1、新版本2.4.1中，profile/hadoop-env.sh中均己设置 JAVA_HOME，  java -version也正常。

启动时报错：

[root@nn ~]# start-all.sh

Starting namenodes on []

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

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

...

starting yarn daemons
starting resourcemanager, logging to /home/lihanhui/open-source/hadoop-2.1.0-beta/logs/yarn-admin-resourcemanager-localhost.out
localhost: Error: JAVA_HOME is not set and could not be found

直接命令行执行export JAVA_HOME=/PATH/TO/JDK也无法解决问题：

最终在   hadoop-2.4.1/etc/hadoop/libexec/hadoop-config.sh  这个配置文件中搜到报错信息“JAVA_HOME is not set and could not be found”

于是在这个配置文件中，  export JAVA_HOME=/PATH/JDK

问题得己解决、

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HADOOP报错，随笔