配置完执行hadoop报-bash: hadoop: command not found！！！也配置了hadoop_home并且保存生效了！！！
export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64/
export JRE_HOME=$JAVA_HOME/jre
export HADOOP_HOME=/opt/hadoop-1.2.1
export CLASSPATH=$JAVA_HOME/lib:$JRE_HOME/lib:$CLASSPATH
export PATH=$JAVA_HOME/bin:$JRE_HOME/bin:$HADOOP_HOME/bin:$PATH
