安装nc命令

    1. yum install nmap-ncat.x86_64  -y

    检测端口是否打开：nc -zuv ip 端口

    # nc -zuv 127.0.0.1 1812
Ncat: Version 7.50 ( https://nmap.org/ncat )
Ncat: Connected to 127.0.0.1:1812.
Ncat: UDP packet sent successfully
Ncat: 1 bytes sent, 0 bytes received in 2.03 seconds.