实现功能
主机A 免密访问 主机B。
创建秘钥
登录主机A，创建主机秘钥和公钥。
user@A:~$ ssh-keygen -t rsa
直接回车，使用默认值即可，秘钥文件默认生成到$HOME/.ssd/目录：
Generating public/private rsa key pair.
Enter file in which to save the key (/home/seewin/.ssh/id_rsa):
Created directory '/home/seewin/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/seewin/.ssh/id_rsa.
Your public key has been saved in /home/seewin/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:ut6DNj0a3jjrEAJRi4CsxXDfvnM83BV/BPODil3iuzY seewin@seewin
The key's randomart image is:
+---[RSA 2048]----+
|*+o o |
|o=oo . .+ |
|+.. . . ..o .o|
|.. . + +o ..|
| . . . S. +. . .|
| . . = . .. . |
| . =o= .. |
| o=O+. E. |
| +O=oo... |
+----[SHA256]-----+
复制公钥内容
user@A:~$ ssh-copy-id user@B
接下来，就可以在主机A上直接使用SSH或者SCP访问主机B了：
user@A:~$ ssh user@B
Welcome to Ubuntu 18.04.3 LTS (GNU/Linux 4.15.0-70-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
System information as of Sun Nov 24 00:51:15 UTC 2019
System load: 0.08 Processes: 106
Usage of /home: 0.0% of 858.31GB Users logged in: 1
Memory usage: 5% IP address for enp2s0: 192.168.1.2
Swap usage: 0%
0 packages can be updated.
0 updates are security updates.
Failed to connect to https://changelogs.ubuntu.com/meta-release-lts. Check your Internet connection or proxy settings
Last login: Sun Nov 24 00:46:36 2019 from 192.168.1.3
user@B:~$
或者，使用手工的方式将A的公钥拷贝到B主机：
user@A:~$ cat .ssh/id_rsa.pub
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQD4LnrbrQrUR58hvDZChgLnOQh1OobKmYWAr8QBtuV8FYS2NWBkf+UqKt9e8/xA6F32SUBOFGtSQcPCyr0eb6QyS6N0JSwWgvGVEe13HqgpDBucqdoRrsnap6zvvqANMN+dVg0wJ/WP07JyTgYXCoQmAFc5Xj1YtlaYLflWCXuqs5Dzr4jjqBQUNggAP3DASxF8RcDvhExUwGBxaymwh61TrucdcwE/NUlm2d52oXKnj89F1NduXpQzDoLyyAD7FVADcPTxcKuJwdyorBKrYsK1SMUyon3p6xD4SM7VGLNF9FQ+qYkxWLnUS3p0px6uP4LShHDGXFoJba0ab3NI6kCF user@A
创建默认认证
登录主机B，进入HOME/.ssh/目录。若没有.ssh目录，则创建该目录：
user@B:~$ mkdir ~/.ssh
检查是否存在authorized_keys文件，若不存在，则创建。
user@B:~$ touch authorized_keys
将主机A的公钥内容添加到authorized_keys文件末尾：
user@B:~$ vi authorized_keys
# 这里是原有内容，其它主机的公钥数据。
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQD4LnrbrQrUR58hvDZChgLnOQh1OobKmYWAr8QBtuV8FYS2NWBkf+UqKt9e8/xA6F32SUBOFGtSQcPCyr0eb6QyS6N0JSwWgvGVEe13HqgpDBucqdoRrsnap6zvvqANMN+dVg0wJ/WP07JyTgYXCoQmAFc5Xj1YtlaYLflWCXuqs5Dzr4jjqBQUNggAP3DASxF8RcDvhExUwGBxaymwh61TrucdcwE/NUlm2d52oXKnj89F1NduXpQzDoLyyAD7FVADcPTxcKuJwdyorBKrYsK1SMUyon3p6xD4SM7VGLNF9FQ+qYkxWLnUS3p0px6uP4LShHDGXFoJba0ab3NI6kCF user@A
验证免密登录
登录主机A，执行ssh 或 scp：
user@A:~$ ssh user@B
user@A:~$ scp abc.txt user@B:~/data/
