操作步驟：

1.主機A

生成公鑰id_rsa.pub文件並導出該文件

root@mytest:~# ssh-keygen 
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): 
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.
The key fingerprint is:
7e:0f:dc:05:2e:d3:e0:24:c0:5f:fe:cf:e9:7a:f7:49 root@mytest
The key‘s randomart image is:
+--[ RSA 2048]----+
|     ..          |
|      ..  .      |
|       ..oo .    |
|        .+.+ .   |
|        S +.o .  |
|       . . +..   |
|        . + .o E |
|         . o  * o|
|            o+.oo|
+-----------------+
root@mytest:
 
~# sz /root/.ssh/id_rsa.pub 

這步之後也可以通過以下步驟直接實現公鑰認證（但是需要知道主機B用戶danny的密碼）

# ssh-copy-id -i /root/.ssh/id_rsa.pub danny@12.1.1.2
danny@12.1.1.2‘s password:      //輸入主機B用戶danny的登錄密碼

2.主機B

得到id_rsa.pub文件，創建用戶danny，並在該用戶家目錄創建.ssh文件夾和其文件下的遠程認證文件authorized_keys

[root@B danny]# mkdir .ssh
[root@B danny]# cd .
 
ssh/
[root@B .ssh]# touch authorized_keys
[root@B .ssh]# ls
authorized_keys
[root@B .ssh]# cat /home/danny/id_rsa.pub >authorized_keys

主機A登錄主機B

root@mytest:/# ssh danny@IP_B

從主機A得到id_rsa.pub文件，在主機B創建用戶danny加入該文件，實現主機A免密登錄主機B