hadoop问题

今天 在 ubuntu上 运 行 hadoop的 示例 出 错

java.net.ConnectException: Call to localhost/127.0.0.1:8021 failed on connection exception: java.net.ConnectException: Connection refused
    at org.apache.hadoop.ipc.Client.wrapException(Client.java:932)
    at org.apache.hadoop.ipc.Client.call(Client.java:908)
    at org.apache.hadoop.ipc.WritableRpcEngine$Invoker.invoke(WritableRpcEngine.java:198)
    at $Proxy0.getProtocolVersion(Unknown Source)
    at org.apache.hadoop.ipc.WritableRpcEngine.getProxy(WritableRpcEngine.java:228)
    at org.apache.hadoop.ipc.RPC.getProxy(RPC.java:224)
    at org.apache.hadoop.mapreduce.Cluster.createRPCProxy(Cluster.java:82)
    at org.apache.hadoop.mapreduce.Cluster.createClient(Cluster.java:94)
    at org.apache.hadoop.mapreduce.Cluster.<init>(Cluster.java:70)
    at org.apache.hadoop.mapreduce.Job.<init>(Job.java:129)
    at org.apache.hadoop.mapreduce.Job.<init>(Job.java:134)
    at org.apache.hadoop.examples.WordCount.main(WordCount.java:75)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.ProgramDriver$ProgramDescription.invoke(ProgramDriver.java:72)
    at org.apache.hadoop.util.ProgramDriver.driver(ProgramDriver.java:144)
    at org.apache.hadoop.examples.ExampleDriver.main(ExampleDriver.java:68)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:192)
Caused by: java.net.ConnectException: Connection refused
    at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
    at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:574)
    at org.apache.hadoop.net.SocketIOWithTimeout.connect(SocketIOWithTimeout.java:206)
    at org.apache.hadoop.net.NetUtils.connect(NetUtils.java:373)
    at org.apache.hadoop.ipc.Client$Connection.setupIOstreams(Client.java:417)
    at org.apache.hadoop.ipc.Client$Connection.access$1900(Client.java:207)
    at org.apache.hadoop.ipc.Client.getConnection(Client.java:1025)
    at org.apache.hadoop.ipc.Client.call(Client.java:885)
    ... 22 more

   原因 hadoop没 启动 ,调用 exec start-all.sh就可启动，在21版本中start-all.sh好像启动不成功