# Telnet安裝與配置

**本實驗基於我在cnaaa.com購買的雲伺服器CentOS 7.9 系統進行操作演示。**

```
[root@master ~]# cat /etc/redhat-release 
CentOS Linux release 7.9.2009 (Core)
```

### 1 、查詢telnet相關服務元件是否已安裝

> 查詢telnet-server、telnet-client、xinetd等服務元件是否安裝。
>
> **查詢得知，xinetd、telnet和telnet-server未安裝。**

```
[root@master ~]# rpm -qa | grep telnet
[root@master ~]# rpm -qa | grep xinetd
[root@master ~]# yum list | grep telnet
telnet.x86_64                1:0.17-66.el7              updates  
telnet-server.x86_64         1:0.17-66.el7              updates  
[root@master ~]# yum list | grep xinetd
xinetd.x86_64                               2:2.3.15-14.el7            base   
```

> **xinetd 是 Linux 系統的超級守護程式，長期駐存於後臺，並監聽來自網路的請求，從而啟動對應的服務。而 telnet 正是 xinetd 管轄的服務之一。**

### 2、查詢YUM源中是否提供telnet相關元件

> 檢視一下所配置的YUM源內是否提供了telnet相關的安裝包
>
> **yum provides telnet telnet-server xinetd**

```
[root@master ~]# yum list | grep telnet && yum list | grep xinetd
telnet.x86_64               1:0.17-66.el7              updates  
telnet-server.x86_64        1:0.17-66.el7              updates  
xinetd.x86_64               2:2.3.15-14.el7            base     
[root@master ~]# 
```

### 3、安裝telnet相關服務元件

> 包含telnet、telnet-server、xinetd服務元件
>
> **yum install -y xinetd telnet telnet-server**

```
# 執行此命令進行安裝
yum install -y xinetd telnet telnet-server
```

### 4、查詢是否安裝完成

> **yum list | grep telnet && yum list | grep xinetd**

```
# 執行此命令查詢，帶@符號的表示已安裝。
[root@master ~]# yum list | grep telnet && yum list | grep xinetd
telnet.x86_64             1:0.17-66.el7              @updates 
telnet-server.x86_64      1:0.17-66.el7              @updates 
xinetd.x86_64             2:2.3.15-14.el7            @base    
# 參考連結：https://www.cnblogs.com/gengbo/p/15913541.html
# 查詢所有已安裝的軟體資訊
[root@master ~]# rpm -qa telnet telnet-server xinetd
xinetd-2.3.15-14.el7.x86_64
telnet-server-0.17-66.el7.x86_64
telnet-0.17-66.el7.x86_64

# 顯示詳細資訊
[root@master ~]# rpm -qi telnet-server
Name        : telnet-server
Epoch       : 1
Version     : 0.17
Release     : 66.el7
Architecture: x86_64
Install Date: Tue 22 Feb 2022 11:34:33 AM CST
Group       : System Environment/Daemons
Size        : 56361
License     : BSD
Signature   : RSA/SHA256, Wed 18 Nov 2020 10:20:43 PM CST, Key ID 24c6a8a7f4a80eb5
Source RPM  : telnet-0.17-66.el7.src.rpm
Build Date  : Tue 17 Nov 2020 12:44:28 AM CST
Build Host  : x86-01.bsys.centos.org
Relocations : (not relocatable)
Packager    : CentOS BuildSystem <http:>
Vendor      : CentOS
URL         : http://web.archive.org/web/20070819111735/www.hcs.harvard.edu/~dholland/computers/old-netkit.html
Summary     : The server program for the Telnet remote login protocol
Description :
Telnet is a popular protocol for logging into remote systems over the
Internet. The package includes a daemon that supports Telnet remote
logins into the host machine. The daemon is disabled by default.
You may enable the daemon by editing /etc/xinetd.d/telnet

# 顯示所有檔案列表
[root@master ~]# rpm -ql telnet telnet-server xinetd
/usr/bin/telnet
/usr/share/doc/telnet-0.17
/usr/share/doc/telnet-0.17/README
/usr/share/man/man1/telnet.1.gz
/usr/lib/systemd/system/telnet.socket
/usr/lib/systemd/system/telnet@.service
/usr/sbin/in.telnetd
/usr/share/man/man5/issue.net.5.gz
/usr/share/man/man8/in.telnetd.8.gz
/usr/share/man/man8/telnetd.8.gz
/etc/sysconfig/xinetd
/etc/xinetd.conf
/etc/xinetd.d/chargen-dgram
/etc/xinetd.d/chargen-stream
/etc/xinetd.d/daytime-dgram
/etc/xinetd.d/daytime-stream
/etc/xinetd.d/discard-dgram
/etc/xinetd.d/discard-stream
/etc/xinetd.d/echo-dgram
/etc/xinetd.d/echo-stream
/etc/xinetd.d/tcpmux-server
/etc/xinetd.d/time-dgram
/etc/xinetd.d/time-stream
/usr/lib/systemd/system/xinetd.service
/usr/sbin/xinetd
/usr/share/doc/xinetd-2.3.15
/usr/share/doc/xinetd-2.3.15/CHANGELOG
/usr/share/doc/xinetd-2.3.15/COPYRIGHT
/usr/share/doc/xinetd-2.3.15/README
/usr/share/doc/xinetd-2.3.15/empty.conf
/usr/share/doc/xinetd-2.3.15/sample.conf
/usr/share/man/man5/xinetd.conf.5.gz
/usr/share/man/man5/xinetd.log.5.gz
/usr/share/man/man8/xinetd.8.gz
```

