在运行一段时间后，突然报出hadoop不识别指令的错误。因为曾正确使用过，观察所在目录已变化，考虑是环境变量JAVA_HOME的问题。

/etc/profile中JAVA_HOME变量已修改。

考虑到hadoop2.2.0官方文档提及其他变量，如下补充。

vim /etc/profile

在/etc/profile文件的末尾加上以下配置
04	  
05	export HADOOP_DEV_HOME=/home/wyp/Downloads/hadoop/hadoop-2.2.0
06	export PATH=$PATH:$HADOOP_DEV_HOME/bin
07	export PATH=$PATH:$HADOOP_DEV_HOME/sbin
08	export HADOOP_MAPARED_HOME=${HADOOP_DEV_HOME}
09	export HADOOP_COMMON_HOME=${HADOOP_DEV_HOME}
10	export HADOOP_HDFS_HOME=${HADOOP_DEV_HOME}
11	export YARN_HOME=${HADOOP_DEV_HOME}
12	export HADOOP_CONF_DIR=${HADOOP_DEV_HOME}/etc/hadoop

结束后输入hadoop,返回：

Usage: hadoop [--config confdir] COMMAND
   where COMMAND is one of:
 fs          run a generic filesystem user client
 version       print the version
 jar <jar>      run a jar file
 checknative [-a|-h] check native hadoop and compression libraries availability
 distcp <srcurl> <desturl> copy file or directories recursively
 archive -archiveName NAME -p <parent path> <src>* <dest> create a hadoop archive
 classpath      prints the class path needed to get the
           Hadoop jar and the required libraries
 daemonlog      get/set the log level for each daemon
or
 CLASSNAME      run the class named CLASSNAME


Most commands print help when invoked w/o parameters.