When Linux is mentioned, usually General Purpose Operating System (GPOS) is related to it, but over time, the need to have the same benefits as Real-Time Operating System (RTOS) for Linux has become more stringent. The challenge for any real-time system is to meet the given timing constrains in spite of the number and type of random asynchronous events. This is no simple task and an extensive number of papers and researches were done on theory of the real-time systems. Another challenge for a real-time system would be to have an upper limit on latency, called a scheduling deadline. Depending on how systems meet this challenge, they can be split into hard, firm, and soft: