// 代码使用 nesbot/carbon 包

// get last bootup time
exec('WMIC OS GET LastBootUpTime', $output);

$bootUpTime = current(explode('+', $output[1]));
$bootUpTime = Carbon::createFromFormat('YmdHis.u', $bootUpTime)->timestamp;

$bootedSeconds = Carbon::now()->timestamp - $bootUpTime;

echo "系统已运行：{$bootedSeconds} 秒";