【此篇純屬自己的筆記記錄，無實際幫助價值】
強烈建議參考官方文件http://hadoop.apache.org/docs/current/hadoop-project-dist/hadoop-common/SingleCluster.html 來安裝hadoop。搜尋引擎搜出來的很多內容，都是找不到內容的，比如hadoop解壓後的目錄下根本沒有conf檔案夾了。
剛開始接觸hadoop不久，又在另外一臺電腦上搭建一次hadoop環境。
按照http://www.cnblogs.com/kinglau/p/3794433.html來處理（下面這幾個步驟參考這個網頁的）
1.建立hadoop使用者和組sudo addgroup hadoop

2.建立hadoop使用者 sudo adduser -ingroup hadoop hadoop
3.為hadoop使用者新增許可權sudo vim /etc/sudoers

# User privilege specification
root    ALL=(ALL:ALL) ALL
hadoop  ALL=(ALL:ALL) ALL

4.安裝ssh sudo apt-get install ssh
安裝pdsh sudo apt-get install pdsh
5.檢視服務是否啟動 ps -e | grep ssh
6.設定免密碼登入，生成私鑰和公鑰ssh-keygen -t rsa -P ""

7.將公鑰追加到authorized_keys中，它使用者儲存所有允許以當前使用者身份登入到ssh客戶端使用者的公鑰內容。cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
8.到了後面，發現是使用hadoop重新登入系統，然後再次安裝jdk等環境。由於我目前的使用者不是root，已經安裝了jdk等環境，就不想按照其步驟繼續。
直接將解壓之後的hadoop資料夾移動到/usr/lib/目錄下，然後修改~/.bashrc檔案內容。最後使用WordCount示例。

HP-Pavilion-g4-Notebook-PC:/usr/lib/hadoop-
 
2.8.0$ sudo mv ~/Downloads/hadoop-2.8.0/ /usr/lib/
HP-Pavilion-g4-Notebook-PC:/usr/lib/hadoop-2.8.0$ chmod 775 /usr/lib/hadoop-2.8.0/
HP-Pavilion-g4-Notebook-PC:/usr/lib/hadoop-2.8.0$ vim ~/.bashrc
HP-Pavilion-g4-Notebook-PC:/usr/lib/hadoop-2.8.0$ source ~/.bashrc
HP-Pavilion-g4-Notebook-PC:/usr/lib/hadoop-2.8.0$ bin/hadoop jar share/hadoop/mapreduce/sources/hadoop-mapreduce-examples-2.8.0-sources.jar org.apache.hadoop.examples.WordCount ~/Documents/feature/negative/negative_Special_DR_Tag_result.txt output
HP-Pavilion-g4-Notebook-PC:/usr/lib/hadoop-2.8.0$ cat output/*

~/.bashrc內容

export JAVA_HOME=/usr/lib/jvm/java
export JRE_HOME=${JAVA_HOME}/jre
export CLASSPATH=.:${JAVA_HOME}/lib:${JRE_HOME}/lib
export PATH=${JAVA_HOME}/bin:$PATH

export SCALA_HOME=/usr/lib/scala-2.12.1
export PATH=$PATH:${SCALA_HOME}/bin

export SPARK_HOME=/usr/lib/spark-2.1.0-bin-hadoop2.7
export PATH=$PATH:${SPARK_HOME}/bin

export MAVEN_HOME=/usr/lib/apache-maven-3.3.9
export PATH=$PATH:${MAVEN_HOME}/bin

#set weka enviroment
export WEKA_HOME=/usr/weka
export CLASSPATH=$CLASSPATH:$WEKA_HOME/weka.jar

#set hadoop enviroment
export HADOOP_HOME=/usr/lib/hadoop-2.8.0
export path=$PATH:${HADOOP_HOME}/bin:${HADOOP_HOME}/sbin

vim /usr/lib/hadoop-2.8.0/etc/hadoop/hadoop-env.sh

# set to the root of your Java installation
export JAVA_HOME=/usr/lib/jvm/java

注意修改這個JAVA_HOME路徑，否則在後面使用時候，會報錯

HP-Pavilion-g4-Notebook-PC:/usr/lib/hadoop-2.8.0$ sbin/start-dfs.sh
Starting namenodes on [localhost]
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 secondary namenodes [0.0.0.0]
The authenticity of host '0.0.0.0 (0.0.0.0)' can't be established.
ECDSA key fingerprint is 7f:77:9e:35:fe:21:22:6f:dd:4c:20:27:16:d1:43:37.
Are you sure you want to continue connecting (yes/no)?