在sudo权限下执行如下命令即可安装telnet

yum -y install xinetd telnet telnet-server

[oracle@centos downloads]$ sudo yum -y install xinetd telnet telnet-server
[sudo] password for oracle: 
已加载插件：fastestmirror, langpacks
Loading mirror speeds from cached hostfile
 * base: mirrors.nwsuaf.edu.cn
 * extras: mirrors.cqu.edu.cn
 * updates: mirrors.cqu.edu.cn
正在解决依赖关系
--> 正在检查事务
---> 软件包 telnet.x86_64.1.0.17-60.el7 将被 安装
---> 软件包 telnet-server.x86_64.1.0.17-60.el7 将被 安装
---> 软件包 xinetd.x86_64.2.2.3.15-13.el7 将被 安装
--> 解决依赖关系完成

依赖关系解决

=====================================================================================================================
 Package                        架构                    版本                             源                     大小
=====================================================================================================================
正在安装:
 telnet                         x86_64                  1:0.17-60.el7                    base                   63 k
 telnet-server                  x86_64                  1:0.17-60.el7                    base                   40 k
 xinetd                         x86_64                  2:2.3.15-13.el7                  base                  128 k

事务概要
=====================================================================================================================
安装  3 软件包

总下载量：232 k
安装大小：429 k
Downloading packages:
(1/3): telnet-server-0.17-60.el7.x86_64.rpm                                                   |  40 kB  00:00:00     
(2/3): xinetd-2.3.15-13.el7.x86_64.rpm                                                        | 128 kB  00:00:00     
(3/3): telnet-0.17-60.el7.x86_64.rpm                                                          |  63 kB  00:00:00     
---------------------------------------------------------------------------------------------------------------------
总计                                                                                 210 kB/s | 232 kB  00:00:01     
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
  正在安装    : 1:telnet-server-0.17-60.el7.x86_64                                                               1/3 
  正在安装    : 2:xinetd-2.3.15-13.el7.x86_64                                                                    2/3 
  正在安装    : 1:telnet-0.17-60.el7.x86_64                                                                      3/3 
  验证中      : 1:telnet-0.17-60.el7.x86_64                                                                      1/3 
  验证中      : 2:xinetd-2.3.15-13.el7.x86_64                                                                    2/3 
  验证中      : 1:telnet-server-0.17-60.el7.x86_64                                                               3/3 

已安装:
  telnet.x86_64 1:0.17-60.el7        telnet-server.x86_64 1:0.17-60.el7        xinetd.x86_64 2:2.3.15-13.el7       

完毕！