protected function _getPidRecursive($ppid) {
		if (!$ppid) {
			return array();
		}
		$allPids = $pids = array_filter(preg_split('/\s+/', `ps -o pid --no-heading --ppid $ppid`));

		foreach ($pids as $pid) {
			$allPids = array_merge($allPids, $this->_getPidRecursive($pid));
		}
		return $allPids;
	}