版权声明：转载请注明出处，谢谢。 https://blog.csdn.net/butterfly5211314/article/details/84189912
环境：
CentOS release 6.10 (Final)
$ telnet 127.0.0.1
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
原因是系统上没开telnet服务，解决如下：
yum -y install xinetd telnet-server
service xinetd start
netstat -tlunp | grep 23
# 发现23端口还没被监听，说明telnet服务没开
修改配置文件()：
# 修改/etc/xinetd.d/telnet
# 将disable = yes 值改为no
disable = no
重启telnet服务
service xinetd restart
# 在本机测试, 发现可以成功
telnet 127.0.0.1
Trying 127.0.0.1...
Connected to 127.0.0.1.
...省略部分内容
如果是另一台机器访问有问题，如：
[[email protected]] $
telnet 192.168.31.42
Trying 192.168.31.42...
telnet: Unable to connect to remote host: No route to host
需要检查下防火墙23有没有开：
$ iptables -L -n
Chain INPUT (policy ACCEPT)
target prot opt source destination
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:8080
...省略部分内容
开放23端口
iptables -I INPUT 6 -p tcp --dport 23 -j ACCEPT
service iptables save
iptables -L -n
Chain INPUT (policy ACCEPT)
target prot opt source destination
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:8080
ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:23
...省略部分内容
再试发现就可以了：
[[email protected]] $ telnet 192.168.31.42
Trying 192.168.31.42...
Connected to 192.168.31.42.
...省略部分内容
欢迎补充指正