当使用 Apache 作为服务器，使用 cgi 程序接收来自 web 端的访问时，出现如下错误：
Internal Server Error
The server encountered an internal error or misconfiguration and was unable to complete your request.
Please contact the server administrator, you@example.com and inform them of the time the error occurred, and anything you might have done that may have caused the error.
More information about this error may be available in the server error log.
debug 了好久，最后发现是自己的 cgi 程序——generate_license 没有可执行权限。这就很尴尬了，使用命令 chmod +x generate_license 即可解决。