$ ssh-keygen 
Generating public/private rsa key pair. 
Enter file in which to save the key (/root/.ssh/id_rsa):    #密钥文件存放路径，默认是执行命令的用户的家目录
Created directory '/root/.ssh'.                           #在用户的根目录生成一个 .ssh 的目录
Enter passphrase (empty for no passphrase):                  #输入密码短语（空表示没有密码短语）
Enter same passphrase again:                                #再次输入密码短语
Your identification has been saved in /root/.ssh/id_rsa.     #生成的私钥文件
Your public key has been saved in /root/.ssh/id_rsa.pub.     #生成的公钥文件
The key fingerprint is:
SHA256:BkB4+5l17YJpYw22sJjpGg0GJxi1s8DCt0WNSsLpBM4 root@localhost.localdomain
The key's randomart image is:
+---[RSA 2048]----+
|=.ooo.o          |
|**.ooo .         |
|OE*o.o.    .     |
|.*.++ ..+ . .    |
|  +. = BSB .     |
| . o+ =.B o .    |
|  ...  o . .     |
|   ..            |
|  ..             |
+----[SHA256]-----+

$ ls -la
total 16
-rw-rw-r--. 1 root root  395 Nov 30 23:04 authorized_keys
-rw-------. 1 root root 1675 Nov 30 23:04 id_rsa
-rw-r--r--. 1 root root  395 Nov 30 23:04 id_rsa.pub
-rw-r--r--. 1 root root  516 Nov 30 23:33 known_hosts
# authorized_keys 存放其他实例远程免密登录的公钥，默认没有。主要是存放多台实例的公钥
# id_rsa 生成的私钥文件
# id_rsa.pub 生成的公钥文件
# known_hosts 已知的实例，(连接实例的时候需要你选择 yes/no 的时候，选 yes 就会存在这个文件里)

$ ssh-copy-id -i ~/.ssh/id_rsa.pub 10.10.12.7
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/jarbo/.ssh/id_rsa.pub"
The authenticity of host '10.10.12.7 (10.10.12.7)' can't be established.
ECDSA key fingerprint is SHA256:fx6FzTUrpVop0TbFhIAj2tvsLMaQd/4ykQ5nHFFxtU4.
ECDSA key fingerprint is MD5:84:5e:2f:b8:01:09:7e:df:76:cc:a8:3c:5c:c3:c0:e0.
Are you sure you want to continue connecting (yes/no)? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
jarbo@10.10.12.7's password: 

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh '10.10.12.7'"
and check to make sure that only the key(s) you wanted were added.
# ssh-copy-id 命令会把本地当前用户的公钥复制发送到远端实例上，并自动创建 `authorized_keys` 文件和 `.ssh` 目录，并设置合适的权限。`authorized_keys` 文件需要 `600` 权限，`.ssh` 目录需要 `700` 权限。

$ mkdir ~/.ssh/
#远程实例

$ cd ~/.ssh/
$ cat id_rsa.pub >> authorized_keys
$ scp ~/.ssh/authorized_keys user@romte ip
#本地实例,不加 user 默认使用本地执行 scp 命令的用户

$ chmod 700 ~/.ssh/
$ chmod 600 ~/.ssh/authorized_keys
# .ssh 目录的权限必须是 700
# authorized_keys 文件权限必须是 600