要使用CURL检查MySQL端口是否开放，可以按照以下步骤操作：

1、打开命令行终端（Windows下为cmd，Linux和Mac下为Terminal）。

2、输入以下命令，将your_mysql_host替换为你的MySQL服务器地址，将your_username替换为你的MySQL用户名，将your_password替换为你的MySQL密码，将3306替换为你的MySQL端口号（如果不同的话）：

curl v http1.1 "http://your_mysql_host:3306/" user your_username:your_password

3、观察输出结果，如果端口开放，你将看到类似以下的输出：

Rebuilt URL to: http://your_mysql_host:3306/
  Trying your_mysql_host...
TCP_NODELAY set
Connected to your_mysql_host (your_mysql_host) port 3306 (#0)
> GET / HTTP/1.1
> Host: your_mysql_host:3306
> UserAgent: curl/7.64.1
> Accept: */*
> Authorization: Basic your_base64_encoded_username_and_password
>
< HTTP/1.1 401 Unauthorized
< Server: nginx/1.14.0 (Ubuntu)
< Date: Wed, 09 Jun 2021 08:23:41 GMT
< ContentType: text/html; charset=UTF8
< ContentLength: 202
< Connection: keepalive
< WWWAuthenticate: Basic realm="Restricted"
< XContentTypeOptions: nosniff
< XXSSProtection: 1; mode=block
< XFrameOptions: SAMEORIGIN
< ETag: W/"1424B5AOg"
< CacheControl: maxage=0, mustrevalidate, nocache, nostore
< XRequestId: f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8f9a7e8f8
< XRuntime: 0.000000
< XPoweredBy: PHP 7.2.240ubuntu0.16.04.1
<
Ignoring the responsebody
Connection #0 to host your_mysql_host left intact

4、如果端口未开放，你将看到类似以下的输出：

Rebuilt URL to: http://your_mysql_host:3306/
  Trying your_mysql_host...
TCP_NODELAY set
connect to your_mysql_host port 3306 failed: Connection refused
Failed to connect to your_mysql_host port 3306: Connection refused
Closing connection 0

通过观察输出结果，你可以判断MySQL端口是否开放。