最近需要升级hadoop，从hadoop-2.2.0升级到hadoop-2.6.0，根据http://hadoop.apache.org/docs/r2.6.0/hadoop-project-dist/hadoop-hdfs/HdfsRollingUpgrade.html#dfsadmin_-rollingUpgrade 提示的来，第一步：./bin/hdfs dfsadmin -rollingUPgrade prepare 就出现了：PREPARE rolling upgrade ...
rollingUpgrade: Unknown method rollingUpgrade called on org.apache.hadoop.hdfs.protocol.ClientProtocol protocol.
试试看先升级2.4看看。执行bin/start-dfs.sh -upgrade
可以直接用源码新安装2.6版本，这样问题少一点。