1、在主机A生成秘钥对
  1. ssh-keygen -t rsa
  4. ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa

一路回车，最后会生成秘钥对：
Your identification has been saved in /home/test/.ssh/id_rsa.
Your public key has been saved in /home/test/.ssh/id_rsa.pub.

2、将公钥复制到主机B
  1. ssh-copy-id -p 22 -i ~/.ssh/id_rsa.pub test@192.168.11.2
  2. # 然后会让输入密码

这时候登录主机B，会发现在/home/test/.ssh/目录下多个文件authorized_keys。这个时候A已经可以免密登录到B了
这一步也可以使用scp命令将id_rsa.pub拷贝过来，然后将id_rsa.pub的内容吧追加到/home/test/.ssh/authorized_keys

  1. cat id_rsa.pub >> /home/test/.ssh/authorized_keys 
  2. • 1

这个是单向的，B要免密登录到A的话反向操作一遍就可以了。