##################1.openssh-server
功能：让远程主机可以通过网络访问sshd服务，开始一个安全shell
##################2.客户端连接方式
ssh远程主机用户@远程主机ip
[root@server45 ~]# ssh root@172.25.254.177
The authenticity of host '172.25.254.177 (172.25.254.177)' can't be established.
ECDSA key fingerprint is eb:24:0e:07:96:26:b1:04:c2:37:0c:78:2d:bc:b0:08.
Are you sure you want to continue connecting (yes/no)? yes ##连接陌生主机时需要建立认证关系
Warning: Permanently added '172.25.254.177' (ECDSA) to the list of known hosts.
root@172.25.254.177's password: ##远程用户密码
Last login: Mon Oct 3 20:54:06 2016 from foundation45.ilt.example.com
[root@foundation177 ~]# ##登陆成功
ssh 远程主机用户@远程主机ip -X##调用远程主机图形工具
ssh 远程主机用户@远程主机ipcommand##直接在远程主机运行某条命
令
ssh root@172.25.254.177 -X “gedit& firefox&” 同时打开两个工具
##################3.sshkey加密
1)生成公钥私钥
[root@foundation177 ~]# ssh-keygen ##生成公钥私钥的工具
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): [enter] ##加密字符保存文件（建议用默认）
Enter passphrase (empty for no passphrase): [enter] ##密钥密钥，必须大于四个 字符
Enter same passphrase again: [enter] ##确认密码
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:
bb:9f:a7:cb:6b:4c:1d:ad:1c:84:72:30:b8:fb:91:ad root@foundation177.ilt.example.com
The key's randomart p_w_picpath is:
+--[ RSA 2048]----+
| .o. . |
| . ..o . |
| . o . . |
| . o . |
| .So o + |
| . o.o + |
| ..= |
| Eoo.. |
| .oB= |
+-----------------+
[root@foundation177 ~]#
[root@foundation177 ~]# ls /root/.ssh/
id_rsa id_rsa.pub
id_rsa##私钥，就是钥匙
id_rsa.pub##公钥，就是锁
2)添加key的认证方式
[root@foundation177 ~]# ssh-copy-id -i /root/.ssh/id_rsa.pub root@172.25.254.177
ssh-copy-id##添加key认证方式的工具
-i##指定加密key文件
/root/.ssh/id_rsa.pub##加密key
root##加密用户为root
172.25.254.177##被加密主机ip
3）.分发钥匙给client主机
[root@foundation177 ~]scp /root/.ssh/id_rsa root@172.25.254.150:/root/.ssh/
4）测试
[root@server45 ~]# ssh 172.25.254.177 ##通过id_rsa直接连接不需要输入用户密码
Last login: Mon Oct 3 20:57:31 2016 from foundation150.ilt.example.com
[root@foundation177 ~]#
###############4.提升openssh的安全级别
1.openssh-server配置文件
/etc/ssh/sshd_config
78 PasswordAuthentication yes|no##是否开启用户密码认证，yes为支持no为关闭
48 PermitRootLogin yes|no##是否允许超级用户登陆
49 AllowUsers student westos##用户白名单，只有在名单中出现的用户可以使用sshd建立shell
50 DenyUsers westos##用户黑名单