protected function getSysfs()
    {
        $mac = false;

        if (strtoupper(php_uname('s')) === 'LINUX') {
            $addressPaths = glob('/sys/class/net/*/address', GLOB_NOSORT);

            if (empty($addressPaths)) {
                return false;
            }

            array_walk($addressPaths, function ($addressPath) use (&$macs) {
                $macs[] = file_get_contents($addressPath);
            });

            $macs = array_map('trim', $macs);

            // remove invalid entries
            $macs = array_filter($macs, function ($mac) {
                return
                    // localhost adapter
                    $mac !== '00:00:00:00:00:00' &&
                    // must match  mac adress
                    preg_match('/^([0-9a-f]{2}:){5}[0-9a-f]{2}$/i', $mac);
            });

            $mac = reset($macs);
        }

        return $mac;
    }