Linux ->> Ubuntu 14.04 LTE下配置SSH免密码登录

首先用apt-get命令安装SSH

jerry@ubuntu:~$ sudo apt-get install ssh
[sudo] password for jerry:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following extra packages will be installed:
  libck-connector0 ncurses-term openssh-server openssh-sftp-server
  ssh-import-id
Suggested packages:
  rssh molly-guard monkeysphere
The following NEW packages will be installed:
  libck-connector0 ncurses-term openssh-server openssh-sftp-server ssh
  ssh-import-id
 upgraded,  newly installed,  to remove and  not upgraded.
Need to get  kB of archives.
After this operation, , kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get: http://us.archive.ubuntu.com/ubuntu/ trusty/main libck-connector0 amd64 0.4.5-3.1ubuntu2 [10.5 kB]
Get: http://us.archive.ubuntu.com/ubuntu/ trusty/main ncurses-term all 5.9+20140118-1ubuntu1 [243 kB]
Get: http://us.archive.ubuntu.com/ubuntu/ trusty-updates/main openssh-sftp-server amd64 1:6.6p1-2ubuntu2.3 [34.1 kB]

查找下用户目录下有没有.ssh文件夹。这个文件夹本身是个隐藏文件夹。安装SSH的时候应该默认会在安装用户的个人目录下创建改文件，如果没有就自己手动创建一个。至于它是用来干嘛的？SSH使用的是公钥加密。这个文件夹就是用来存放公钥和私钥两个文件的文件夹。

jerry@ubuntu:~$ ls -a -d .ssh ~
ls: cannot access .ssh: No such file or directory
/home/jerry
jerry@ubuntu:~$ mkdir ~/.ssh
jerry@ubuntu:~$ ls -a -d .ssh ~
/home/jerry  .ssh
jerry@ubuntu:~$ 

接下来就是生成密钥了。这里用ssh_keygen命令生成密钥。-t表示加密类型，ssh支持rsa（目前流行的公钥加密算法）/dsa（digital signature algorithm数字签名算法）。-f表示公钥和私钥文件保存的路径。可以看到.ssh文件夹下生成了id_dsa（私钥）和id_dsa.pub（公钥）两个文件。

jerry@ubuntu:~$ ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa
Generating public/private dsa key pair.
Your identification has been saved in /home/jerry/.ssh/id_dsa.
Your public key has been saved in /home/jerry/.ssh/id_dsa.pub.
The key fingerprint is:
e8:::7d:ae:::::2f:::5d:b0:b3: jerry@ubuntu
The key's randomart image is:
+--[ DSA ]----+
|        o.o. ..  |
|       . o.  ..  |
|         E. . .o.|
|       .  =. + .+|
|      . S.. + o o|
|     .   . . . = |
|      . .     . o|
|       .       o |
|              .  |
+-----------------+

jerry@ubuntu:~$ ls -a ~/.ssh/
 . .. id_dsa id_dsa.pub
 jerry@ubuntu:~$

添加公钥到认证的公钥证书列表中

jerry@ubuntu:~$ cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys
jerry@ubuntu:~$ 

尝试用SSH连接本地服务器

jerry@ubuntu:~$ ssh localhost
The authenticity of host 'localhost (127.0.0.1)' can't be established.
ECDSA key fingerprint is da:b7:c3:2a:ea:a2::4c:c3:c1::ca:0e:c2:ea:.
Are you sure you want to continue connecting (yes/no)? y
Please type 'yes' or 'no': yes
Warning: Permanently added 'localhost' (ECDSA) to the list of known hosts.
Welcome to Ubuntu 14.04. LTS (GNU/Linux 3.19.--generic x86_64)

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

The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.

jerry@ubuntu:~$ 

有用的链接：

用ssh-keygen来设置ssh无密码登录

ssh: connect to host h2 port 22: No route to host

ssh登录　The authenticity of host 192.168.0.xxx can't be established.　的问题

SSH 登录失败：Host key verification failed 的处理方法