所谓公钥登录，就是用户将自己的公钥储存在远程主机上。登录的时候远程主机回向用户发送一段随机字符串，用户用自己的秘钥加密后再发送给远程主机。远程主机用事先储存的公钥进行解密，如果成功，就证明用户是可信的，直接允许登录shell，不再要求密码。
[Hadoop@hadoop01 ~]$ cd .ssh
[hadoop@hadoop01 .ssh]$ ls
authorized_keys id_rsa id_rsa.pub known_hosts
[hadoop@hadoop01 .ssh]$ rm -rf ./* #清空文件夹
[hadoop@hadoop01 .ssh]$ ssh-keygen -t rsa #生成公钥和秘钥
Generating public/private rsa key pair.
Enter file in which to save the key (/home/hadoop/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/hadoop/.ssh/id_rsa.
Your public key has been saved in /home/hadoop/.ssh/id_rsa.pub.
The key fingerprint is:
a2:78:65:72:49:9a:71:91:aa:8f:3b:3e:a8:b3:74:87 hadoop@hadoop01.zjl.com
The key's randomart image is:
+--[ RSA 2048]----+
| .. |
| .. |
| ..o |
| .* . |
| .+ * S |
| ...* . |
| o.Eo. |
|+ =.o |
|++o+ |
+-----------------+
[hadoop@hadoop01 .ssh]$ ll
total 8
-rw-------. 1 hadoop hadoop 1675 Jun 19 23:41 id_rsa #秘钥
-rw-r--r--. 1 hadoop hadoop 405 Jun 19 23:41 id_rsa.pub #公钥
[hadoop@hadoop01 .ssh]$ ssh-copy-id hadoop02.zjl.com #将公钥发送给远程主机
The authenticity of host 'hadoop01.zjl.com (192.168.0.131)' can't be established.
RSA key fingerprint is 60:10:35:2f:64:08:bf:82:e5:bc:56:8c:3d:60:18:13.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'hadoop01.zjl.com,192.168.0.131' (RSA) to the list of known hosts.
hadoop@hadoop01.zjl.com's password:
Now try logging into the machine, with "ssh 'hadoop01.zjl.com'", and check in:
.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.
[hadoop@hadoop01 .ssh]$ ssh hadoop01.zjl.com #无密码登录
Last login: Mon Jun 19 23:30:46 2017 from 192.168.0.1
[hadoop@hadoop02 ~]$ #无密码登录成功
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