With decades development, RTLinux/GPL was widespread applied to both scientific research realm and industry. RTLinux/GPL has made a grate success in these realm, But has little affection in education, especially the undergraduate education. Most of the RTLinux/GPL documentation are focus on the practicability, other than emphasizing the basic RealTime Operatiing System theory. So RTLinux/GPL is very hard to applied to education realm. This article aimed at RTOS education, containing real time principle of RTLinux/GPL and the RTLinux/GPL modules implementation in detail. It would make the realtime operating system learning process easier with both theory and real source code analyze, and would attract more people to interested in RTLinux/GPL. This article presented RTLinux/GPL principle and implementation details, containning realtime clock, interrupt, realtime schedule strategy. We hope this article can help people to apprehend RTOS, especially the RTLinux/GPL.