Worldwide IT industry is experiencing a rapid shift towards Service Oriented Architecture (SOA). As a response to the current trend, all the IT firms are adopting business models such as cloud based services which rely on reliable and highly available server platforms. Linux servers are known to be highly secure. Network security thus becomes a major concern to all IT organizations offering cloud based services. The fundamental form of attack on network security is Denial of Service. This paper focuses on fortifying the Linux server defence mechanisms resulting in an increase in reliability and availability of services offered by the Linux server platforms. To meet this emerging scenario, most of the organizations are adopting business models such as cloud computing that are dependant on reliable server platforms. Linux servers are well ahead of other server platforms in terms of security. This brings network security to the forefront of major concerns to an organization. The most common form of attacks is a Denial of Service attack. This paper focuses on mechanisms to detect and immunize Linux servers from DoS .