public function remoteCommand($url = 'http://www.baidu.com')
    {
        $timestamp = $this->_getRemoteTimestamp($url);
        if ($timestamp === false) {
            return $this->console->error(['fetch remote timestamp failed: `:url`', 'url' => $url]);
        } else {
            $this->console->writeLn(date('Y-m-d H:i:s', $timestamp));
            return 0;
        }
    }