Today's meeting provided a comprehensive introduction to the Linux operating system, covering everything from basic navigation to system hardening and rootkit detection. The session was designed to give members a solid foundation in preparation for more advanced cybersecurity topics.

Introduction to Linux

The presentation began with an introduction to Linux, an open-source operating system centered around a kernel that manages hardware resources like memory and storage. We discussed various distributions, ranging from server-oriented ones like Debian to security-focused distributions like Kali and Red Hat.

The Shell and Filesystem

We explored the structure of a shell prompt and practiced essential commands for navigation (cd, pwd), file listing (ls), and obtaining help (man, --help). We then reviewed the standard directory structure, including /bin for binaries, /etc for configuration files, and /home for user directories. We covered file manipulation commands (touch, rm, cp, mv) and the difference between hard links (additional names for data) and soft links (pointers to a file path). Members then learned how to interpret and modify file permissions (rwx) for owners, groups, and others using chmod, chown, and chgrp.

Process Management

We discussed global variables like PATH and how to customize the shell environment using the ~/.bashrc file. We introduced the "files" STDIN, STDOUT, and STDERR, along with techniques for redirection (>, 2>) and piping (|). We then examined the process lifecycle, identifying processes by their PID and monitoring system activity using commands like ps aux and pstree.

Linux Hardening

The meeting concluded with a focus on Linux hardening, which is critical for protecting systems against external threats. Key strategies discussed included:

• •The "Decisive 70%": Keeping software updated, disabling unused services, using minimal OS images, encrypting login/file transfers, and comprehensive logging.
• •Mitigation Techniques: Implementing the principle of least privilege, sandboxing applications, and utilizing security features like ASLR and NX.
• •Rootkit Detection: How rootkits hide by replacing standard binaries (like sshd) and how to defend against them using File Integrity Monitoring (FIM) tools like AIDE or more complex solutions like Wazuh.