Ubuntu16.04+crontab 定时任务不执？

crontab -l 显示任务为:

* * * * * php ~/Code/www/artisan schedule:run >> /dev/null 2>&1

Kernel代码部分为：

$schedule->command('check_article');

定时任务代码为:

$now = new Carbon('2017-06-08 00:00:00');
$day = $now->toDateString();
$tomorrow = new Carbon('2017-06-09');
$tomorrow = $tomorrow->toDateString();

$data =  Article::where('ptime', '>=',$day)
    ->where('ptime', '<', $tomorrow)
    ->where('is_check', '>', 0)
    ->get()->toArray();
if(count($data)<=0){
    $res = Article::where('ptime', '>=',$day)
        ->where('ptime', '<', $tomorrow)->count();
    $limit = $res*0.1 < 1 ? 1:  intval(round($res*0.1));
    $arr = Article::where('ptime', '>=',$day)
            ->where('ptime', '<', $tomorrow)
            ->orderBy(\DB::raw('RAND()'))
            ->limit($limit)
            ->get()->pluck('id')->toArray();
    Article::whereIn('id', $arr)->update(['is_check'=>1]);
}

我在命令控制台直接输入php ~/Code/www/artisan schedule:run 是可以执行的。但是crontab 的定时任务却不能执行。