Mkdir工作不正常 - debian中的权限问题?

my mkdir() function is not working properly on my debian webserver. I have tested this code and it works perfectly fine on my localhost, however it didnt create the directory once I tested it on my server and threw no error or exception.

That's the only piece of the code that isn't working.

$url = "../files/object/" . $this->id;

        if (!file_exists($url)) {
            mkdir($url, 0777, true);    
        } 

All folders are created and the path is correct aswell.

I am aware that this has been asked before, however I could not find a proper solution.

What I want to do: User creates an object => unique directory (name equals id) gets created for file upload