Switch root user:
1. Execute the command: yum install xinetd
2. Execute the command: yum install telnet
3. Execute the command: yum install telnet-server
4. Open the telnet command, by modifying the configuration file (it is closed by default), execute the command: vi /etc/xinetd.d/telnet
Modify disable = yes to disable = no
5. Execute the command: service xinetd restart
6. Verify and execute the command: telnet www.baidu.com 443
