centos7 配置ssh 免密码登陆

我只有一台机器，是因为要配置hadoop分布式环境用，需要配置ssh

两个用户:　　zhangxs,　　root

首先在切换到zhangxs用户下

执行【 ssh-keygen -t rsa】

[zhangxs@zhangxs Desktop]$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/zhangxs/.ssh/id_rsa):
Created directory '/home/zhangxs/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/zhangxs/.ssh/id_rsa.
Your public key has been saved in /home/zhangxs/.ssh/id_rsa.pub.
The key fingerprint is:
0f:4b:e9:0f:::a5::ea:2e:9b::3a:0e::4d zhangxs@zhangxs
The key's randomart image is:
+--[ RSA ]----+
|        . .      |
|       o o       |
|      o o        |
|       + .       |
|    E   S        |
|   o   + =       |
|  + . o * .      |
| o .. .B o       |
|   .oo+.  .      |
+-----------------+
默认会在当前用户的home/$用户名 目录下生成一个.ssh文件夹，这个是隐藏文件夹
 cd /home/zhangxs/  切换到文件夹下，输入 [ll -a]
[zhangxs@zhangxs ~]$ ll -a
total 36
drwx------. 22 zhangxs zhangxs 4096 3月  19 14:48 .
drwxr-xr-x.  3 root    root      21 3月  18 17:50 ..
drwx------.  3 zhangxs zhangxs   26 3月  18 23:06 .adobe
-rw-------.  1 zhangxs zhangxs  470 3月  19 14:50 .bash_history
-rw-r--r--.  1 zhangxs zhangxs   18 8月   3 2016 .bash_logout
-rw-r--r--.  1 zhangxs zhangxs  193 8月   3 2016 .bash_profile
-rw-r--r--.  1 zhangxs zhangxs  231 8月   3 2016 .bashrc
drwx------. 17 zhangxs zhangxs 4096 3月  18 20:59 .cache
drwxr-xr-x. 19 zhangxs zhangxs 4096 3月  18 20:08 .config
drwxr-xr-x.  4 root    root      48 3月  19 01:00 datainfo
drwxr-xr-x.  2 zhangxs zhangxs  220 3月  19 14:22 Desktop
drwxr-xr-x.  2 zhangxs zhangxs    6 3月  18 18:00 Documents
drwxr-xr-x.  2 zhangxs zhangxs   51 3月  19 00:00 Downloads
-rw-------.  1 zhangxs zhangxs   16 3月  18 18:00 .esd_auth
-rw-------.  1 zhangxs zhangxs 1554 3月  19 14:12 .ICEauthority
drwxrwxr-x.  3 zhangxs zhangxs   19 3月  18 18:24 .java
drwx------.  3 zhangxs zhangxs   19 3月  18 18:00 .local
drwx------.  3 zhangxs zhangxs   26 3月  18 23:06 .macromedia
drwxr-xr-x.  5 zhangxs zhangxs   54 3月  18 18:04 .mozilla
drwxr-xr-x.  2 zhangxs zhangxs    6 3月  18 18:00 Music
drwxr-xr-x.  4 zhangxs zhangxs   89 3月  18 23:21 Pictures
drwxrw----.  3 zhangxs zhangxs   19 3月  19 01:08 .pki
drwxr-xr-x.  2 zhangxs zhangxs    6 3月  18 18:00 Public
drwxr-xr-x.  3 zhangxs zhangxs   17 3月  18 18:00 .redhat
drwx------.  4 zhangxs zhangxs   48 3月  18 18:26 .speech-dispatcher
drwx------.  2 zhangxs zhangxs   80 3月  19 14:49 .ssh
drwxr-xr-x.  2 zhangxs zhangxs    6 3月  18 18:00 Templates
drwxr-xr-x.  2 zhangxs zhangxs    6 3月  18 18:00 Videos

【cd .ssh】 文件下，有两个文件

-rw-------.  zhangxs zhangxs  3月   : id_rsa
-rw-r--r--.  zhangxs zhangxs   3月   : id_rsa.pub

【cp id_rsa.pub authorized_keys】  复制文件

【ssh localhost】 以ssh方式登陆localhost，执行完后会在当前目录下生成两个文件

[zhangxs@zhangxs .ssh]$ ssh localhost
The authenticity of host 'localhost (127.0.0.1)' can't be established.
ECDSA key fingerprint is ::8a::0b:f3:5d:7f:::1b:db::3e:b4:.
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.
Last login: Sun Mar  :: 

--------------------------------------------------------------------------------------------

因为是要配置为分布式，所以要root用户到zhangxs用户，

首先要看在在hosts中是否配置好

[zhangxs@zhangxs .ssh]$ more /etc/hosts
127.0.0.1   localhost
192.168.177.120 hadoop-zhangxs.com zhangxs

网卡中是否配置好(如果网卡中没有配置，在ssh zhangxs 时会报错：([root@zhangxs .ssh]# ssh zhangxs
ssh: connect to host zhangxs port 22: Connection timed out)

[root@zhangxs sbin]# ifconfig
enp1s0f0: flags=<UP,BROADCAST,MULTICAST>  mtu
        inet 192.168.177.120  netmask 255.255.255.0  broadcast 192.168.177.255
        ether f8:a9::::7e  txqueuelen   (Ethernet)
        RX packets   bytes  (0.0 B)
        RX errors   dropped   overruns   frame
        TX packets   bytes  (0.0 B)
        TX errors   dropped  overruns   carrier   collisions
        device interrupt   

这两个都没问题就可以，切换到root用户    执行【 ssh-keygen -t rsa】
后面步骤都一样拉！！！！！！！！！