什么是ssh

管理员可以通过远程登陆的方式，对通过网相连的分散于各处的多台主机进行管理操作。

管理员可以对远程主机进行如下操作：

遗憾的事情是：这些操作不安全！

使用纯文本口令，并用明文发送

在日常操作练习时，用ssh登录其他主机时，可能会每次都需要输入登录密码，哪怕用scp复制东西也需要。

为了更方便快捷的切换主机，ssh免密通信不失为更好的选择；

用ssh-keygen生成密钥，默认保存在本地的/root/.ssh/id_rsa

然后在用ssh-copy-id分发至目标主机之上；登录用户@主机名或IP地址

注意：

    1.最好是用主机名，重庆电脑外包公司，在/etc/hosts文件中写入主机名和对应的IP地址；

    2.免密通信需要双方相互认证，所以也需要在目标主机对本机做一次相同的操作；

[root@www ~]# ssh-keygen -t rsa -P '' 
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): 
/root/.ssh/id_rsa already exists.
Overwrite (y/n)?

[root@www ~]#ssh-copy-id -i .ssh/id_rsa.pub root@172.16.75.1
/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: ".ssh/id_rsa.pub"
The authenticity of host '172.16.75.1 (172.16.75.1)' can't be established.
ECDSA key fingerprint is SHA256:YXhbTS9MfK2IQC4gtOW4RL8voHvFqC1cAAMJXuF3Wec.
ECDSA key fingerprint is MD5:2c:c0:94:e8:3a:e4:74:88:c0:d8:e0:01:20:81:1d:8e.
Are you sure you want to continue connecting (yes/no)? yes
/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@172.16.75.1's password: 
Number of key(s) added: 1
Now try logging into the machine, with:  "ssh 'root@172.16.75.1'"
and check to make sure that only the key(s) you wanted were added.