Linux学习笔记（7）

###1.openssh-server####


功能：让远程主机可以通过网络访问sshd服务，开启一个安全shell


####2.客户端连接方式####
ssh 远程主机用户@远程主机ip
[root@server2 ~]# ssh root@172.25.34.1
The authenticity of host '172.25.34.1 (172.25.34.1)' 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 '172.25.34.1' (ECDSA) to the list of known hosts.
root@172.25.34.1's password: ##远程用户密码
Last login: Sun   Jul 30 03:13:47 2017
[root@server1 ~]# ##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ip command##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@server1 ~]# 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 [e-mail]
The key's randomart image is:
+--[ RSA 2048]----+
|o                |
|E.               |
|..               |
|.  . o           |
|.o. * . S        |
|oo.o o   .       |
|+ =. .  .        |
|o. oo.+..        |
|    ..o*.        |
+-----------------+
[root@server1 ~]# 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@server1 ~]# ssh-copy-id -i /root/.ssh/id_rsa.pub  root@172.25.34.1
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
172.25.34.1 ##被加密主机ip


3.分发钥匙给client主机
[root@server1 ~]# scp /root/.ssh/id_rsa root@172.25.34.2:/root/.ssh/


4.测试


[root@server2 ~]# ssh root@172.25.34.1 ##通过id_rsa直接连接不需要输入用户密码
Last login: Sun  Jul 30 03:20:47 2017 from 172.25.34.2
[root@server0 ~]# 


####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
sshd:all


50 DenyUsers westos ##用户黑名单
sshd:用户IP

黑名单先生效，白名单后生效。

在上面配置文件添加的黑白名单是针对本机用户

下面文件单独写的是对外来的sshd客户端的限制

2.控制ssh客户端访问
vim /etc/hosts.deny
sshd:ALL ##拒绝所有人链接sshd服务


vim /etc/hosts.allow
sshd:172.25.34.3 ##允许server3主机链接sshd


sshd:172.25.34.2， 172.25.34.3 ##允许250和180链接


sshd:ALL EXCEPT 172.25.254.3 ##只不允许200链接sshd




3.ssh登陆提示修改该

vim /etc/motd ##显示登陆后字符

hello world ##在登陆后就会显示这个字符