1. 问题解决方法

1. 执行命令 php artisan cache:clear 并赋予 /storage 文件夹读写权限： chmod -R 777 storage；

2. 若在执行 php artisan cache:clear 时出现错误：Uncaught UnexpectedValueException: The stream or file "/storage/logs/laravel.log" could not be opened: failed to open stream: Permission denied in /vendor/monolog/monolog/src/Monolog/Handler/StreamHandler.php:87，需要赋予 /storage/log 读写权限： chmod -R 777 storage/logs；

3. 此时再执行 php artisan cache:clear，若继续出错：[ErrorException] file_put_contents(/bootstrap/cache/services.php): failed to open stream: Permission denied，需要赋予 bootstrap/cache 读写权限：chmod -R 777 bootstrap/cache；

4. 再执行 php artisan cache:clear，若仍然出错：[PDOException] SQLSTATE[HY000] [1045] Access denied for user 'xxx'@'127.0.0.1' (using password: YES)，则需要查看 laravel 的数据库配置是否正确。

2. 参考

1. laravel框架中提示错误：file_put_contents(/): failed to open stream: Permission denied – 百度知道

2. Laravel 5 migration error – stackoverflow