Top 4 Must have Linux

1.  Kali Linux

Kali Linux is an advanced penetration testing tool that should be a part of every security professional’s toolbox. Penetration testing involves using a variety of tools and techniques to test the limits of security policies and procedures. What Kali has done is collect just about everything you’ll need in a single CD. It includes more than 300 different tools, all of which are open source and available on GitHub.
          Download it from here

2. BackBox Linux

BackBox is a Linux distribution based on Ubuntu. It has been developed to perform penetration tests and security assessments. Designed to be fast, easy to use and provide a minimal yet complete desktop environment, thanks to its own software repositories, always being updated to the latest stable version of the most used and best known ethical hacking tools
   Download it from here

3.NodeZero Linux

Penetration testing and security auditing requires specialist tools.The natural path leads us to collecting them all in one handy place. However how that collection is implemented can be critical to how you deploy effective and robust testing.
All though NodeZero Linux can be used as a “Live System” for occasional testing, its real strength comes from the understanding that a tester requires a strong and efficient system. This is achieved in our belief by working at a distribution that is a permanent installation, that benefits from a strong selection of tools, integrated with a stable linux environment.
        Download it from here

4. Samurai Web Testing Framework

The Samurai Web Testing Framework is a live linux environment that has been pre-configured to function as a web pen-testing environment. The CD contains the best of the open source and free tools that focus on testing and attacking websites. In developing this environment, we have based our tool selection on the tools we use in our security practice. We have included the tools used in all four steps of a web pen-test.
   Download it from here