Also, One problem voiced by potential open source users is the lack of a central resource to provide support similar to a embedded computer software vendor. After a life-cycle analysis and the “sticker shock” associated with the cost of a commercial OS, designers usually also consider “free” open source operating systems. Although open source software eliminates some initial cost problems, there are still significant issues that must be addressed. Open source software is not in the public domain and users must adhere to specific rules set forth in individual licenses that may force designers to reveal the source code to proprietary software. Even with these hurdles, open source operating systems are widely used in embedded design. Small footprint is function-handy. An added consideration when selecting an OS is the trade-off between embedded computer the initial hardware footprint required and the ability to add features when updates become necessary. The OS must be scalable so that users can select just those portions or features of the software system that they need.
refer to: http://embedded-computing.com/articles/choose-right-embedded-operating-system/