Is the game must be free,or can not do it at all?
Yes, you can distribute proprietary software through Ubuntu by joining the Ubuntu Application Developer programme. In some cases the software is provided without a charge, and the developer makes money through advertising or upsells. In other cases a software license is sold to the user giving them rights to the software. Both systems are allowed in the Developer Programme.
http://developer.ubuntu.com/publish/commercial-software-faqs/
