hadoop.ha.ActiveStandbyElector: Exception handling the winning of election
java.lang.RuntimeException: Unable to fence NameNode at a/192.168.0.149:8020
	at org.apache.hadoop.ha.ZKFailoverController.doFence(ZKFailoverController.java:533)
	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:902)
	at org.apache.hadoop.ha.ActiveStandbyElector.becomeActive(ActiveStandbyElector.java:801)
	at org.apache.hadoop.ha.ActiveStandbyElector.processResult(ActiveStandbyElector.java:416)
	at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:599)
	at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:498)
2021-12-27 11:07:20,846 INFO org.apache.hadoop.ha.ActiveStandbyElector: Trying to re-establish ZK session
2021-12-27 11:07:20,851 INFO org.apache.zookeeper.ZooKeeper: Session: 0x37df9b417310059 closed
2021-12-27 11:07:21,852 INFO org.apache.zookeeper.ZooKeeper: Initiating client connection, connectString=a:2181,b:2181,c:2181 sessionTimeout=5000 watcher[email protected]44a90199
2021-12-27 11:07:21,853 INFO org.apache.zookeeper.ClientCnxn: Opening socket connection to server b/192.168.0.150:2181. Will not attempt to authenticate using SASL (unknown error)
2021-12-27 11:07:21,854 INFO org.apache.zookeeper.ClientCnxn: Socket connection established to b/192.168.0.150:2181, initiating session
2021-12-27 11:07:21,859 INFO org.apache.zookeeper.ClientCnxn: Session establishment complete on server b/192.168.0.150:2181, sessionid = 0x27df9b3aaf60068, negotiated timeout = 5000
2021-12-27 11:07:21,860 INFO org.apache.zookeeper.ClientCnxn: EventThread shut down
2021-12-27 11:07:21,861 INFO org.apache.hadoop.ha.ActiveStandbyElector: Session connected.
2021-12-27 11:07:21,862 INFO org.apache.hadoop.ha.ActiveStandbyElector: Checking for any old active which needs to be fenced...
2021-12-27 11:07:21,862 INFO org.apache.hadoop.ha.ActiveStandbyElector: Old node exists: 0a096d79636c757374657212026e311a016120d43e28d33e
2021-12-27 11:07:21,864 INFO org.apache.hadoop.ha.ZKFailoverController: Should fence: NameNode at a/192.168.0.149:8020
2021-12-27 11:07:22,866 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: a/192.168.0.149:8020. Already tried 0 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=1, sleepTime=1000 MILLISECONDS)
2021-12-27 11:07:22,867 WARN org.apache.hadoop.ha.FailoverController: Unable to gracefully make NameNode at a/192.168.0.149:8020 standby (unable to connect)
java.net.ConnectException: Call From b/192.168.0.150 to a:8020 failed on connection exception: java.net.ConnectException: Connection refused; For more details see:  http://wiki.apache.org/hadoop/ConnectionRefused
	at sun.reflect.GeneratedConstructorAccessor26.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:1480)
	at org.apache.hadoop.ipc.Client.call(Client.java:1407)
	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:902)
	at org.apache.hadoop.ha.ActiveStandbyElector.becomeActive(ActiveStandbyElector.java:801)
	at org.apache.hadoop.ha.ActiveStandbyElector.processResult(ActiveStandbyElector.java:416)
	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$Connection.setupConnection(Client.java:609)
	at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:707)
	at org.apache.hadoop.ipc.Client$Connection.access$2800(Client.java:370)
	at org.apache.hadoop.ipc.Client.getConnection(Client.java:1529)
	at org.apache.hadoop.ipc.Client.call(Client.java:1446)
	... 14 more

Here are two possible reasons for this error. You are also welcome to point out the shortcomings and discuss with us.

The first is that SSH secret login is not configured. You can try to report an error and log in with other machines to see if you can successfully log in without secret.

The second is because the parameter of dfs.ha.fencing.methods is sshence, and needs to use fuser command; maybe you do not install  fuser (required for each namenode node)
installation command: Yum - y install psmisc

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