ssky-keygen + ssh-copy-id 无密码登陆远程LINUX主机

使用下例中ssky-keygen和ssh-copy-id，仅需通过3个步骤的简单设置而无需输入密码就能登录远程Linux主机。 
ssh-keygen 创建公钥和密钥。 
ssh-copy-id 把本地主机的公钥复制到远程主机的authorized_keys文件上。
ssh-copy-id 也会给远程主机的用户主目录（home）和~/.ssh, 和~/.ssh/authorized_keys设置合适的权限 。

步骤1: 用 ssh-key-gen 在本地主机上创建公钥和密钥

root@zc-Lenovo-B450:~$  ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/zc/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/zc/.ssh/id_rsa.
Your public key has been saved in /home/zc/.ssh/id_rsa.pub.
The key fingerprint is:
db:fd:13:dc:f5:99:4b:0a:c1:53:bf:f3:5f:c3:5c:2e zc@zc-Lenovo-B450
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|             .   |
|          . . .  |
|           +   ..|
|        S   o. .B|
|         o o  =B+|
|        . . o E=*|
|             o.o+|
|              ..o|
+-----------------+

步骤2: 用 ssh-copy-id 把公钥复制到远程主机上

root@zc-Lenovo-B450:~$ ssh-copy-id 192.168.0.191
root@192.168.0.191's password: 
Now try logging into the machine, with "ssh '192.168.0.191'", and check in:

  ~/.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

步骤3: 直接登录远程主机

root@zc-Lenovo-B450:/home/zc# ssh 192.168.0.191
Welcome to Ubuntu 11.10 (GNU/Linux 3.0.0-17-generic-pae i686)

 * Documentation:  https://help.ubuntu.com/

364 packages can be updated.
299 updates are security updates.

New release '12.04 LTS' available.
Run 'do-release-upgrade' to upgrade to it.

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Last login: Mon Feb  4 15:02:51 2013 from zc-lenovo-b450.local