### 5、啟動telnet相關服務

> **執行命令，開啟服務，並設定開機自啟動。**

```
systemctl start telnet.socket xinetd
systemctl enable telnet.socket xinetd
systemctl status telnet.socket xinetd
```

### 6、檢視服務監聽埠

```
[root@master ~]# netstat -tnl |grep 23 
tcp6       0      0 :::23        :::*                    LISTEN     
[root@master ~]# ss -tunpl | grep 23
tcp    LISTEN     0      128    [::]:23   [::]:*          users:(("systemd",pid=1,fd=33))
[root@master ~]# 
```

## Telnet遠端連線測試

### 1、建立使用者xybdiy

```
[root@master ~]# useradd xybdiy
[root@master ~]# passwd xybdiy
Changing password for user xybdiy.
New password: 
BAD PASSWORD: The password is a palindrome
Retype new password: 
passwd: all authentication tokens updated successfully.
```

### 2、使用xybdiy使用者telnet登入

```
telnet 192.168.200.11

Kernel 3.10.0-1160.53.1.el7.x86_64 on an x86_64
master login: xybdiy
Password:
[xybdiy@master ~]$ su -
Password:
Last login: Tue Feb 22 12:39:35 CST 2022 on pts/1
Last failed login: Tue Feb 22 12:52:02 CST 2022 on pts/2
There was 1 failed login attempt since the last successful login.
[root@master ~]#
```

### 3、設定允許ROOT使用者Telnet登入

```
# 修改login檔案
 vim /etc/pam.d/login
 註釋這一行檔案
 #account    required     pam_nologin.so
按:wq儲存退出。

# 註釋掉securetty檔案
mv /etc/securetty /etc/securetty.bak
C:\Users\xybdiy>telnet 192.168.200.11

Kernel 3.10.0-1160.53.1.el7.x86_64 on an x86_64
master login: root
Password:
Last failed login: Tue Feb 22 13:59:24 CST 2022 from ::ffff:192.168.200.2 on pts/1
There was 1 failed login attempt since the last successful login.
Last login: Tue Feb 22 13:45:55 on pts/2
[root@master ~]#
[root@master ~]# telnet localhost
Trying ::1...
Connected to localhost.
Escape character is '^]'.

Kernel 3.10.0-1160.53.1.el7.x86_64 on an x86_64
master login: root
Password: 
Last login: Tue Feb 22 14:11:49 from ::ffff:192.168.200.2
[root@master ~]# 
```</http:>

Telnet安裝與配置

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