两台服务器 A B
目标：A服务器不输入密码，直接登录B服务器
制作密钥对
登录A，执行下面命令，创建密钥对
# ssh-keygen -t rsa
一路回车默认就行，也可以在其中输入密码时输入本机密码
[root@host ~]$ ssh-keygen -t rsa <== 建立密钥对
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): <== 按 Enter
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase): <== 输入密钥锁码，或直接按 Enter 留空
Enter same passphrase again: <== 再输入一遍密钥锁码
Your identification has been saved in /root/.ssh/id_rsa. <== 私钥
Your public key has been saved in /root/.ssh/id_rsa.pub. <== 公钥
The key fingerprint is:
...现在，在 root 用户的家目录中生成了一个 .ssh 的隐藏目录，内含两个密钥文件。
id_rsa 为私钥，
id_rsa.pub 为公钥。
B服务器装公钥
拷贝id_rsa.pub文件到B服务器
# scp .ssh/id_rsa.pub to B在/root/.ssh/文件下新建文件authorized_keys
# touce /root/.ssh/authorized_keys将公钥内容写入authorized_keys文件
# cat id_rsa.pub >> /root/.ssh/authorized_keys
给文件赋权限
# chmod 600 authorized_keys
此时就可以在A服务器上免密登录B服务器
