带有 cron 的 Laravel 调度命令

我有命令log:demo，我使用命令成功从ssh控制台运行它：php artisan log:demo。

现在我需要创建 cron 作业，它没关系，但是当 cron 启动命令时，我会得到 laravel.log：

> [2016-03-22 21:45:01] local.ERROR: exception 'ErrorException' with message 'Invalid argument supplied for foreach()' in /home/agroagro/public_html/vendor/symfony/console/Input/ArgvInput.php:283
Stack trace:
#0 /home/agroagro/public_html/vendor/symfony/console/Input/ArgvInput.php(283): Illuminate'Foundation'Bootstrap'HandleExceptions->handleError(2, 'Invalid argumen...', '/home/agroagro/...', 283, Array)
#1 /home/agroagro/public_html/vendor/symfony/console/Application.php(790): Symfony'Component'Console'Input'ArgvInput->hasParameterOption(Array)
#2 /home/agroagro/public_html/vendor/symfony/console/Application.php(117): Symfony'Component'Console'Application->configureIO(Object(Symfony'Component'Console'Input'ArgvInput), Object(Symfony'Component'Console'Output'ConsoleOutput))
#3 /home/agroagro/public_html/vendor/laravel/framework/src/Illuminate/Foundation/Console/Kernel.php(107): Symfony'Component'Console'Application->run(Object(Symfony'Component'Console'Input'ArgvInput), Object(Symfony'Component'Console'Output'ConsoleOutput))
#4 /home/agroagro/public_html/artisan(35): Illuminate'Foundation'Console'Kernel->handle(Object(Symfony'Component'Console'Input'ArgvInput), Object(Symfony'Component'Console'Output'ConsoleOutput))
#5 {main}  

为什么手动调用命令有效，而 cron 不起作用？