纪念：站主于 2019 年 10 月完成了此开源实验，并将过程中的所有命令经过整理和注释以后，形成以下教程
软件准备：
在 Hadoop 官网上下载搭建平台所需软件 Hadoop（本次实验使用的是 hadoop-3.2.1.tar.gz）：
http://hadoop.apache.org
正文：
步骤一：硬件环境要求
1) CPU：双核
2) 内存：2G 以上
3) 硬盘：10G 以上
步骤二：系统环境要求
1) 服务器的系统需要是 CentOS Linux 7 版本
2) 服务器系统要配置好可用的软件源
3) 服务器要能 ping 通自己的主机名
步骤三：软件环境要求
3.1 安装 Hadoop 所需的 Java 环境
# yum install java-1.8.0-openjdk-devel
（补充：这里安装 java-openjdk-devel 的版本是 1.8.0）
3.2 显示本机在 Java 环境下所处的角色
# jps
步骤四：安装 Hadoop
4.1 解压 Hadoop 安装包
# tar -xvf hadoop-3.2.1.tar.gz
（补充：这里要安装的 hadoop 版本是 3.2.1）
4.2 创建 Hadoop 的安装目录
# mkdir /usr/local/hadoop
4.3 安装 Hadoop
# mv hadoop-3.2.1/* /usr/local/hadoop
（补充：这里安装的是 hadoop-3.2.1.tar.gz）
4.4 第 1 次启动 Hadoop 会提示报错
/usr/local/hadoop/bin/hadoop
Error: JAVA_HOME is not set and could not be found.
（补充：造成这种原因，主要是他找不到自己的配置文件和自己所需要的配置文件）
4.5 解决第 1 次启动 Hadoop 报错的问题
4.5.1 解决第 1 次启动 Hadoop 报错问题的思路
先确认刚刚安装的 java-1.8.0-openjdk-devel 软件的安装位置，然后再将这个位置写到 Hadoop 的配置文件里
4.5.2 显示 java-1.8.0-openjdk-devel 软件的安装位置
# rpm -ql java-1.8.0-openjdk
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre/bin/policytool
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre/lib/amd64/libawt_xawt.so
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre/lib/amd64/libjawt.so
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre/lib/amd64/libjsoundalsa.so
/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre/lib/amd64/libsplashscreen.so
/usr/share/applications/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64-policytool.desktop
/usr/share/icons/hicolor/16x16/apps/java-1.8.0.png
/usr/share/icons/hicolor/24x24/apps/java-1.8.0.png
/usr/share/icons/hicolor/32x32/apps/java-1.8.0.png
/usr/share/icons/hicolor/48x48/apps/java-1.8.0.png
（补充：可以看出这里是安装目录：/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre）
4.5.3 在 Hadoop 的配置文件里指定 java-openjdk-devel 和 Hadoop 配置文件的安装位置
# vim /usr/local/hadoop/etc/hadoop/hadoop-env.sh
将以下内容：
......
54 # export JAVA_HOME=
......
68 # export HADOOP_CONF_DIR=${HADOOP_HOME}/etc/hadoop
......
修改为：
......
54 export JAVA_HOME="/usr/lib/jvm/java-1.8.0-openjdk-1.8.0.181-7.b13.el7.x86_64/jre"
......
68 export HADOOP_CONF_DIR="/usr/local/hadoop/etc/hadoop"
......
步骤五：启动 Hadoop
# /usr/local/hadoop/bin/hadoop
Usage: hadoop [OPTIONS] SUBCOMMAND [SUBCOMMAND OPTIONS]
or hadoop [OPTIONS] CLASSNAME [CLASSNAME OPTIONS]
where CLASSNAME is a user-provided Java class
OPTIONS is none or any of:
buildpaths attempt to add class files from build tree
--config dir Hadoop config directory
--debug turn on shell script debug mode
--help usage information
hostnames list[,of,host,names] hosts to use in slave mode
hosts filename list of hosts to use in slave mode
loglevel level set the log4j level for this command
workers turn on worker mode
SUBCOMMAND is one of:
Admin Commands:
daemonlog get/set the log level for each daemon
Client Commands:
archive create a Hadoop archive
checknative check native Hadoop and compression libraries availability
classpath prints the class path needed to get the Hadoop jar and the required libraries
conftest validate configuration XML files
credential interact with credential providers
distch distributed metadata changer
distcp copy file or directories recursively
dtutil operations related to delegation tokens
envvars display computed Hadoop environment variables
fs run a generic filesystem user client
gridmix submit a mix of synthetic job, modeling a profiled from production load
jar <jar> run a jar file. NOTE: please use "yarn jar" to launch YARN applications, not this
command.
jnipath prints the java.library.path
kdiag Diagnose Kerberos Problems
kerbname show auth_to_local principal conversion
key manage keys via the KeyProvider
rumenfolder scale a rumen input trace
rumentrace convert logs into a rumen trace
s3guard manage metadata on S3
trace view and modify Hadoop tracing settings
version print the version
Daemon Commands:
kms run KMS, the Key Management Server
SUBCOMMAND may print help when invoked w/o parameters or with -h.
