php代码压缩和自动下载一个文件.适用于Windows，但不适用于Ubuntu

我有一个项目，关于在列表中显示根目录的所有文件，用户可以浏览文件目录，按名称搜索文件，点击按钮downloadAll，他可以下载当前列表中的所有文件。为了使downloadAll按钮工作，我使用downloadAll.php代码，通过获取当前目录，可以创建一个zip文件并自动下载。它在windows中运行良好。我试图在linux上运行相同的项目，但在这种情况下，它会下载一个空的压缩文件。此外，当我试图打开它时，会出现以下消息：

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");
?>