ssh-keygen ssh-copy-id 无密码登陆
进行android开发经常需要登录远程ubuntu server服务器进行编译查看代码等，每次都需要输入密码，很烦人。
使用 ssh-keygen和ssh-copy-id配置一下就可以无需输入密码直接登录服务器了。
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 。
user@machine:~$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/id_rsa.pub.
The key fingerprint is:
43:c6:7d:c4:9c:85:bd:8f:f0:5a:b7:8b:37:e6:e9:12 user@machine
The key's randomart image is:
+--[ RSA 2048]----+
| o.=. |
| . . .= . |
| + . . . |
| o .. . |
| S o o |
| . E+ o|
| o...|
| ...=.|
| .*=o|
+-----------------+
user@machine:~$
user@machine:~$ ls -l .ssh/
total 12
-rw------- 1 user user 1679 Sep 4 16:34 id_rsa
-rw-r--r-- 1 user user 393 Sep 4 16:34 id_rsa.pub
-rw-r--r-- 1 user user 222 Sep 3 13:03 known_hosts
user@machine:~$ ssh-copy-id -i .ssh/id_rsa.pub user@172.16.2.15
user@172.16.2.15's password:
Now try logging into the machine, with "ssh 'user@172.16.2.15'", and check in:
~/.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.
user@machine:~$ ssh user@172.16.2.15
如果有端口号的话：
ssh-copy-id -i ~/.ssh/id_rsa.pub -p 20022
