hadoop执行hadoop namenode -format错误问题

运行时遇到如下问题：
Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/hadoop/hdfs/server/namenode/NameNode
Caused by: java.lang.ClassNotFoundException: org.apache.hadoop.hdfs.server.namenode.NameNode
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: org.apache.hadoop.hdfs.server.namenode.NameNode.  Program will exit.

可修改 conf/hadoop-env.sh，增加
export HADOOP_COMMON_HOME=/usr/hadoop/ （hadoop的安装目录)
并且把JAVA_HOME配置好