搭建好hadoop集群之后，运行start-all.sh脚本，发现有如下报错
starting namenode, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-namenode-we-home-server.out homeserver: starting datanode, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-datanode-homeserver.out we-home-server: starting secondarynamenode, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-secondarynamenode-we-home-server.out we-home-server: Exception in thread "main" java.net.BindException: Address already in use we-home-server: at sun.nio.ch.Net.bind(Native Method) we-home-server: at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:124) we-home-server: at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:59) we-home-server: at org.mortbay.jetty.nio.SelectChannelConnector.open(SelectChannelConnector.java:216) we-home-server: at org.apache.hadoop.http.HttpServer.start(HttpServer.java:581) we-home-server: at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode$1.run(SecondaryNameNode.java:216) we-home-server: at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode$1.run(SecondaryNameNode.java:190) we-home-server: at java.security.AccessController.doPrivileged(Native Method) we-home-server: at javax.security.auth.Subject.doAs(Subject.java:396) starting jobtracker, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-jobtracker-we-home-server.out
log中说明错误 Address already in use，这是因为有上次的运行datanode的进程没有终止，解决方法，
netstat -antup
运行这个命令后，找出占用50030端口的那个进程的PID，然后将其终止
kill -9 <PID>
然后，再重新启动hadoop集群，没有报错。
hadoop@we-home-server:/usr/local/hadoop/bin$ ./start-all.sh starting namenode, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-namenode-we-home-server.out homeserver: starting datanode, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-datanode-homeserver.out we-home-server: starting secondarynamenode, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-secondarynamenode-we-home-server.out starting jobtracker, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-jobtracker-we-home-server.out homeserver: starting tasktracker, logging to /usr/local/hadoop/libexec/../logs/hadoop-hadoop-tasktracker-homeserver.out hadoop@we-home-server:/usr/local/hadoop/bin$