php code to zip and auto download a file. Works in Windows but not in Ubuntu

Question

I've got a project about showing all files of root directory in a list and the user can browse through files-directories, search a file by name,with the button downloadAll he can download all files at the current list.To make the downloadAll button work I use downloadAll.php code which by getting the current directory can create a zip file and auto download it. It works fine in windows. I'm trying to run the same project at linux but in that case it downloads an empty zipped file. Also when I try to open it this message appears:

Archive:  /tmp/archived_name.zip
[/tmp/archived_name.zip]
  End-of-central-directory signature not found.  Either this file is not
  a zipfile, or it constitutes one disk of a multi-part archive.  In the
  latter case the central directory and zipfile comment will be found on
  the last disk(s) of this archive.
zipinfo:  cannot find zipfile directory in one of /tmp/archived_name.zip or
          /tmp/archived_name.zip.zip, and cannot find /tmp/archived_name.zip.ZIP, period.

downloadZip.php:

<?php
if ((isset($_GET['currentdirectory'])) && ($_GET['currentdirectory']!="")){
    $the_folder = $_GET['currentdirectory']; 
}
else {
    $the_folder = "/var/www/my_project";
}

    $the_folder1 = $the_folder;

$zip_file_name = 'archived_name.zip';

$download_file= true;

class FlxZipArchive extends ZipArchive {

    public function addDir($location, $name) {
        $this->addEmptyDir(str_replace("./","",$name));

        $this->addDirDo($location, str_replace("./","",$name));
    } 

    private function addDirDo($location, $name) {
        $name .= '/';
        $location .= '/';

        $dir = opendir ($location);
        while ($file = readdir($dir))
        {
            if ($file == '.' || $file == '..') continue;

            $do = (filetype( $location . $file) == 'dir') ? 'addDir' : 'addFile';

                $this->$do($location . $file, str_replace("./","",$name) . $file);
        }
    } 
}

$za = new FlxZipArchive;
$res = $za->open($zip_file_name, ZipArchive::CREATE);
if($res === TRUE) 
{
    $za->addDir($the_folder1, basename($the_folder1));
    $za->close();
}
else  { echo 'Could not create a zip archive';}

if ($download_file)
{
    ob_get_clean();
    header("Pragma: public");
    header("Expires: 0");
    header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
    header("Cache-Control: private", false);
    header("Content-Type: application/zip");
    header("Content-Disposition: attachment; filename=" . basename($zip_file_name) . ";" );
    header("Content-Transfer-Encoding: binary");
    header("Content-Length: " . filesize($zip_file_name));
    readfile($zip_file_name);
}
unlink("archived_name.zip");
?>