2.修改/etc/hosts文件 /安装SSH、配置SSH无密码登陆（全程切换到hadoop用户下操作）
修改/etc/hosts文件
sudo gedit /etc/hosts
127.0.0.1 localhost
192.168.222.129 master 下面分别对应三个机器的IP地址，用ifconfig查看
192.168.222.130 slave1
192.168.222.131 slave2
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
测试是否能ping通
ping master/slave1/slave2==========
分别给3台机器都创建hadoop用户，方便进行管理
二、 建立hadoop运行帐号
即为hadoop集群专门设置一个用户组及用户
(1)创建hadoop用户组
(2)创建hadoop用户
sudo adduser -ingroup hadoop hadoop
回车后会提示输入新的UNIX密码，这是新建用户hadoop的密码，输入回车即可。
最后确认信息是否正确，如果没问题，输入 Y，回车即可。
(3)为hadoop用户添加权限(给hadoop用户赋予和root用户同样的权限)
输入：
sudo gedit /etc/sudoers
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
================================================
用新增加的hadoop用户登录Ubuntu系统,进行SSH的配置
================================================
配置ssh免密码登录
hadoop工作时，各节点要相互通讯，正常情况下linux之间通讯要提供用户名、密码（目的是保证通讯安全），如果
需要人工干预输入密码，显然不方便，做这一步的目的，是让各节点能自动通过安全认证，不影响正常通讯。
安装ssh: sudo apt-get install openssh-server
安装完成后，启动服务:sudo /etc/init.d/ssh start
查看服务是否正确启动：ps -e | grep ssh一.使用SSH使每一台机器免密码登录自己本机
//下面以mster机器为例：
1.使登录身份始终是hadoop，操作目录始终是/home/master
master@master:~$ su hadoop #切换成hadoop(以hadoop身份登录到系统)
hadoop@master:~$cd /home/hadoop(进入个人主目录，默认为/home/hadoop)
2.生成公钥私钥id_rsa id_rsa.pub
hadoop@master:~$ ssh-keygen -t rsa -P '' (注：最后是二个单引号，生成公钥私钥)
Generating public/private rsa key pair.
Enter file in which to save the key (/home/hadoop/.ssh/id_rsa):
Created directory '/home/hadoop/.ssh'.
Your identification has been saved in /home/hadoop/.ssh/id_rsa.
Your public key has been saved in /home/hadoop/.ssh/id_rsa.pub.
The key fingerprint is:
cd:67:f5:0f:15:a1:42:ad:7a:29:78:3b:ca:8c:3a:b7 hadoop@slave1
The key's randomart image is:
+--[ RSA 2048]----+
| .. o.|
| . .. .|
| .... .|
| o ... o |
| S + + . .|
| . + = ..|
| . + .|
| . .+ o |
| .+E.+. . |
+-----------------+
解释：以rsa算法，生成公钥、私钥对，-P ''表示空密码。该命令
运行完后，会在个人主目录/home/hadoop下生成.ssh目录，里面会
有二个文件id_rsa（私钥） ,id_rsa.pub(公钥)，即：
hadoop@master:~$ ls .ssh #查看是否生成公钥私钥
id_rsa id_rsa.pub
3.导入公钥
hadoop@master:cat .ssh/id_rsa.pub >> .ssh/authorized_keys
解释：会在个人主目录/home/hadoop/.ssh目录下生成authorized_keys，即
hadoop@master:~$ ls .ssh #查看是否生成authorized_keys
authorized_keys id_rsa id_rsa.pub
4.修改文件权限
hadoop@master:chmod 600 .ssh/authorized_keys
5.进行SSH测试是否能免密码连接本机
执行完以后，可以在本机上测试下，用ssh连接自己，即：ssh localhost (或ssh master)
【注解】废话不多说，直接上下面中3个中括号中的命令
【hadoop@master:~$ ssh localhost】 #连接自己
The authenticity of host 'localhost (127.0.0.1)' can't be established.
ECDSA key fingerprint is d5:f7:47:44:7b:9f:55:ac:e7:ed:6c:8d:f6:98:68:72.
Are you sure you want to continue connecting (yes/no)? yes #输入yes
Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)
* Documentation: https://help.ubuntu.com/
New release '16.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.
【hadoop@master:~$ exit】 #连接成功后，退出exit
注销
Connection to localhost closed.
