在執行一段時間後，突然報出hadoop不識別指令的錯誤。因為曾正確使用過，觀察所在目錄已變化，考慮是環境變數JAVA_HOME的問題。

/etc/profile中JAVA_HOME變數已修改。

考慮到hadoop2.2.0官方文件提及其他變數，如下補充。

vim /etc/profile

在/etc/profile檔案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
 

結束後輸入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.