我正在为hdfs尝试hadoop2高可用性。我在userhafence下的namenodes之间建立了无密码ssh连接。我证实了-而且它是有效的。但是，当使用此sshfence安装程序时，我会收到以下消息（权限被拒绝）。

2014-01-20 12:54:47,101 INFO  ha.NodeFencer (NodeFencer.java:fence(91)) - ====== Beginning Service Fencing Process... ======
2014-01-20 12:54:47,101 INFO  ha.NodeFencer (NodeFencer.java:fence(94)) - Trying method 1/1: org.apache.hadoop.ha.SshFenceByTcpPort(hafence:22)
2014-01-20 12:54:47,101 WARN  ha.SshFenceByTcpPort (SshFenceByTcpPort.java:tryFence(93)) - Unable to create SSH session
com.jcraft.jsch.JSchException: java.io.FileNotFoundException: /home/hafence/.ssh/id_rsa (Permission denied)
    at com.jcraft.jsch.IdentityFile.newInstance(IdentityFile.java:98)
    at com.jcraft.jsch.JSch.addIdentity(JSch.java:206)
    at com.jcraft.jsch.JSch.addIdentity(JSch.java:192)
    at org.apache.hadoop.ha.SshFenceByTcpPort.createSession(SshFenceByTcpPort.java:122)
    at org.apache.hadoop.ha.SshFenceByTcpPort.tryFence(SshFenceByTcpPort.java:91)
    at org.apache.hadoop.ha.NodeFencer.fence(NodeFencer.java:97)
    at org.apache.hadoop.ha.ZKFailoverController.doFence(ZKFailoverController.java:521)
    at org.apache.hadoop.ha.ZKFailoverController.fenceOldActive(ZKFailoverController.java:494)
    at org.apache.hadoop.ha.ZKFailoverController.access$1100(ZKFailoverController.java:59)
    at org.apache.hadoop.ha.ZKFailoverController$ElectorCallbacks.fenceOldActive(ZKFailoverController.java:837)
    at org.apache.hadoop.ha.ActiveStandbyElector.fenceOldActive(ActiveStandbyElector.java:900)
    at org.apache.hadoop.ha.ActiveStandbyElector.becomeActive(ActiveStandbyElector.java:799)
    at org.apache.hadoop.ha.ActiveStandbyElector.processResult(ActiveStandbyElector.java:415)
    at org.apache.zookeeper.ClientCnxn$EventThread.processEvent(ClientCnxn.java:596)
    at org.apache.zookeeper.ClientCnxn$EventThread.run(ClientCnxn.java:495)
Caused by: java.io.FileNotFoundException: /home/hafence/.ssh/id_rsa (Permission denied)
    at java.io.FileInputStream.open(Native Method)
    at java.io.FileInputStream.<init>(FileInputStream.java:138)
    at java.io.FileInputStream.<init>(FileInputStream.java:97)
    at com.jcraft.jsch.IdentityFile.newInstance(IdentityFile.java:83)
    ... 14 more
2014-01-20 12:54:47,102 WARN  ha.NodeFencer (NodeFencer.java:fence(108)) - Fencing method org.apache.hadoop.ha.SshFenceByTcpPort(hafence:22) was unsuccessful.
2014-01-20 12:54:47,102 ERROR ha.NodeFencer (NodeFencer.java:fence(111)) - Unable to fence service by any configured method.
2014-01-20 12:54:47,102 WARN  ha.ActiveStandbyElector (ActiveStandbyElector.java:becomeActive(807)) - Exception handling the winning of election

我在hdfs-site.xml中的配置如下：

<property>
    <name>dfs.ha.fencing.methods</name>
    <value>sshfence(hafence:22)</value>
  </property>
  <property>
    <name>dfs.ha.fencing.ssh.private-key-files</name>
    <value>/home/hafence/.ssh/id_rsa</value>
  </property>
  <property>
    <name>dfs.ha.fencing.ssh.connect-timeout</name>
    <value>30000</value>
  </property>

  <property>
    <name>dfs.ha.automatic-failover.enabled</name>
    <value>true</value>
  </property>

为了使sshfence工作，有哪些权限要求、用户等？