500 error code 原因

1. resource overload
2. too busy on server side
3. uploaded file size too big
4. bug: null pointer
5. file access permission
6. disk space full
7. .htaccess config php_flag display_errors 1

for 7, refer to :
https://stackoverflow.com/questions/17693391/500-internal-server-error-for-php-file-not-for-html

https://www.a2hosting.com/kb/developer-corner/php/500-internal-server-error-while-running-php

refer:
https://www.ionos.com/digitalguide/hosting/technical-matters/http-error-500-internal-server-error/

Permission error: The permissions of the main files and folders are not set correctly.
PHP timeout: The script tries to access an external resource and experiences a timeout.
Incorrect code in .htaccess: The structure in a .htaccess file could be wrong.
Error in syntax or code in CGI/Perl scripts: In some cases, scripts are incorrect. Paths, especially, can be misaligned.
PHP memory limit: A process exceeds memory and therefore cannot be executed correctly.

https://www.sejuku.net/blog/77760

1. .htaccess setting error
2. file permission
3. PHP configuration miss