public function chmod($files, $mode, $umask = 0000, $recursive = false)
    {
        foreach ($this->toIterable($files) as $file) {
            if (true !== @chmod($file, $mode & ~$umask)) {
                throw new IOException(sprintf('Failed to chmod file "%s".', $file), 0, null, $file);
            }
            if ($recursive && is_dir($file) && !is_link($file)) {
                $this->chmod(new \FilesystemIterator($file), $mode, $umask, true);
            }
        }
    }