Centos7下实现免密码登录

一、生成密钥

[root@master ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
SHA256:pvR6iWfppGPSFZlAqP35/6DEtGTvaMY64otThWoBTuk root@localhost.localdomain
The key's randomart image is:
+---[RSA 2048]----+
|  .  o.          |
|.o  . .          |
|+. o . . o       |
| Eo o . +        |
|   o o..S.       |
|  o ..oO.o       |
| . . ..=*oo      |
|  ..o *=@+ .     |
|  .oo=+@+.o..    |
+----[SHA256]-----+

生成之后会在用户的根目录生成一个 “.ssh”的文件夹，进入“.ssh”会生成以下几个文件

authorized_keys id_rsa id_rsa.pub known_hosts

authorized_keys:存放远程免密登录的公钥,主要通过这个文件记录多台机器的公钥
id_rsa : 生成的私钥文件
id_rsa.pub ： 生成的公钥文件
know_hosts : 已知的主机公钥清单
如果希望ssh公钥生效需满足至少下面两个条件：
1) .ssh目录的权限必须是700
2) .ssh/authorized_keys文件权限必须是600

二、远程免密登录
1.原理：
- 客户端向服务器端发出连接请求
- 服务器端向客户端发出自己的公钥
- 客户端使用服务器端的公钥加密通讯密钥然后发给服务器端
- 如果通讯过程被截获，由于窃听者即使获知公钥和经过公钥加密的内容，但不拥有私 钥依然无法解密（RSA算法）
- 服务器端接收到密文后，用私钥解密，获知通讯密钥
2.常用以下几种方法：
2.1通过ssh-copy-id的方式 

[root@master ~]# ssh-copy-id -i root@slave1
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
root@worker1's password:

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'root@worker1'"
and check to make sure that only the key(s) you wanted were added.

2.2通过scp将内容写到对方的文件中

[root@test .ssh]# scp -p ~/.ssh/id_rsa.pub root@192.168.80.11:/root/.ssh/authorized_keys
root@192.168.80.11's password: 
id_rsa.pub 100% 408 0.4KB/s 00:00 
[root@test .ssh]# 
[root@test .ssh]# 
[root@test .ssh]# 
[root@test .ssh]# ssh root@192.168.80.11
Last login: Mon Oct 10 01:27:02 2016 from 192.168.80.10
[root@localhost ~]#

或者

scp ~/.ssh/id_rsa.pub root@<remote_ip>:pub_key //将文件拷贝至远程服务器
$ cat ~/pub_key >>~/.ssh/authorized_keys //将内容追加到authorized_keys文件中， 不过要登录远程服务器来执行这条命令