参考，
鳥哥私房菜 - 第七章、網路安全與主機基本防護：限制埠口, 網路升級與 SELinux
7.3.3 埠口与服务的启动/关闭及开机时状态设定
我们知道系统的 Telnet 服务通常是以 super daemon 来控管的，请您启动您系统的 telnet 试看看。
1 要启动 telnet 首先必须要已经安装了 telnet 的服务器才行，所以请先以 rpm 查询看看是否有安装 telnet-server 呢？ 『rpm -qa | grep telnet-server'如果没有安装的话，请利用原版光盘来安装，或者使用'yum install telnet-server'安装一下先;
bash
root@www:/etc/yum.repos.d# rpm -qa |grep telnet
<===发现本机没有安装telnet
##安装该软件
root@www:/etc/yum.repos.d# yum install telnet-server
上次元数据过期检查：0:13:37 前，执行于 2025年05月21日 星期三 16时37分46秒。
依赖关系解决。
==============================================================================================================================================================
软件包 架构 版本 仓库 大小
==============================================================================================================================================================
安装:
telnet-server x86_64 1:0.17-94.el10 TCappstream 38 k
事务概要
==============================================================================================================================================================
安装 1 软件包
总下载：38 k
安装大小：54 k
确定吗？[y/N]： y
下载软件包：
telnet-server-0.17-94.el10.x86_64.rpm 33 kB/s | 38 kB 00:01
--------------------------------------------------------------------------------------------------------------------------------------------------------------
总计 33 kB/s | 38 kB 00:01
运行事务检查
事务检查成功。
运行事务测试
事务测试成功。
运行事务
准备中 : 1/1
安装 : telnet-server-1:0.17-94.el10.x86_64 1/1
运行脚本: telnet-server-1:0.17-94.el10.x86_64 1/1
已安装:
telnet-server-1:0.17-94.el10.x86_64
完毕！
###查询到软件已安装
root@www:/etc/yum.repos.d# rpm -qa|grep telnet-server
telnet-server-0.17-94.el10.x86_64
root@www:/etc/yum.repos.d# yum info telnet-server
上次元数据过期检查：0:14:11 前，执行于 2025年05月21日 星期三 16时37分46秒。
已安装的软件包
名称 : telnet-server
时期 : 1
版本 : 0.17
发布 : 94.el10
架构 : x86_64
大小 : 54 k
源 : telnet-0.17-94.el10.src.rpm
仓库 : @System
来自仓库 : TCappstream
概况 : The server program for the Telnet remote login protocol
URL : http://web.archive.org/web/20070819111735/www.hcs.harvard.edu/~dholland/computers/old-netkit.html
协议 : BSD-3-Clause AND BSD-4-Clause AND BSD-4-Clause-UC
描述 : 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/telnet2 查询服务状态，并启动服务
bash
###查询服务状态
root@www:/etc/yum.repos.d# systemctl list-unit-files|grep telnet
telnet@.service static -
telnet.socket disabled disabled
root@www:/etc/yum.repos.d# systemctl status telnet@.service
Failed to get properties: Unit name telnet@.service is neither a valid invocation ID nor unit name.
root@www:/etc/yum.repos.d# systemctl status telnet.socket
○ telnet.socket - Telnet Server Activation Socket
Loaded: loaded (/usr/lib/systemd/system/telnet.socket; disabled; preset: disabled)
Active: inactive (dead)
Docs: man:telnetd(8)
Listen: [::]:23 (Stream)
Accepted: 0; Connected: 0;
###启动服务
root@www:/etc/yum.repos.d# systemctl start telnet.socket
###软件服务已经启动了
root@www:/etc/yum.repos.d# systemctl status telnet.socket
● telnet.socket - Telnet Server Activation Socket
Loaded: loaded (/usr/lib/systemd/system/telnet.socket; disabled; preset: disabled)
Active: active (listening) since Wed 2025-05-21 16:53:47 CST; 1s ago
Invocation: 0c194d99f5884f2295db2d68cff3f3ab
Docs: man:telnetd(8)
Listen: [::]:23 (Stream)
Accepted: 0; Connected: 0;
Tasks: 0 (limit: 200560)
Memory: 8K (peak: 256K)
CPU: 944us
CGroup: /system.slice/telnet.socket
5月 21 16:53:47 www.cici.titi systemd[1]: Listening on telnet.socket - Telnet Server Activation Socket.
###查询验证1
root@www:/etc/yum.repos.d# systemctl --state=loaded,active,listening --type=socket|grep telnet
telnet.socket loaded active listening Telnet Server Activation Socket
###查询验证2
root@www:/etc/yum.repos.d# systemctl status telnet.socket --state=loaded,active,listening --type=socket
● telnet.socket - Telnet Server Activation Socket
Loaded: loaded (/usr/lib/systemd/system/telnet.socket; disabled; preset: disabled)
Active: active (listening) since Wed 2025-05-21 16:53:47 CST; 1 day 3h ago
Invocation: 0c194d99f5884f2295db2d68cff3f3ab
Docs: man:telnetd(8)
Listen: [::]:23 (Stream)
Accepted: 0; Connected: 0;
Tasks: 0 (limit: 200560)
Memory: 8K (peak: 256K)
CPU: 944us
CGroup: /system.slice/telnet.socket
5月 21 16:53:47 www.cici.titi systemd[1]: Listening on telnet.socket - Telnet Server Activation Socket.
###查询验证3
root@www:/etc/yum.repos.d# systemctl list-units telnet.socket
UNIT LOAD ACTIVE SUB DESCRIPTION
telnet.socket loaded active listening Telnet Server Activation Socket
Legend: LOAD → Reflects whether the unit definition was properly loaded.
ACTIVE → The high-level unit activation state, i.e. generalization of SUB.
SUB → The low-level unit activation state, values depend on unit type.
1 loaded units listed. Pass --all to see loaded but inactive units, too.
To show all installed unit files use 'systemctl list-unit-files'.
###查询验证4
root@www:/etc/yum.repos.d# systemctl list-units |grep telnet
telnet.socket loaded active listening Telnet Server Activation Socket3 利用 netstat -tnlp 察看是否有啟動 port 23 呢？
bash
###已启动
root@www:/etc/yum.repos.d# netstat -tnlp |grep 23
tcp6 0 0 :::23 :::* LISTEN 1/systemd xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx