环境：
系统版本：
[root@localhost ~]# cat /etc/redhat-release
CentOS Linux release 7.5.1804 (Core) //Centos 7.5系统
安装SSH：
[root@localhost ~]# rpm -qa | grep ssh //是否安装ssh
openssh-7.4p1-16.el7.x86_64
openssh-clients-7.4p1-16.el7.x86_64
openssh-server-7.4p1-16.el7.x86_64
libssh2-1.4.3-10.el7_2.1.x86_64
主机：
目标服务器：192.168.2.161
源服务器：192.168.2.195
配置免密：
1.在源服务器端生成密钥
[root@localhost ~]# ssh-keygen -t rsa //无需配置，一路回车
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
/root/.ssh/id_rsa already exists.
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:`[root@localhost ~]# ls ./.ssh/
authorized_keys id_rsa id_rsa.pub known_hosts`
SHA256:8vvhVMFr1nPngJkod+CoCBfDxD2aCcO1duiXW9dZE6Y root@localhost.localdomain
The key's randomart image is:
+---[RSA 2048]----+
| . oo. o |
| +o.oo . o . |
| oB+.. . E o |
| o++ . o + X . |
| . o + S = % + o|
| o o * + = =.|
| . o . o .|
| + . |
| ..o |
+----[SHA256]-----+
2.查看生成的公私钥
[root@localhost ~]# ls ./.ssh/
authorized_keys id_rsa id_rsa.pub known_hosts
- id_rsa 私钥
- id_rsa.pub 公钥
3.上传公钥至目标服务器端
[root@localhost ~]# ssh-copy-id -i ./.ssh/id_rsa.pub root@192.168.2.161
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "./.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@192.168.2.161's password:
Number of key(s) added: 1
Now try logging into the machine, with: "ssh 'root@192.168.2.161'"
and check to make sure that only the key(s) you wanted were added.
4.测试免密登录目标服务器端
[root@localhost ~]# ssh root@192.168.2.161 //成功免密登录
Last login: Tue Mar 24 17:03:27 2020 from 192.168.2.161
小结：
以上配置只是单向免密，如果需要配置目标服务器与源服务器之间互相免密登录，需要在目标服务器上做同样的操作，将公钥上传至源服务器端即可。
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