Magento comes with a built-in logging facility which can be enabled and configured in the back-end under System > Configuration > Developer. Alternatively you can enable the Developer Mode for the site to enable the log (on how to do this have a look at the index.php file). The exception log is always on.
Magento Comes with a built-in Logging Facility Which can be enabled and configured
Magento Comes with a built-in Logging Facility Which can be enabled and configured