Linux实现免密登录的配置方法

需求描述：
192.168.31.10 服务器的yunwei账号，想要免密登陆到 192.168.31.15 服务器上。
直接 ssh root@192.168.31.15 这样登陆，不用输入密码。

实现：
1、在10机器上，创建运维账号。

[root@docker01 ~]# id yunwei                检查yunwei账号是否存在
id: yunwei: no such user
[root@docker01 ~]# useradd yunwei            创建yunwei账号
[root@docker01 ~]# su - yunwei                切换到yunwei账号
[yunwei@docker01 ~]$ pwd
/home/yunwei

2、在yunwei账号下创建密钥

[yunwei@docker01 ~]$ ssh-keygen        创建密钥，一路回车
Generating public/private rsa key pair.
Enter file in which to save the key (/home/yunwei/.ssh/id_rsa):
Created directory '/home/yunwei/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/yunwei/.ssh/id_rsa.
Your public key has been saved in /home/yunwei/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:kLXaRvzgGOqF62RyGWKGUekspD39l0pudQBt1MQp3NU yunwei@docker01
The key's randomart image is:
+---[RSA 2048]----+
|  ..   +o=.o..   |
| o.   .+=.=   E  |
|++ .  +o=.       |
|oo= .o O.o       |
|..+.+.+ So.      |
| o o =o.+ .      |
|  . Bo + .       |
|   *  +          |
|    ..           |
+----[SHA256]-----+
检查密钥是否创建成功
[yunwei@docker01 ~]$ pwd
/home/yunwei
[yunwei@docker01 ~]$ ll -a
total 12
drwx------.  5 yunwei yunwei 103 Mar 25 23:18 .
drwxr-xr-x. 16 root   root   177 Mar 25 23:17 ..
-rw-r--r--.  1 yunwei yunwei  18 Mar 31  2020 .bash_logout
-rw-r--r--.  1 yunwei yunwei 193 Mar 31  2020 .bash_profile
-rw-r--r--.  1 yunwei yunwei 231 Mar 31  2020 .bashrc
drwxrwxr-x.  3 yunwei yunwei  18 Mar 25 23:17 .cache
drwxrwxr-x.  3 yunwei yunwei  18 Mar 25 23:17 .config
drwx------.  2 yunwei yunwei  38 Mar 25 23:18 .ssh
[yunwei@docker01 ~]$ cd .ssh/
[yunwei@docker01 .ssh]$ ls
id_rsa  id_rsa.pub

3、复制密钥到15服务器

[yunwei@docker01 .ssh]$ ssh-copy-id root@192.168.31.15        复制密钥到15机器
/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/yunwei/.ssh/id_rsa.pub"
The authenticity of host '192.168.31.15 (192.168.31.15)' can't be established.
ECDSA key fingerprint is SHA256:v3zhW/rvSt+T7QfAnIDIiHhbALRLNiLzl8Hg3TAZQCA.
ECDSA key fingerprint is MD5:cf:b8:e1:f6:a5:61:60:f0:77:aa:f3:76:ab:d2:ce:9b.
Are you sure you want to continue connecting (yes/no)? yes
/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
root@192.168.31.15's password:
Number of key(s) added: 1
Now try logging into the machine, with:   "ssh 'root@192.168.31.15'"
and check to make sure that only the key(s) you wanted were added.

4、验证免密登陆

[yunwei@docker01 .ssh]$ ssh root@192.168.31.15
Last login: Sun Mar 26 11:21:02 2023 from 192.168.31.1

补充：优化密钥创建方式，免交互创建密钥

[yunwei@docker01 .ssh]$ ssh-keygen -P '' -f id_rsa        免交互方式，创建密钥
Generating public/private rsa key pair.
Your identification has been saved in id_rsa.
Your public key has been saved in id_rsa.pub.
The key fingerprint is:
SHA256:hXuSBtV1o1D1PfIyG/+iC1IFnZh8Q3NGf5eiuQ8IExQ yunwei@docker01
The key's randomart image is:
+---[RSA 2048]----+
|       EoooB=+B  |
|      .. .=o=* +o|
|      ... ..o+ o*|
|       ..+ .o + +|
|       oS oo + . |
|       .o+. . *  |
|        ...o . . |
|         . .o . .|
|            o+ ..|
+----[SHA256]-----+
[yunwei@docker01 .ssh]$ ls
id_rsa  id_rsa.pub  known_hosts

参数说明：
参数说明：
-t 指定要创建的密钥类型
dsa | ecdsa | ecdsa-sk | ed25519 | ed25519-sk | RSA
可能的值为“dsa”、“ecdsa”、“ecdsa-sk”、“ed25519”、“ed25519-sk”或“rsa”。
当使用 RSA CA 密钥签署证书时，此标志还可用于指定所需的签名类型。可用的 RSA 签名变体是“ssh-rsa”（SHA1 签名，不推荐）、“rsa-sha2-256”和“rsa-sha2-512”（默认值）

-P 密码
提供（旧）密码。
这里的密码，是密钥的密码，不是远程主机的密码，随便设置。但是，这就失去了免密登陆的意义。因为，设置了这个后，登陆远程主机时，就必须输入密钥密码。
所以，一般这个指指定为空即可。

-f 文件名
指定密钥文件的文件名
这里的文件名，必须指定为 id_rsa ，不然，把密钥推送到目标机器，依然无法实现免密登陆。

总结：
就三个命令

cd                            进入当前账号家目录
ssh-keygen                    连续三次回车        
ssh-copy-id 192.168.31.15    复制公钥到hadoop104服务器，这样，就可以免密访问hadoop104服务器

这里用户账号省略，则使用当前账号进行免密登陆
比如，当前账号是 test

ssh-copy-id 192.168.31.15 等价与 ssh-copy-id test@192.168.31.15

实现的效果是，当前服务器的 test 账号可以免密登陆 15 服务器的 test 账号
参考资料：https://www.cnblogs.com/dirigent/p/16636545.html