Hadoop集群包含1個主節點和3個從節點，需要實現各節點之間的免密碼登錄，下面介紹具體的實現方法。

一、Hadoop集群環境

二、免密登錄原理

每臺主機authorized_keys文件里面包含的主機（ssh密鑰），該主機都能無密碼登錄，所以只要每臺主機的authorized_keys文件里面都放入其他主機（需要無密碼登錄的主機）的ssh密鑰就行了。

 三、實現方法

1. 配置每個節點的hosts文件

#vim /etc/hosts
1 192.168.44.3 hadoop01
2 192.168.44.4 hadoop02
3 192.168.44.5 hadoop03
4 192.168.44.6 hadoop04

2. 每個節點生成ssh密鑰

[root@hadoop01 ~]# ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory ‘/root/.ssh’.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
…………………

[root@hadoop01 .ssh]# ls
id_rsa  id_rsa.pub

執行命令后會在~目錄下生成.ssh文件夾，里面包含id_rsa和id_rsa.pub兩個文件。

注：使用ssh-keygen -t rsa -P ” -f ~/.ssh/id_rsa命令可避免上述交互式操作。

3. 在主節點上將公鑰拷到一個特定文件authorized_keys中。

[root@hadoop01 ~]# cd .ssh
[root@hadoop01 .ssh]# ls
id_rsa  id_rsa.pub
[root@hadoop01 .ssh]# cp id_rsa.pub authorized_keys
[root@hadoop01 .ssh]# ls
authorized_keys  id_rsa  id_rsa.pub

4. 將authorized_keys文件拷到下一個節點，并將該節點的ssh密鑰id_rsa.pub加入該文件中。

#在hadoop01上使用scp命令實現遠程文件拷貝
[root@hadoop01 .ssh]# scp authorized_keys  root@hadoop02:/root/.ssh/
The authenticity of host ‘hadoop02 (192.168.44.11)’ can’t be established.
ECDSA key fingerprint is SHA256:MyB1zs0E3J/fm8pC0AN8ycsgEIBNHtUqd9xS0WAyv3s.
ECDSA key fingerprint is MD5:88:48:3a:ba:3e:14:a7:d7:86:f6:51:74:00:10:f9:00.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added ‘hadoop02,192.168.44.11’ (ECDSA) to the list of known hosts.
root@hadoop02’s password:
authorized_keys                                                                100%  395  306.2KB/s  00:00   

#登錄hadoop02主機

[root@hadoop02 ~]# cd .ssh/
[root@hadoop02 .ssh]# ls
authorized_keys id_rsa id_rsa.pub
[root@hadoop02 .ssh]# cat id_rsa.pub >> authorized_keys #使用cat追加方式

5. 重復第4步的操作，依次將hadoop03、hadoop04節點的ssh密鑰加入到authorized_keys文件中，并將hadoop04節點生成的authorized_keys文件拷貝到其他三個節點（hadoop01、hadoop02、hadoop03）即可。

#登錄hadoop03主機，將ssh密鑰加入authorized_keys文件中
[root@hadoop03 .ssh]# cat id_rsa.pub >> authorized_keys
[root@hadoop03 .ssh]# scp authorized_keys root@hadoop04:/root/.ssh/

#登錄hadoop04主機，將ssh密鑰加入authorized_keys文件中
[root@hadoop04 .ssh]# cat id_rsa.pub >> authorized_keys

#將最后生成的authorized_keys文件分別拷貝到hadoop01、hadoop02和hadoop03
[root@hadoop04 .ssh]# scp authorized_keys root@hadoop01:/root/.ssh/
[root@hadoop04 .ssh]# scp authorized_keys root@hadoop02:/root/.ssh/
[root@hadoop04 .ssh]# scp authorized_keys root@hadoop03:/root/.ssh/

6. 驗證免密登錄

使用ssh 用戶名@節點名或ssh ip地址命令驗證免密碼登錄。

[root@hadoop01 .ssh]# ssh root@hadoop02
Last login: Tue Feb 12 03:59:46 2019 from 192.168.44.1

[root@hadoop02 .ssh]# ssh root@hadoop01
Last login: Tue Feb 12 21:27:24 2019 from hadoop04

[root@hadoop03 .ssh]# ssh root@hadoop04
Last login: Tue Feb 12 04:00:47 2019 from 192.168.44.1

[root@hadoop04 .ssh]# ssh root@hadoop01
Last login: Tue Feb 12 21:26:44 2019 from hadoop02

在 Linux Ubuntu 18.04/18.10上安裝Hadoop圖文詳解  http://www.wangcai868.com/Linux/2018-11/155282.htm

CentOS 7 下搭建Hadoop 2.9 分布式集群  http://www.wangcai868.com/Linux/2018-11/155328.htm