hadoop FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Incompatible build

datanode起不来，日志为：

STARTUP_MSG: Starting DataNode
STARTUP_MSG:   host = ip-172-19-1-3/172.19.1.3
STARTUP_MSG:   args = []
STARTUP_MSG:   version = 0.20.2-cdh3u0
STARTUP_MSG:   build =  -r 81256ad0f2e4ab2bd34b04f53d25a6c23686dd14; compiled by 'root' on Sat Mar 26 00:12:30 UTC 2011
************************************************************/
2011-08-11 09:45:42,240 INFO org.apache.hadoop.security.UserGroupInformation: JAAS Configuration already set up for Hadoop, not re-installing.
2011-08-11 09:45:42,370 FATAL org.apache.hadoop.hdfs.server.datanode.DataNode: Incompatible build versions: namenode BV = bdafb1dbffd0d5f2fbc6ee022e1c8df6500fd638; datanode BV = 81256ad0f2e4ab2bd34b04f53d25a6c23686dd14
2011-08-11 09:45:42,473 ERROR org.apache.hadoop.hdfs.server.datanode.DataNode: java.io.IOException: Incompatible build versions: namenode BV = bdafb1dbffd0d5f2fbc6ee022e1c8df6500fd638; datanode BV = 81256ad0f2e4ab2bd34b04f53d25a6c23686dd14
        at org.apache.hadoop.hdfs.server.datanode.DataNode.handshake(DataNode.java:555)
        at org.apache.hadoop.hdfs.server.datanode.DataNode.startDataNode(DataNode.java:350)

这是由于master和slave不一致造成的，这时可以把更新namenode和datanode来解决：

master上执行：hadoop namenode -upgrade

slave上执行：hadoop datanode -upgrade