1.需求
CI在linux上无法加载model
2.原因
因为linux区分大小写，且model文件名首字符要大写。
As said in the comments : Your model's filename must start with an uppercase. In your case, Ion_auth_model.php.
参考资料：http://stackoverflow.com/questions/28506163/troubleshooting-codeigniter-unable-to-locate-the-model-you-have-specified-e