搭建好了hadoop环境后，namenode、datanode看着都是正常的。但是当点到browser the file system时，结果报错了，报错的内容是“Failed to retrieve data from /webhdfs/v1/?op=LISTSTATUS: Server Error“.
在解决这个问题上，我走了一些弯路。比如修改hadoop的core-site.xml,hdfs-site.xml。设置文件权限，修改文件目录等。但都不起作用。
后来我看了下hadoop官网的介绍，它支持的jdk的最新版本是11。而我的足迹的jdk的版本是18。
后来我从oracel的官网上下载了jdk的11版本，上传到服务器上，解压缩，重新配置JAVA_HOME环境变量。
修改bashrc文件：
export JAVA_HOME=/root/jdk-11.0.16.1
export PATH=$PATH:$JAVA_HOME/bin:.
然后将hadoop重新启动后，问题解决了。
这个jdk版本的大坑，希望学习大数据的同学跳过这个大坑。
Hadoop Java Versions
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Created by Akira Ajisaka, last modified on Oct 19, 2020Go to start of metadata
Supported Java Versions
Apache Hadoop 3.3 and upper supports Java 8 and Java 11 (runtime only)
Please compile Hadoop with Java 8. Compiling Hadoop with Java 11 is not supported: HADOOP-16795 - Java 11 compile support OPEN
Apache Hadoop from 3.0.x to 3.2.x now supports only Java 8
Apache Hadoop from 2.7.x to 2.10.x support both Java 7 and 8
Supported JDKs/JVMs
Now Apache Hadoop community is using OpenJDK for the build/test/release environment, and that's why OpenJDK should be supported in the community.
https://github.com/apache/hadoop/blob/rel/release-3.2.1/dev-support/docker/Dockerfile#L92
Other jdks/jvms should work well. If you find they don't work as expected, please file a JIRA.
