Nowadays operating systems are inseparable part of computer systems. Real-time operating systems (RTOS) are a special kind of operating systems that their main goal is to operate correctly and provide correct and valid results in a bounded and predetermined time. RTOSs are widely used in safety-critical domains. In these domains all the system’s requirements should be met and a catastrophe occurs if the system fails. Hence, fault tolerance is an essential requirement of RTOSs employed in safety-critical domains. In the past decades, several fault tolerance techniques have been proposed to protect different parts of an RTOS against faults and errors. In this paper, after presenting primary concepts of RTOSs, some features of these operating systems are reviewed and then a number of fault tolerance techniques that can be applied to each feature and their impact on system reliability is investigated. The main contribution of this work is to review and categorize several fault tolerance techniques applicable to RTOSs based on the operating system’s features.

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