I'm have a strange situation with Joomla. I need Joomla usernames to be synced with usernames on a Linux system. That part is taken care of, but there is another issue. Joomla allows blank spaces and the @ symbol in usernames. Those symbols are not compatible with the way Linux handles usernames.

Is there a way to prevent those symbols from being used during registration without modifying the Joomla core?

Second question. Is there a way to limit Joomla usernames to min. 4 characters max. 8 characters?