Force file download code works on localhost but does not work on real server in PHP

I'm php programmer of beginner. I have write code to download file of any type.

When I click on download link it goes to download.php file. I work on local server but not working on server.

My code is:

header('Content-Description: File Transfer');
        header('Content-Type: application/octet-stream');    //application/force-download
        header('Content-Disposition: attachment; filename='.basename($file));
        header('Content-Transfer-Encoding: binary');
        header('Expires: 0');
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Pragma: public');
        //header('Content-Length: ' . filesize($file));
        ob_clean();
        flush();
        readfile($file);
        exit();

Is my code wrong or does server need some settings?

---

by using code written by me. this problem is solved. if anybody have same issue. please try this code. it works for me very good.

$file_name ='../img/files'.DS.$_GET['file'];
if(is_file($file_name)) {
        if(ini_get('zlib.output_compression')) {
                ini_set('zlib.output_compression', 'ON');
        }
        switch(strtolower(substr(strrchr($file_name, '.'), 1))) {
                case 'pdf':  $mime = 'application/pdf'; break; // pdf files
                case 'zip':  $mime = 'application/zip'; break; // zip files
                case 'jpeg': $mime = 'image/jpeg'; break;// images jpeg
                case 'jpg':  $mime = 'image/jpg'; break;
                case 'mp3':  $mime = 'audio/mpeg'; break; // audio mp3 formats
                case 'doc':  $mime = 'application/msword'; break; // ms word
                case 'avi':  $mime = 'video/x-msvideo'; break;  // video avi format
                case 'txt':  $mime = 'text/plain'; break; // text files
                case 'xls':  $mime = 'application/vnd.ms-excel'; break; // ms excel
                default: $mime = 'application/force-download';
        }
    header('Content-Type:application/force-download');
        header('Pragma: public');       // required
        header('Expires: 0');           // no cache
        header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
        header('Last-Modified: '.gmdate ('D, d M Y H:i:s', filemtime ($file_name)).' GMT');
        header('Cache-Control: private',false);
        header('Content-Type: '.$mime);
        header('Content-Disposition: attachment; filename="'.basename($file_name).'"');
        header('Content-Transfer-Encoding: binary');
        //header('Content-Length: '.filesize($file_name));      // provide file size
        header('Connection: close');
        readfile($file_name);
        exit();
}