CentOS开启Telnet：

参考：https://geekflare.com/telnet-command-not-found/

发现CentOS中没有telnet：

telnet
-bash: telnet: command not found

安装之：

yum -y install telnet

Win10中开启Telnet：

参考：https://www.crifan.com/win7_telnet_telnet_is_not_recognized_as_an_internal_or_external_command/

期间，发现win7中没有telnet：

C:\Users\CLi>telnet sjc004.hawkhost.com 2087
‘telnet’ is not recognized as an internal or external command,
operable program or batch file.

微软默认把telnet关闭了。

去开启即可。

Start >> Control Panel >> Programs And Features >> Turn Windows features on or off >> Check Telnet Client >> Hit OK