$ ssh-keygen

生成的私钥key默认保存在~/.ssh/id_rsa文件中。重复执行这个命令会覆盖这个文件，会导致之前的key无法使用。
生成过程中会提示加密，建议输入一个密码进行安全保护。

Output
Your identification has been saved in /your_home/.ssh/id_rsa.
Your public key has been saved in /your_home/.ssh/id_rsa.pub(公钥).
The key fingerprint is:
a9:49:2e:2a:5e:33:3e:a9:de:4e:77:11:58:b6:90:26 username@remote_host
The key's randomart image is:
+--[ RSA 2048]----+
|     ..o         |
|   E o= .        |
|    o. o         |
|        ..       |
|      ..S        |
|     o o.        |
|   =o.+.         |
|. =++..          |
|o=++.            |
+-----------------+

2.将公钥上传到服务器
方法一　使用ssh-copy-id　最简单

$ ssh-copy-id username@remote_host
Output
/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
username@203.0.113.1's password:

方法二　拷贝

cat ~/.ssh/id_rsa.pub | ssh username@remote_host "mkdir -p ~/.ssh && touch ~/.ssh/authorized_keys && chmod -R go= ~/.ssh && cat >> ~/.ssh/authorized_keys"

方法三　手动将id_rsq.pub的内容粘贴到服务器的~/.ssh/authorized_keys

id_rsa.pub file to the ~/.ssh/authorized_keys

3.登录远端服务器
$ ssh username@remote_host

4.禁用服务器的密码登录（可选）
sudo nano /etc/ssh/sshd_config
PasswordAuthentication no
sudo systemctl restart ssh