本文主要講述了LINUX環境如何配置SSH信任，配置SSH信任的目地是，SSH到目標機器上時，不用再輸入密碼。


環境: 兩臺linux的機器，主機名分別為db2a、db2b，IP地址分別為192.168.187.141、192.168.187.142，都有一個名為qingsong的使用者
$ cat /etc/hosts
127.0.0.1       localhost
192.168.187.141 db2a
192.168.187.142 db2b

具體步驟：

1. 沒有配置ssh時，從db2a SSH到db2b時，每次都要輸入密碼：
[email protected]:~$ ssh db2b
The authenticity of host 'db2b (192.168.187.142)' can't be established.
ECDSA key fingerprint is f2:94:73:e7:8e:6c:c4:50:aa:54:9c:15:57:61:bb:e6.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'db2b,192.168.187.142' (ECDSA) to the list of known hosts.
[email protected]'s password: <--輸入密碼
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)

 * Documentation:  https://help.ubuntu.com/
New release '16.04.2 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

Last login: Sat Jun 24 07:57:47 2017 from 192.168.187.1

[email protected]db2b:~$  <--輸入密碼之後，成功

[email protected]:~$ exit
logout
Connection to db2b closed.

[email protected]:~$ ssh db2b
[email protected]'s password: <--輸入密碼
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)

 * Documentation:  https://help.ubuntu.com/
New release '16.04.2 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

Last login: Sat Jun 24 08:03:34 2017 from db2a


2. 配置SSH信任 

看home目錄下有沒有名為 '.ssh'的資料夾，如果沒有，新建一個，兩個機器上執行的命令是相同的：

db2a上：

[email protected]:~$ cd .ssh

[email protected]:~/.ssh$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/qingsong/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/qingsong/.ssh/id_rsa.
Your public key has been saved in /home/qingsong/.ssh/id_rsa.pub.
The key fingerprint is:
a6:58:05:69:29:0c:a6:a3:ec:3d:54:2f:0a:b9:12:28 [email protected]
The key's randomart image is:
+--[ RSA 2048]----+
|  oo  .o         |
| o  o +.         |
|o    +  .        |
|+.. . ..         |
|E+ . ...S        |
|o.= .o.o         |
|.o +. .          |
|.   .            |
|                 |
+-----------------+

[email protected]:~/.ssh$ ls
id_rsa  id_rsa.pub  known_hosts

[email protected]:~/.ssh$ touch authorized_keys

[email protected]:~/.ssh$ chmod 600 authorized_keys

db2b上：
[email protected]:~$ cd .ssh
[email protected]:~/.ssh$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/qingsong/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/qingsong/.ssh/id_rsa.
Your public key has been saved in /home/qingsong/.ssh/id_rsa.pub.
The key fingerprint is:
76:1a:39:eb:97:9b:31:28:ab:06:1f:ef:e9:7a:35:49 [email protected]
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|                 |
|                 |
|        E.       |
|       .S..      |
|  . .  .+B       |
|   o o..+.o.     |
|    o o=  o+     |
|   .o*= ..o.     |
+-----------------+
[email protected]:~/.ssh$ ls
id_rsa  id_rsa.pub

[email protected]:~/.ssh$ touch authorized_keys

[email protected]:~/.ssh$ chmod 600 authorized_keys

這時候，只要把db2a中id_rsa.pub的內容追加到db2b的authorized_keys檔案裡，就可以實現使用者qingsong從db2a機SSH到db2b時，不用輸入密碼：

db2a上：
[email protected]:~/.ssh$ cat id_rsa.pub 
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDsI4m6nTRdaxviBLN9L8DONFj6Y3WUNzBgJsYKNfDfA/y+6ofF5eUgka2cJYeq06/0f+k7OeC4nJZL+pdcG5Syu20berO1KbIqE6hAZ8eUgbaoteR2/v1eySphV/kcus7NBOw611CKMLD1Q9sWLDsHqtZIlUdlnAX8EMAkwJImBuyLPYesOu/mejn6U474TUMS5WxfXpcoBPDTFvarZWLE2yhg6t//WDiuuileXtP+9T/zWBDyZmJSmc+EhnwvHqjCyylrRHHkks1B3ufYtzBM1HGt/MJKcOitkGshLJFHXam+ovNLU8D46RymZmOJOMMxxEIHMvzgz29URvYCRHsb [email protected]

db2b上：
[email protected]:~/.ssh$ echo "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDsI4m6nTRdaxviBLN9L8DONFj6Y3WUNzBgJsYKNfDfA/y+6ofF5eUgka2cJYeq06/0f+k7OeC4nJZL+pdcG5Syu20berO1KbIqE6hAZ8eUgbaoteR2/v1eySphV/kcus7NBOw611CKMLD1Q9sWLDsHqtZIlUdlnAX8EMAkwJImBuyLPYesOu/mejn6U474TUMS5WxfXpcoBPDTFvarZWLE2yhg6t//WDiuuileXtP+9T/zWBDyZmJSmc+EhnwvHqjCyylrRHHkks1B3ufYtzBM1HGt/MJKcOitkGshLJFHXam+ovNLU8D46RymZmOJOMMxxEIHMvzgz29URvYCRHsb [email protected]" >> authorized_keys 

db2a上：
[email protected]:~/.ssh$ ssh db2b
Welcome to Ubuntu 14.04.5 LTS (GNU/Linux 4.4.0-31-generic x86_64)

 * Documentation:  https://help.ubuntu.com/
New release '16.04.2 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

Last login: Sat Jun 24 08:05:16 2017 from db2a

可以看到，ssh到db2b時就不用輸入密碼了。

同理，

如果想要使用者qingsong從db2b上SSH到db2a上時免密，只需要把db2b上的id_rsa.pub裡內容追加到db2a的authorized_keys裡；

如果想要SSH到本機免密（比如db2a到db2a)，那麼只需要把自己id_rsa.pub的內容追加到自己的authorized_keys裡。

雙向免密都配置完之後，可以測試下：

db2a到本機：
[email protected]:~/.ssh$ ssh db2a date
Sat Jun 24 08:37:01 PDT 2017

db2a到db2b：
[email protected]:~/.ssh$ ssh db2b date
Sat Jun 24 08:37:06 PDT 2017

db2b到本機：
[email protected]:~/.ssh$ ssh db2b date
Sat Jun 24 08:37:27 PDT 2017

db2b到db2a：
[email protected]:~/.ssh$ ssh db2a date
Sat Jun 24 08:37:33 PDT 2017