sshd使用

sshd服务

1.sshd介绍
     sshd为secure shell的简称；可以通过网络在主机中开机shell的服务

连接方式（在客户端）：ssh username@ip  #文本模式
                    ssh -X username@ip  #可以在链接成功后开启图形界面

注意：
    第一次链接陌生主机是要建立认证文件,然后会询问是否建立，需要输入yes
    再次链接此台主机时，因为已经生成~/.ssh/know_hosts文件所以不需要再次输入yes

远程复制：  格式 scp file root@id:dir(文件的上传)

scp root@if:/dir file(文件的下载)

• 示例：把177主机下/mnt/file1文件上传到 172.25.254.97主机的/root/Desktop/目录下：

[root@localhost mnt]# ls niu/
   file1  file2  file3  file4  file5
   [root@localhost mnt]# scp niu/file1 root@172.25.254.97:/root/Desktop/
   file1                                         100%    0     0.0KB/s   00:00

此时可以在97主机下的桌面上看到file1：

   [root@localhost ~]# cd /root/Desktop/
   [root@localhost Desktop]# ls
   file1

• 示例：把97主机桌面下的file文件下载到177主机的/mnt/目录下：

   [root@localhost ~]# scp root@172.25.254.97:/root/Desktop/file /mnt/
    file                                          100%    0     0.0KB/s   00:00

此时可以在177主机上/mnt/目录下可以看到file文件

   [root@localhost ~]# ls /mnt/
   file  niu  root@172.25.254.97

2.sshd 的key认证

【1】生成认证KEY

生成密钥的命令：ssh-keygen

[root@localhost ~]# rm -rf .ssh/
[root@localhost ~]# ls -a
.                .bash_logout   .config    Downloads      Music     Templates
..               .bash_profile  .cshrc     .esd_auth      Pictures  Videos
anaconda-ks.cfg  .bashrc        Desktop    .ICEauthority  Public    .viminfo
.bash_history    .cache         Documents  .local         .tcshrc
[root@localhost ~]# ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): 
Created directory '/root/.ssh'.
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:
8c:23:ee:39:11:6b:e6:af:a3:76:b1:00:a5:6e:d1:d3 root@localhost
The key's randomart image is:
+--[ RSA 2048]----+
|                 |
|  .              |
| o. .            |
|o. o.E o         |
|... ooo S        |
| o..*. .         |
|.  =.+           |
|  ..*.           |
| ..o+=.          |
+-----------------+

【2】加密服务

使用命令：ssh-copy-id -i /root/.ssh/id_rsa.pub  root@id

[root@localhost ~]# cd .ssh/
[root@localhost .ssh]# ls
id_rsa  id_rsa.pub

[root@localhost .ssh]# ssh-copy-id -i /root/.ssh/id_rsa.pub root@172.25.254.97
The authenticity of host '172.25.254.97 (172.25.254.97)' 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
/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@172.25.254.97's password: 
Number of key(s) added: 1
Now try logging into the machine, with:   "ssh 'root@172.25.254.97'"
and check to make sure that only the key(s) you wanted were added.

[root@localhost .ssh]# ls 
authorized_keys  id_rsa  id_rsa.pub  known_hosts

(此时authorized_keys文件，生成代表97主机加密成功;id-rsa为钥匙，id_rsa.pub为锁）

【3】分发钥匙

使用命令： scp /root/.ssh/id_rsa root@id:/root/.ssh/

[root@localhost .ssh]# ls 
authorized_keys  id_rsa  id_rsa.pub  known_hosts
[root@localhost .ssh]# scp id_rsa root@172.25.254.177:/root/.ssh/
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
Warning: Permanently added '172.25.254.177' (ECDSA) to the list of known hosts.
root@172.25.254.177's password: 
id_rsa                                        100% 1679     1.6KB/s   00:00 

**在177主机下进行验证：

[root@localhost ~]# ls .ssh/
id_rsa  known_hosts

【4】测试
在客户主机中（172.25.254.177）输入命令：ssh root@172.25.254.97

[root@localhost ~]# ssh root@172.25.254.97
Last login: Wed Jul 25 23:10:43 2018
此时不需要进行root用户的登陆，直接连接成功   

3.sshd的安全设定 
      PasswordAuthentication yes|no ##是否允许用户通过登陆系统的密码做sshd的认证，（在78行也可登录其他用户密码）
      PermitRootLogin yes|no ##是否允许root用户通过sshd服务的认证（48行）
      Allowusers student westos ##设定用户白名单，白名单出现默认不再名单中的用户不能使用sshd 
      Denyusers westos ##设定用户黑名单，黑名单出现默认不再名单中的用户可以使用sshd

注意：在服务端修改文件的配置：vim /etc/ssh/sshd_config 
           配置完成之后要重启服务：systemctl restart sshd.service

此文为装载