【hadoop@master:~$ ssh localhost】 #重新链接，不需要密码，此时成功配置了master机器的SSH
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)
* Documentation: https://help.ubuntu.com/
281 packages can be updated.
193 updates are security updates.
New release '16.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Fri Aug 11 10:22:27 2017 from localhost
hadoop@master:~$
【终于】
到此位置，成功搞定一台机器：master，下面我们再进行slave1，slave2机器的SSH免密码登录的配置。（配置方法同上）二. 将slave公钥文件复制到master（只操作slave机器，不操作master）
a)用scp命令，把公钥文件发放给master（即：刚才已经搞定的那台机器）
#在slave1上：
scp .ssh/id_rsa.pub hadoop@master:/home/hadoop/id_rsa_01.pub
#在slave2上：
scp .ssh/id_rsa.pub hadoop@master:/home/hadoop/id_rsa_02.pub
b)这二行执行完后，回到master中，查看下/home/hadoop目录，应该有二个新文
件id_rsa_01.pub、id_rsa_02.pub，然后在master上，导入这二个公钥
cat id_rsa_01.pub >> .ssh/authorized_keys
cat id_rsa_02.pub >> .ssh/authorized_keys
这样，master这台机器就有所有3台机器的公钥了。
三. 将master上的“最全”公钥，复制到其它机器slave1.slave2
a) 继续保持在master上，
scp .ssh/authorized_keys hadoop@slave1:/home/hadoop/.ssh/authorized_keys
scp .ssh/authorized_keys hadoop@slave2:/home/hadoop/.ssh/authorized_keys
b) 修改其它机器上authorized_keys文件的权限
slave1以及slave2机器上，均执行命令
chmod 600 .ssh/authorized_keys
四. 验证能否通过SSH无密码连接其他机器
在每个虚拟机上，均用 ssh 其它机器的hostname 验证下，如果能正常无密码连接成功，表示ok
以master机器，连接slave1，slave2机器为例：
（1）切换到hadoop用户
master@master:~$ su hadoop
（2）测试无密码连接slave1
hadoop@master:/home/master$ ssh slave1
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)
* Documentation: https://help.ubuntu.com/
281 packages can be updated.
193 updates are security updates.
New release '16.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Fri Aug 11 11:02:00 2017 from slave2
（3）测试无密码连接slave2
hadoop@slave1:~$ ssh slave2
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)
* Documentation: https://help.ubuntu.com/
281 packages can be updated.
193 updates are security updates.
New release '16.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Fri Aug 11 11:02:11 2017 from slave2
【发现】master可以无密码连接slave1，slave2，同理，下面
分别进行测试slave1，slave2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
【重点】非常容易犯的错误
配置SSH成功后，每次都要"先切换到hadoop用户"下，才可以SSH成功
（1）切换到用户hadoop
master@master:~$ su hadoop
密码：
（2）SSH本机器
hadoop@master:/home/master$ ssh master
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)
* Documentation: https://help.ubuntu.com/
New release '16.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Fri Aug 11 18:12:54 2017 from master
hadoop@master:~$
（3）SSH slave1机器
hadoop@master:~$ ssh slave1
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)
* Documentation: https://help.ubuntu.com/
New release '16.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Fri Aug 11 18:16:14 2017 from master
hadoop@slave1:~$
（3）SSH slave2机器
hadoop@slave1:~$ ssh slave2
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)
* Documentation: https://help.ubuntu.com/
New release '16.04.3 LTS' available.
Run 'do-release-upgrade' to upgrade to it.
Last login: Fri Aug 11 17:35:47 2017 from slave1
hadoop@slave2:~$
[小结]
小结：该步骤非常重要，主要思路是在各节点上生成公钥、私钥，然后将公钥发放其它所有节点。RSA算法是非
对称加密算法，仅公布“公钥”，只要私钥不外泄，还是不能解密的，所以安全性依然有保障。
如果本步骤失败，根据我个人经验，多半是权限问题，请检查hadoop是否具有足够权限，建议将hadoop加
入sudoers列表及root用户组。另外,这里也整理了一些SSH免密码设置失败的原因,请移步 ssh 免密码设置失败原因总结Hadoop集群安装配置教程_Hadoop2.6.0_Ubuntu/CentOShttp://dblab.xmu.edu.cn/blog/285/