一、情景 

  公司刚上几台Linux，现在要把主机之间都能远程ssh免密码登陆。


二、原理

        很简单，使用ssh-keygen 在主机A上生成private和public密钥，将生成的public密钥拷贝到远程机器主机B上后,就可以使用ssh命令无需密码登录到另外一台机器主机B上。


三、步骤


  主机A：

 1、 生成公钥和私钥文件id_rsa和id_rsa.pub （敲3下回车即可）            

[root@bogon ~]# ssh-keygen -t rsa

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:

67:da:0d:79:e0:d6:2b:cd:7d:22:af:51:7e:9c:75:fe root@bogon

The key's randomart p_w_picpath is:

+--[ RSA 2048]----+

|                 |

|                 |

|          .      |

|         . +     |

|        S B o . o|

|         * * = o+|

|        . o B +.=|

|           . + +.|

|            ... E|

+-----------------+


2、ssh-cop-id命令会将指定的公钥文件复制到远程计算机

[root@bogon ~]#  ssh-copy-id -i ~/.ssh/id_rsa.pub [email protected]

The authenticity of host '10.1.250.166 (10.1.250.166)' can't be established.

RSA key fingerprint is c8:9d:6d:92:55:77:3d:3e:af:f5:cb:18:80:5a:47:93.

Are you sure you want to continue connecting (yes/no)? yes

Warning: Permanently added '10.1.250.166' (RSA) to the list of known hosts.

reverse mapping checking getaddrinfo for bogon [10.1.250.166] failed - POSSIBLE BREAK-IN ATTEMPT!

[email protected]'s password: <主机B的登陆密码>    

Now try logging into the machine, with "ssh '[email protected]'", and check in:


  .ssh/authorized_keys


to make sure we haven't added extra keys that you weren't expecting.


3、然后ssh登陆主机B验证是否需要密码


[root@localhost ~]# ssh 10.1.250.166

reverse mapping checking getaddrinfo for bogon [10.1.250.166] failed - POSSIBLE BREAK-IN ATTEMPT!

Last login: Wed Oct 21 10:05:39 2015 from 10.1.250.141

[root@bogon ~]# 


4、登陆成功后，我们需要在主机B也做下以上3步，这样就可以相互免密码ssh登陆。（如果有多台主机，每台主机都做下相同操作，以方便以后管理）。


5、权限问题

   建议用其他用户做ssh登陆的话，调整目录文件权限

   设置authorized_keys权限

   

chmod 644 authorized_keys


   设置.ssh目录权限

   

chmod 700 -R .ssh


6、要保证.ssh和authorized_keys都只有用户自己有写权限。否则验证无效。