第六步：安装验证
可以通过ZooKeeper的脚本来查看启动状态，包括集群中各个结点的角色（或是Leader，或是Follower），如下所示，是在ZooKeeper集群中的每个结点上查询的结果：
Hadoop@slave-01:~/installation/zookeeper-3.3.4$ bin/zkServer.sh status JMX enabled by default Using config: /home/hadoop/installation/zookeeper-3.3.4/bin/../conf/zoo.cfg Mode: follower hadoop@slave-02:~/installation/zookeeper-3.3.4$ bin/zkServer.sh status JMX enabled by default Using config: /home/hadoop/installation/zookeeper-3.3.4/bin/../conf/zoo.cfg Mode: leader hadoop@slave-03:~/installation/zookeeper-3.3.4$ bin/zkServer.sh status JMX enabled by default Using config: /home/hadoop/installation/zookeeper-3.3.4/bin/../conf/zoo.cfg Mode: follower
通过上面状态查询结果可见，slave-02是集群的Leader，其余的两个结点是Follower。另外，可以通过客户端脚本，连接到ZooKeeper集群上。对于客户端来说，ZooKeeper是一个整体（ensemble），连接到ZooKeeper集群实际上感觉在独享整个集群的服务，所以，你可以在任何一个结点上建立到服务集群的连接，例如：
hadoop@slave-03:~/installation/zookeeper-3.3.4$ bin/zkCli.sh -server slave-01:2181 Connecting to slave-01:2181 2012-01-08 07:14:21,068 - INFO [main:Environment@97] - Client environment:zookeeper.version=3.3.3-1203054, built on 11/17/2011 05:47 GMT 2012-01-08 07:14:21,080 - INFO [main:Environment@97] - Client environment:host.name=slave-03 2012-01-08 07:14:21,085 - INFO [main:Environment@97] - Client environment:Java.version=1.6.0_30 2012-01-08 07:14:21,089 - INFO [main:Environment@97] - Client environment:java.vendor=Sun Microsystems Inc. 2012-01-08 07:14:21,095 - INFO [main:Environment@97] - Client environment:java.home=/home/hadoop/installation/jdk1.6.0_30/jre 2012-01-08 07:14:21,104 - INFO [main:Environment@97] - Client environment:java.class.path=/home/hadoop/installation/zookeeper-3.3.4/bin/../build/classes:/home/hadoop/installation/zookeeper-3.3.4/bin/../build/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../zookeeper-3.3.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/log4j-1.2.15.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/jline-0.9.94.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-lang-2.4.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-collections-3.2.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/commons-cli-1.1.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-tasks-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../lib/apache-rat-core-0.6.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../src/java/lib/*.jar:/home/hadoop/installation/zookeeper-3.3.4/bin/../conf:/home/hadoop/installation/jdk1.6.0_30/lib/*.jar:/home/hadoop/installation/jdk1.6.0_30/jre/lib/*.jar 2012-01-08 07:14:21,111 - INFO [main:Environment@97] - Client environment:java.library.path=/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386/client:/home/hadoop/installation/jdk1.6.0_30/jre/lib/i386:/home/hadoop/installation/jdk1.6.0_30/jre/../lib/i386:/usr/java/packages/lib/i386:/lib:/usr/lib 2012-01-08 07:14:21,116 - INFO [main:Environment@97] - Client environment:java.io.tmpdir=/tmp 2012-01-08 07:14:21,124 - INFO [main:Environment@97] - Client environment:java.compiler=<NA> 2012-01-08 07:14:21,169 - INFO [main:Environment@97] - Client environment:os.name=Linux 2012-01-08 07:14:21,175 - INFO [main:Environment@97] - Client environment:os.arch=i386 2012-01-08 07:14:21,177 - INFO [main:Environment@97] - Client environment:os.version=3.0.0-14-generic 2012-01-08 07:14:21,185 - INFO [main:Environment@97] - Client environment:user.name=hadoop 2012-01-08 07:14:21,188 - INFO [main:Environment@97] - Client environment:user.home=/home/hadoop 2012-01-08 07:14:21,190 - INFO [main:Environment@97] - Client environment:user.dir=/home/hadoop/installation/zookeeper-3.3.4 2012-01-08 07:14:21,197 - INFO [main:ZooKeeper@379] - Initiating client connection, connectString=slave-01:2181 sessionTimeout=30000 watcher=org.apache.zookeeper.ZooKeeperMain$MyWatcher@bf32c 2012-01-08 07:14:21,305 - INFO [main-SendThread():ClientCnxn$SendThread@1061] - Opening socket connection to server slave-01/192.168.0.179:2181 Welcome to ZooKeeper! 2012-01-08 07:14:21,376 - INFO [main-SendThread(slave-01:2181):ClientCnxn$SendThread@950] - Socket connection established to slave-01/192.168.0.179:2181, initiating session JLine support is enabled [zk: slave-01:2181(CONNECTING) 0] 2012-01-08 07:14:21,872 - INFO [main-SendThread(slave-01:2181):ClientCnxn$SendThread@739] - Session establishment complete on server slave-01/192.168.0.179:2181, sessionid = 0x134bdcd6b730000, negotiated timeout = 30000 WATCHER:: WatchedEvent state:SyncConnected type:None path:null [zk: slave-01:2181(CONNECTED) 0] ls / [zookeeper]
当前根路径为/zookeeper。总结说明
主机名与IP地址映射配置问题
启动ZooKeeper集群时，如果ZooKeeper集群中slave-01结点的日志出现如下错误：
java.net.SocketTimeoutException at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:109) at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371) at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404) at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688) at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622) 2012-01-08 06:37:46,026 - INFO [QuorumPeer:/0:0:0:0:0:0:0:0:2181:FastLeaderElection@697] - Notification time out: 6400 2012-01-08 06:37:57,431 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 2 at election address slave-02/202.106.199.35:3888 java.net.SocketTimeoutException at sun.nio.ch.SocketAdaptor.connect(SocketAdaptor.java:109) at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectOne(QuorumCnxManager.java:371) at org.apache.zookeeper.server.quorum.QuorumCnxManager.connectAll(QuorumCnxManager.java:404) at org.apache.zookeeper.server.quorum.FastLeaderElection.lookForLeader(FastLeaderElection.java:688) at org.apache.zookeeper.server.quorum.QuorumPeer.run(QuorumPeer.java:622) 2012-01-08 06:38:02,442 - WARN [QuorumPeer:/0:0:0:0:0:0:0:0:2181:QuorumCnxManager@384] - Cannot open channel to 3 at election address slave-03/202.106.199.35:3888
很显然，slave-01在启动时连接集群中其他结点（slave-02、slave-03）时，主机名映射的IP与我们实际配置的不一致，所以集群中各个结点之间无法建立链路，整个ZooKeeper集群启动是失败的。
上面错误日志中slave-02/202.106.199.35:3888实际应该是slave-02/202.192.168.0.178:3888就对了，但是在进行域名解析的时候映射有问题，修改每个结点的/etc/hosts文件，将ZooKeeper集群中所有结点主机名到IP地址的映射配置上。