Abstract: In order to balance response time and throughput and to ensure fair distribution of CPU time among process, Linux, as a time sharing system, schedules CPU time using fixed time slices, but it can not guarantee the high predictability requirements of real time task In order to improve the real time performance of Linux OS, the real time scheduling support in RFRTOS based on Linux is discussed The experiments on the modified OS show that the improvement gives a better result for applications with real time constraints than original Linux kernel and satisfies the need of soft real time