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@desktop0 ~]# ssh root@x.x.x.x
The authenticity of host 'x.x.x.x' 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 '172.25.0.11' (ECDSA) to the list of known hosts.
root@x.x.x.x's password: ##远程用户密码
Last login: Mon Oct time
[root@server0 ~]###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
3.sshkey加密
1.生成公钥私钥
[root@server0 ~]# ssh-keygen ##生成公钥私钥工具
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）
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase): [enter]##密钥密码，必须>4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:
ab:3c:73:2e:c8:0b:75:c8:39:3a:46:a2:22:34:84:81 root@server0.example.com
The key's randomart p_w_picpath is:
+--[ RSA 2048]----+
|o |
|E. |
|.. |
|. . o |
|.o. * . S |
|oo.o o . |
|+ =. . . |
|o. oo.+.. |
| ..o*. |
+-----------------+
[root@server0 ~]# 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认证方式
[root@server0 ~]# ssh-copy-id -i /root/.ssh/id_rsa.pub root@x.x.x.x
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
x.x.x.x##被加密主机ip
3.分发钥匙给client主机
[root@server0 ~]# scp /root/.ssh/id_rsa root@x.x.x.x:/root/.ssh/
4.测试
[root@desktop0 ~]# ssh root@x.x.x.x##通过id_rsa直接连接不需要输入用户密码
Last login: Mon Oct 3 03:58:10 2016 from x.x.x.x
[root@server0 ~]#
####4.提升openssh的安全级别####
1.openssh-server配置文件
/etc/ssh/sshd_config
49 PermitRootLogin yes|no##是否允许超级用户登陆
79 PasswordAuthentication yes|no##是否开启用户密码认证，yes为支持no为关闭
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
DenyUsers westos##用户黑名单
