Linux Basics for Hackers

Executive Summary: Why Linux Underpins All Cybersecurity

Whether you aspire to become a penetration tester, cloud security engineer, SOC incident responder, or bug bounty hunter, mastering the Linux operating system is non-negotiable. Over 90% of cloud workloads, web servers, C2 implants, and security appliances run on Linux distributions, with Kali Linux standing as the industry-standard OS for offensive operations.

Linux Basics for Hackers is a hands-on 240-page technical guide specifically crafted for aspiring cybersecurity professionals. Moving beyond graphical interfaces, this handbook teaches you how to command the Linux terminal with speed, script repetitive security tasks in Bash, audit system permissions for dangerous SUID misconfigurations, analyze network traffic, and maintain service persistence.

Deep Dive: Core Linux Security Engineering Topics

The handbook provides practical, terminal-driven instruction across five fundamental domains:

1. File Hierarchy Standard (FHS) & Text Processing

Navigating the Linux directory tree and manipulating unformatted log streams:

• Critical System Paths: Inspecting /etc/passwd, /etc/shadow, /var/log/auth.log, and volatile /proc memory virtual files.
• Stream Processing: Harnessing grep regex, awk field extraction, sed stream substitution, and cut to parse gigabytes of web logs.

2. File Permissions, SUID Bits & GTFOBins

Understanding access controls and local privilege escalation vectors:

• Octal Permission Masks: Calculating chmod 755 vs chmod 600 permissions for SSH private keys (`id_rsa`).
• SUID/SGID Abuse: Auditing binaries with the Set Owner User ID bit (e.g. find / -perm -4000 2>/dev/null) to exploit GTFOBins for root shell access.

3. Networking Utilities, Firewalls & Ncat

Auditing local network sockets and intercepting packet traffic:

• Socket Inspection: Listing active listening ports and process IDs using ss -tulpn or netstat -antp.
• Ncat Relays & Firewalls: Building encrypted TCP relays with ncat and creating packet filtering rules in iptables / ufw.

Field Engineering: Bash Security Automation Scripts

Chapter 7 of the handbook provides practical Bash automation scripts for network discovery and SUID privilege auditing:

#!/bin/bash
# Subnet Ping Sweeper & Port 80/443 Scanner

SUBNET="192.168.1"
LOGFILE="active_hosts.txt"
echo "[*] Starting Subnet Discovery Sweep on $SUBNET.0/24..." > $LOGFILE

for ip in $(seq 1 254); do
    TARGET="$SUBNET.$ip"
    # Send 1 ICMP Echo Request with 1 second timeout
    ping -c 1 -W 1 $TARGET > /dev/null 2>&1
    if [ $? -eq 0 ]; then
        echo "[+] Host Active: $TARGET" | tee -a $LOGFILE
        
        # Check HTTP Port 80
        (echo > /dev/tcp/$TARGET/80) >/dev/null 2>&1 && echo "    --> Port 80 (HTTP) OPEN" | tee -a $LOGFILE
        # Check HTTPS Port 443
        (echo > /dev/tcp/$TARGET/443) >/dev/null 2>&1 && echo "    --> Port 443 (HTTPS) OPEN" | tee -a $LOGFILE
    fi
done

echo "[*] Sweep Completed. Results saved to $LOGFILE"

#!/bin/bash
# SUID & System Capabilities Audit Script for Local PrivEsc

echo "=== DANGEROUS SUID BINARIES FOUND ==="
find / -perm -4000 -type f -exec ls -la {} \; 2>/dev/null | awk '{print $3, $4, $9}'

echo ""
echo "=== SYSTEM CAPABILITIES (getcap) ==="
getcap -r / 2>/dev/null

echo ""
echo "=== WRITABLE ETC / CRON PATHS ==="
ls -la /etc/crontab /etc/cron.* /etc/passwd /etc/shadow 2>/dev/null | grep "w"

Complete Table of Contents & Module Syllabus

• Module 01 Kali Linux Foundations & Terminal Navigation

  Pages 1–30
  Kali installation, shell navigation (`cd`, `ls`, `pwd`), environment variables, alias creation, and man pages.
• Module 02 Linux File System Hierarchy & Text Stream Processing

  Pages 31–60
  Exploring `/etc`, `/var/log`, `/proc`, and `/tmp`, text piping, regex searching with `grep`, `awk`, `sed`, and `cut`.
• Module 03 File Permissions, ACLs & SUID/SGID Security

  Pages 61–90
  Octal permission masks (`chmod`), user/group management (`chown`), SUID/SGID bits, POSIX Access Control Lists (`getfacl`).
• Module 04 Linux Network Configuration & Traffic Analysis

  Pages 91–120
  Network interface commands (`ip`, `ifconfig`), netstat/ss socket auditing, packet sniffing with `tcpdump`, and Ncat relays.
• Module 05 Package Repositories, Systemd Services & Daemons

  Pages 121–150
  APT package management, inspecting `/etc/apt/sources.list`, managing systemd unit files (`systemctl`), and service persistence.
• Module 06 Storage Partitioning, LUKS Encryption & System Logs

  Pages 151–180
  Disk partitioning (`fdisk`, `lsblk`), LUKS volume encryption, system logging (`rsyslogd`, `journalctl`), and log rotation.
• Module 07 Bash Shell Scripting for Security Automation

  Pages 181–210
  Writing Bash scripts, variables, loops (`for`/`while`), positional parameters, error handling, and automated network discovery.
• Module 08 Kernel Auditing, GTFOBins & Privilege Escalation

  Pages 211–240
  Identifying misconfigured SUID binaries, GTFOBins privilege escalation tricks, Linux kernel exploits, and hardening guidelines.

Who Should Read This Handbook?

This handbook is designed for cybersecurity aspirants and Linux users:

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