This document provides a quick reference guide for Linux security that includes definitions of common security terms, general security tips, and Linux security resources. It defines terms like buffer overflow, cryptography, denial of service, and port scanning. It offers tips such as using automatic package managers to update software, configuring firewalls and intrusion detection, and enforcing strong password policies. The document also lists various security-related websites, books, and open source tools that can aid in hardening Linux systems.