详解ssh免密码登录配置方法（图示加命令）

首先，说明一下我们要做的是，servera 服务器的 usera 用户免密码登录 serverb 服务器的 userb用户。

我们先使用usera 登录 servera 服务器

[root@servera ~]# su - usera
[usera@servera ~]$ pwd
/home/usera

然后在servera上生成密钥对

[usera@servera ~]$ ssh-keygen -t rsa
generating public/private rsa key pair.
enter file in which to save the key (/home/usera/.ssh/id_rsa): 
created directory '/home/usera/.ssh'.
enter passphrase (empty for no passphrase): 
enter same passphrase again: 
your identification has been saved in /home/usera/.ssh/id_rsa.
your public key has been saved in /home/usera/.ssh/id_rsa.pub.
the key fingerprint is:
39:f2:fc:70:ef:e9:bd:05:40:6e:64:b0:99:56:6e:01 usera@servera
the key's randomart image is:
+--[ rsa 2048]----+
|     eo*  |
|      @ .  |
|     = *  |
|     o o .  |
|   . s   . |
|    + .   . |
|    + .   .|
|     + . o . |
|     .o= o. |
+-----------------+

此时会在/home/usera/.ssh目录下生成密钥对

[usera@servera ~]$ ls -la .ssh
总用量 16
drwx------ 2 usera usera 4096 8月 24 09:22 .
drwxrwx--- 12 usera usera 4096 8月 24 09:22 ..
-rw------- 1 usera usera 1675 8月 24 09:22 id_rsa
-rw-r--r-- 1 usera usera 399 8月 24 09:22 id_rsa.pub

然后将公钥上传到serverb 服务器的，并以userb用户登录

[usera@portalweb1 ~]$ ssh-copy-id userb@10.124.84.20
the authenticity of host '10.124.84.20 (10.124.84.20)' can't be established.
rsa key fingerprint is f0:1c:05:40:d3:71:31:61:b6:ad:7c:c2:f0:85:3c:cf.
are you sure you want to continue connecting (yes/no)? yes
warning: permanently added '10.124.84.20' (rsa) to the list of known hosts.
userb@10.124.84.29's password: 
now try logging into the machine, with "ssh 'userb@10.124.84.20'", and check in:
 
 .ssh/authorized_keys
 
to make sure we haven't added extra keys that you weren't expecting.

这个时候usera的公钥文件内容会追加写入到userb的 .ssh/authorized_keys 文件中

[usera@servera ~]$ cat .ssh/id_rsa.pub 
ssh-rsa aaaab3nzac1yc2eaaaabiwaaaqea2dpxfvifkpswsbuspcuwred/mftwpdeerhlwaxnixgixlvhus9qnavepzocvpbzwhade88klpkr5xev6m5rschxxmxj1ie5vblrrs0ndjf8ajclqptdguyerplybonrfftqgxac/ximmbyhecti0vnujlvet0pprj7bqmmxr/2lnlhifxkzcxgzzqhgqybqqk/rqweuyaiumvuim8ssk/rdg8hl/n0exjh9jv8h17od4htnfkv5+zrfbki5vfsetffn49q4xa7sb9o7z6scvrhjcmw3gbzzgyupsj0wkqdtw2un0nh4ugqo7jfyilrvztwim7p6ygsi7vma/vrp0aw== usera@servera

查看serverb服务器userb用户下的 ~/.ssh/authorized_keys文件，内容是一样的，此处我就不粘贴图片了。

[userb@serverb ~]$ cat .ssh/authorized_keys 
ssh-rsa aaaab3nzac1yc2eaaaabiwaaaqea2dpxfvifkpswsbuspcuwred/mftwpdeerhlwaxnixgixlvhus9qnavepzocvpbzwhade88klpkr5xev6m5rschxxmxj1ie5vblrrs0ndjf8ajclqptdguyerplybonrfftqgxac/ximmbyhecti0vnujlvet0pprj7bqmmxr/2lnlhifxkzcxgzzqhgqybqqk/rqweuyaiumvuim8ssk/rdg8hl/n0exjh9jv8h17od4htnfkv5+zrfbki5vfsetffn49q4xa7sb9o7z6scvrhjcmw3gbzzgyupsj0wkqdtw2un0nh4ugqo7jfyilrvztwim7p6ygsi7vma/vrp0aw== usera@servera

另外我们要注意，.ssh目录的权限为700，其下文件authorized_keys和私钥的权限为600。否则会因为权限问题导致无法免密码登录。我们可以看到登陆后会有known_hosts文件生成。

[useb@serverb ~]$ ls -la .ssh
total 24
drwx------. 2 useb useb 4096 jul 27 16:13 .
drwx------. 35 useb useb 4096 aug 24 09:18 ..
-rw-------  1 useb useb 796 aug 24 09:24 authorized_keys
-rw-------  1 useb useb 1675 jul 27 16:09 id_rsa
-rw-r--r--  1 useb useb 397 jul 27 16:09 id_rsa.pub
-rw-r--r--  1 useb useb 1183 aug 11 13:57 known_hosts

这样做完之后我们就可以免密码登录了

[usera@servera ~]$ ssh userb@10.124.84.20

另外，将公钥拷贝到服务器的~/.ssh/authorized_keys文件中方法有如下几种：

1、将公钥通过scp拷贝到服务器上，然后追加到~/.ssh/authorized_keys文件中，这种方式比较麻烦。scp -p 22 ~/.ssh/id_rsa.pub user@host:~/。

2、通过ssh-copy-id程序，就是我演示的方法，ssh-copyid user@host即可

3、可以通过cat ~/.ssh/id_rsa.pub | ssh -p 22 user@host ‘cat >> ~/.ssh/authorized_keys'，这个也是比较常用的方法，因为可以更改端口号。

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