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 ~]#
