The secure OS means the system that defends and blocks the prospective hacking by adding various security functions such as access control, user authentication, audit and trail, and anti-hacking to Linux kernel. To protect important information from threatening elements, it is essential to establish the security system that satisfies the systematic security policy and the security requirements. In this paper, we analyzed the existing studies about the current secure OS, security module and SELinux, and suggested Linux access control module that uses the user discriminating authentication, security authority inheritance of subjects and objects, reference monitor and MAC class process and real-time audit trailing using DB. In addition, by restricting the root authority, the access to security level files without any access authority will be blocked. Malicious hacking can be thoroughly blocked thanks to real-time audit trailing using DB.