What Is PHP open_basedir Issue and How This Causes HTTP 500 Error?

The open_basedir is a function that defines the locations or paths from which PHP is authorized to access files using functions like gzopen() and fopen(). If a file or document defined by open_basedir which is outside of the paths is outside of the paths, then PHP will deny to open it in shared web hosting. 

              It cause the server for encountering an unexpected condition or configuration problem, that prevents it from fulfilling the request made by the browser or client and so the HTTP 505 error occurs.