一、参考链接

阿里巴巴开源镜像站-OPSX镜像站-阿里云开发者社区

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

<font color=red>本实验基于CentOS 7.9 系统进行操作演示。</font>

  1. [root@master ~]# cat /etc/redhat-release 
  2. 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。

  1. [root@master ~]# rpm -qa | grep telnet
  2. [root@master ~]# rpm -qa | grep xinetd
  3. [root@master ~]# yum list | grep telnet
  4. telnet.x86_64                1:0.17-66.el7              updates  
  5. telnet-server.x86_64         1:0.17-66.el7              updates  
  6. [root@master ~]# yum list | grep xinetd
  7. 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

<font color=red>yum provides telnet telnet-server xinetd</font>

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

3、安装telnet相关服务组件

包含telnet、telnet-server、xinetd服务组件

<font color=red>yum install -y xinetd telnet telnet-server</font>

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

image-20220222113450796

4、查询是否安装完成

<font color=red>yum list | grep telnet && yum list | grep xinetd</font>

  1. # 执行此命令查询，带@符号的表示已安装。
  2. [root@master ~]# yum list | grep telnet && yum list | grep xinetd
  3. telnet.x86_64             1:0.17-66.el7              @updates 
  4. telnet-server.x86_64      1:0.17-66.el7              @updates 
  5. xinetd.x86_64             2:2.3.15-14.el7            @base
  1. # 参考链接：https://www.cnblogs.com/gengbo/p/15913541.html
  2. # 查询所有已安装的软件信息
  3. [root@master ~]# rpm -qa telnet telnet-server xinetd
  4. xinetd-2.3.15-14.el7.x86_64
  5. telnet-server-0.17-66.el7.x86_64
  6. telnet-0.17-66.el7.x86_64
  8. # 显示详细信息
  9. [root@master ~]# rpm -qi telnet-server
  10. Name        : telnet-server
  11. Epoch       : 1
  12. Version     : 0.17
  13. Release     : 66.el7
  14. Architecture: x86_64
  15. Install Date: Tue 22 Feb 2022 11:34:33 AM CST
  16. Group       : System Environment/Daemons
  17. Size        : 56361
  18. License     : BSD
  19. Signature   : RSA/SHA256, Wed 18 Nov 2020 10:20:43 PM CST, Key ID 24c6a8a7f4a80eb5
  20. Source RPM  : telnet-0.17-66.el7.src.rpm
  21. Build Date  : Tue 17 Nov 2020 12:44:28 AM CST
  22. Build Host  : x86-01.bsys.centos.org
  23. Relocations : (not relocatable)
  24. Packager    : CentOS BuildSystem <http://bugs.centos.org>
  25. Vendor      : CentOS
  26. URL         : http://web.archive.org/web/20070819111735/www.hcs.harvard.edu/~dholland/computers/old-netkit.html
  27. Summary     : The server program for the Telnet remote login protocol
  28. Description :
  29. Telnet is a popular protocol for logging into remote systems over the
  30. Internet. The package includes a daemon that supports Telnet remote
  31. logins into the host machine. The daemon is disabled by default.
  32. You may enable the daemon by editing /etc/xinetd.d/telnet
  35. # 显示所有文件列表
  36. [root@master ~]# rpm -ql telnet telnet-server xinetd
  37. /usr/bin/telnet
  38. /usr/share/doc/telnet-0.17
  39. /usr/share/doc/telnet-0.17/README
  40. /usr/share/man/man1/telnet.1.gz
  41. /usr/lib/systemd/system/telnet.socket
  42. /usr/lib/systemd/system/telnet@.service
  43. /usr/sbin/in.telnetd
  44. /usr/share/man/man5/issue.net.5.gz
  45. /usr/share/man/man8/in.telnetd.8.gz
  46. /usr/share/man/man8/telnetd.8.gz
  47. /etc/sysconfig/xinetd
  48. /etc/xinetd.conf
  49. /etc/xinetd.d/chargen-dgram
  50. /etc/xinetd.d/chargen-stream
  51. /etc/xinetd.d/daytime-dgram
  52. /etc/xinetd.d/daytime-stream
  53. /etc/xinetd.d/discard-dgram
  54. /etc/xinetd.d/discard-stream
  55. /etc/xinetd.d/echo-dgram
  56. /etc/xinetd.d/echo-stream
  57. /etc/xinetd.d/tcpmux-server
  58. /etc/xinetd.d/time-dgram
  59. /etc/xinetd.d/time-stream
  60. /usr/lib/systemd/system/xinetd.service
  61. /usr/sbin/xinetd
  62. /usr/share/doc/xinetd-2.3.15
  63. /usr/share/doc/xinetd-2.3.15/CHANGELOG
  64. /usr/share/doc/xinetd-2.3.15/COPYRIGHT
  65. /usr/share/doc/xinetd-2.3.15/README
  66. /usr/share/doc/xinetd-2.3.15/empty.conf
  67. /usr/share/doc/xinetd-2.3.15/sample.conf
  68. /usr/share/man/man5/xinetd.conf.5.gz
  69. /usr/share/man/man5/xinetd.log.5.gz
  70. /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。

  1. systemctl start telnet.socket xinetd
  2. systemctl enable telnet.socket xinetd
  3. systemctl status telnet.socket xinetd

6、查看服务监听端口

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

四、Telnet远程连接测试

1、创建用户xybdiy

  1. [root@master ~]# useradd xybdiy
  2. [root@master ~]# passwd xybdiy
  3. Changing password for user xybdiy.
  4. New password: 
  5. BAD PASSWORD: The password is a palindrome
  6. Retype new password: 
  7. passwd: all authentication tokens updated successfully.

2、使用xybdiy用户telnet登录

  1. telnet 192.168.200.11
  3. Kernel 3.10.0-1160.53.1.el7.x86_64 on an x86_64
  4. master login: xybdiy
  5. Password:
  6. [xybdiy@master ~]$ su -
  7. Password:
  8. Last login: Tue Feb 22 12:39:35 CST 2022 on pts/1
  9. Last failed login: Tue Feb 22 12:52:02 CST 2022 on pts/2
  10. There was 1 failed login attempt since the last successful login.
  11. [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

  1. 1️⃣# 修改login文件
  2.  vim /etc/pam.d/login
  3.  注释这一行文件
  4.  #account    required     pam_nologin.so
  5. 按:wq保存退出。
  7. 2️⃣# 注释掉securetty文件
  8. mv /etc/securetty /etc/securetty.bak
  1. C:\Users\xybdiy>telnet 192.168.200.11
  3. Kernel 3.10.0-1160.53.1.el7.x86_64 on an x86_64
  4. master login: root
  5. Password:
  6. Last failed login: Tue Feb 22 13:59:24 CST 2022 from ::ffff:192.168.200.2 on pts/1
  7. There was 1 failed login attempt since the last successful login.
  8. Last login: Tue Feb 22 13:45:55 on pts/2
  9. [root@master ~]#
  1. [root@master ~]# telnet localhost
  2. Trying ::1...
  3. Connected to localhost.
  4. Escape character is '^]'.
  6. Kernel 3.10.0-1160.53.1.el7.x86_64 on an x86_64
  7. master login: root
  8. Password: 
  9. Last login: Tue Feb 22 14:11:49 from ::ffff:192.168.200.2
  10. [root@master ~]#

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