本文记录MapReduce过程中遇到的问题及解决，持续更新。
1、运行程序，提示"JobTracker is in safe mode"
[huser@master bin]$ ../bin/hadoop jar AvgTemperature.jar AvgTemperature ./in/sample.txt ./out1 Warning: $HADOOP_HOME is deprecated. 14/04/18 20:12:39 ERROR security.UserGroupInformation: PriviledgedActionException as:huser cause:org.apache.hadoop.ipc.RemoteException: org.apache.hadoop.mapred.SafeModeException: JobTracker is in safe mode at org.apache.hadoop.mapred.JobTracker.checkSafeMode(JobTracker.java:5188) at org.apache.hadoop.mapred.JobTracker.getStagingAreaDir(JobTracker.java:3677) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:587) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1432) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:1428) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:415) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1190) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:1426)
JobTracker处于安全模式，需要退出安全模式，再运行。
[huser@master bin]$ ../bin/hadoop dfsadmin -safemode leave Warning: $HADOOP_HOME is deprecated. Safe mode is OFF
2、上传文件到hdfs，发现报错。
[hadoop@hadoop1 hadoop220]$ bin/hadoop fs -put NOTICE.txt /user/hadoop/data 14/07/10 22:32:51 WARN hdfs.DFSClient: DataStreamer Exception org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /user/hadoop/data/NOTICE.txt._COPYING_ could only be replicated to 0 nodes instead of minReplication (=1). There are 0 datanode(s) running and no node(s) are excluded in this operation. at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget(BlockManager.java:1384) at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2477) at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:555) at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:387) at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java:59582) at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:585) at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:928) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2048) at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2044) at java.security.AccessController.doPrivileged(Native Method) at javax.security.auth.Subject.doAs(Subject.java:415) at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1491) at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2042) at org.apache.hadoop.ipc.Client.call(Client.java:1347) at org.apache.hadoop.ipc.Client.call(Client.java:1300) at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:206) at com.sun.proxy.$Proxy9.addBlock(Unknown Source) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:186) at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:102) at com.sun.proxy.$Proxy9.addBlock(Unknown Source) at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:330) at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.locateFollowingBlock(DFSOutputStream.java:1226) at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.nextBlockOutputStream(DFSOutputStream.java:1078) at org.apache.hadoop.hdfs.DFSOutputStream$DataStreamer.run(DFSOutputStream.java:514)
意思没有连接到namenode的datanode，但是在slave节点上jps，datanode进程是存在的。
用hadoop dfsadmin -report命令查看，发现确实是0个datanode。
[hadoop@hadoop1 hadoop220]$ bin/hadoop dfsadmin -report DEPRECATED: Use of this script to execute hdfs command is deprecated. Instead use the hdfs command for it. Configured Capacity: 0 (0 B) Present Capacity: 0 (0 B) DFS Remaining: 0 (0 B) DFS Used: 0 (0 B) DFS Used%: NaN% Under replicated blocks: 0 Blocks with corrupt replicas: 0 Missing blocks: 0 ------------------------------------------------- Datanodes available: 0 (0 total, 0 dead)
怀疑是防火墙问题，所有都检查关闭。