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【Telnet】Telnet安装与配置

一、参考链接

telnet-server-0.17-66.el7.x86_64.rpm

telnet-0.17-66.el7.x86_64.rpm

二、Telnet介绍

Telnet是一种应用层协议，使用于互联网及局域网中，使用虚拟终端的形式，提供双向、以文字字符串为主的命令行接口交互功能。属于TCP/IP协议族的其中之一，是互联网远程登录服务的标准协议和主要方式，常用于服务器的远程控制，可供用户在本地主机执行远程主机上的工作。

三、Telnet安装与配置

本实验基于CentOS 7.9 系统进行操作演示。

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

1 、查询telnet相关服务组件是否已安装

查询telnet-server、telnet-client、xinetd等服务组件是否安装。

查询得知，xinetd、telnet和telnet-server未安装。

[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 系统的超级守护进程，长期驻存于后台，并监听来自网络的请求，从而启动对应的服务。而 telnet 正是 xinetd 管辖的服务之一。

2、查询YUM源中是否提供telnet相关组件

查看一下所配置的YUM源内是否提供了telnet相关的安装包

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、安装telnet相关服务组件

包含telnet、telnet-server、xinetd服务组件

yum install -y xinetd telnet telnet-server

# 执行此命令进行安装
yum install -y xinetd telnet telnet-server

4、查询是否安装完成

yum list | grep telnet && yum list | grep xinetd

# 执行此命令查询，带@符号的表示已安装。
[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

# 参考链接：https://www.cnblogs.com/gengbo/p/15913541.html
# 查询所有已安装的软件信息
[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

# 显示详细信息
[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://bugs.centos.org>
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


# 显示所有文件列表
[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、启动telnet相关服务

执行命令，开启服务，并设置开机自启动。

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

6、查看服务监听端口

[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 ~]#

四、Telnet远程连接测试

1、创建用户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用户telnet登录

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、设置允许ROOT用户Telnet登录

参考链接：[telnet允许root用户登录 - 规格严格-功夫到家 - 博客园](https://www.cnblogs.com/diyunpeng/p/8403534.html#:~:text=telnet允许root用户登录默认情况下，linux不允许root用户以telnet方式登录linux主机，若要允许root用户登录，可采取以下3种方法之一： 1、修改login文件 redhat中对于远程登录的限制体现在,%2Fetc%2Fpam.d%2Flogin 文件中，如果把限制的内容注销掉，那么限制将不起作用。)

1️⃣# 修改login文件
 vim /etc/pam.d/login
 注释这一行文件
 #account    required     pam_nologin.so
按:wq保存退出。

2️⃣# 注释掉securetty文件
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 ~]#