CyberSecurity & DevSecOps Expert: Develop, PenTest, and Deploy Secure Applications

THEORETICAL RECAP On Linux, every process runs with the privileges of a user and its groups. The principle of least privilege dictates that an account should hold only the permissions strictly required for its tasks—nothing more. A pentester frequent...

Advanced user and sudoer management is a cornerstone of Linux security. On a Linux system, every process and every file is tied to an identity. Understanding how users, groups, and privilege elevation work allows you to reduce the attack surface, app...

THEORETICAL RECAP A Bash script is just a text file until you grant it execute permission and provide an interpreter. The shebang line (#!/bin/bash) on the first line tells the system which interpreter to use. Permissions are managed with chmod: chmo...

Scripting is one of the most powerful tools a security professional has. A well-written Bash or Python script can automate reconnaissance, parse thousands of log lines, back up critical files, or orchestrate a deployment. But a poorly written script ...

THEORETICAL RECAP The /etc directory is the heart of Linux system configuration. It contains critical files: user accounts (/etc/passwd, /etc/shadow), network settings, service configurations, firewall rules, and repository definitions you manipulate...

Bash (Bourne Again Shell) is the default command interpreter on most Linux distributions. Writing scripts in Bash allows you to automate repetitive tasks, chain together the network and system tools you have already studied (ip, ss, nmap, apt, system...

On a Linux system, software is installed and updated through package managers such as apt (Debian, Ubuntu) or yum/dnf (Red Hat, CentOS, Fedora). These package managers download software from repositories. A repository is a server that hosts packages ...

THEORETICAL RECAP Before any penetration test or network analysis, you need a reconnaissance toolkit. Two tools are foundational: nmap and Wireshark. Nmap (Network Mapper) is an active scanner: it sends crafted packets to hosts to discover live machi...

Package management is one of the most important skills for anyone administering or securing a Linux system. A package is a compressed archive that contains a program, its libraries, configuration files, and metadata describing what the software needs...

THEORETICAL RECAP Documenting network status means capturing a reliable snapshot of what your Linux host exposes and communicates on the network at a given moment. The core mental model is a layered inventory: interfaces (link and IP configuration), ...

THEORETICAL RECAP A network interface is a connection point between your machine and a network. On Linux, interfaces such as 'lo' (loopback, 127.0.0.1), 'eth0' or 'enp0s3' (wired), and 'wlan0' (wireless) each carry one or more IP addresses. A port is...

In the previous chapters you learned to manage processes, signals, and services with systemd. A running service almost always listens on the network, so the next logical step is to inspect the local network configuration and the network activity of y...

When a Linux service fails to start, crashes unexpectedly, or behaves in an unexpected way, you need a systematic method to diagnose the problem. On modern Linux distributions, services are managed by systemd, and their logs are collected by a compon...

THEORETICAL RECAP On modern Linux systems, systemd is the init system and service manager (PID 1). A 'service' is a unit described by a unit file (usually ending in .service) located under /lib/systemd/system/ or /etc/systemd/system/. The core mental...

After learning to manage processes, permissions, and signals, the next step is to understand how a modern Linux system starts, supervises, and stops the services that run in the background. On most current distributions (Debian, Ubuntu, Red Hat, Cent...

THEORETICAL RECAP A signal is an asynchronous software interrupt sent to a process by the kernel, another process, or the user. It tells the process something happened and, unless caught or ignored, triggers a default action. Each signal has a name a...

THEORETICAL RECAP On Linux, a process is a running instance of a program, identified by a unique PID (Process ID) and linked to its parent through a PPID. Each process has an owner (the user who launched it), a state (Running, Sleeping, Zombie, Stopp...

Process management is one of the fundamental pillars of Linux system administration and security. Just as you have learned to control who can read or write files through permissions, you now need to understand who is running what on the system, with ...

This chapter serves as a comprehensive memo sheet and consolidation of everything covered in the Linux advanced permissions and navigation module. It is designed to be your go-to reference before moving on to security-focused practical exercises, and...

Building on your understanding of standard Linux permissions (read, write, execute for owner, group, and others), digital chmod notation, and ownership management with chown and chgrp, this lesson introduces three additional permission bits that go b...

**Theoretical Recap** In Linux, a shared folder is a directory accessed by multiple users or groups simultaneously. Securing it correctly means applying the right combination of ownership, permissions, and special bits to ensure that only authorized ...

THEORETICAL RECAP In Linux, every file and directory has two ownership attributes: a user owner and a group owner. These are distinct from permissions (which you have already practiced with chmod), but they work hand in hand: permissions only mean so...

When working in a Linux environment, especially in a security or DevSecOps context, permission errors are among the most frequently encountered issues. They can block scripts, prevent services from starting, expose sensitive files, or hide misconfigu...

**Theoretical Recap** Linux permissions are expressed numerically using an octal (base-8) system. Each file or directory has three permission groups: owner (user), group, and others. Each group is assigned a value based on three binary bits: read (r ...

**Theoretical Recap** File permissions in Linux are a foundational security mechanism. Every file and directory has three permission sets: owner (u), group (g), and others (o). Each set can carry three types of permissions: read (r), write (w), and e...