localhost: Error: JAVA_HOME is not set and could not be found.

今天开启 NameNode 和 DataNode 守护进程时出错

localhost: Error: JAVA_HOME is not set and could not be found.

但是JAVA环境变量已经配好了，终端输入java -version也会显示版本信息

解决方案如下
修改hadoop-env.sh (我的hadoop安装在/usr/local/ 目录下)

sudo gedit /usr/local/hadoop/etc/hadoop/hadoop-env.sh

将原本的JAVA_HOME 替换为绝对路径就可以了

#export JAVA_HOME=${JAVA_HOME}

export JAVA_HOME=/usr/lib/jvm/jdk1.8.0_121