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Linux Operating System

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Linux Operating System

Created: 2025-11-25 Tags: operating-systems linux unix open-source

Description

Linux is an open-source, Unix-like operating system that powers most servers, cloud infrastructure, and security tools. Mastery of Linux is essential for cybersecurity professionals.

Key Concepts

Major Distributions

  • Debian-based: Ubuntu, Kali Linux, Parrot OS
  • Red Hat-based: RHEL, CentOS, Fedora
  • Arch-based: Arch Linux, Manjaro
  • SUSE-based: openSUSE, SUSE Enterprise
  • Security-focused: Kali Linux, Parrot Security OS

Core Components

  • Kernel: Core of the operating system
  • Shell: Command interpreter (bash, zsh, sh)
  • Init system: systemd, SysV, Upstart
  • Package managers: apt, yum, dnf, pacman
  • File system: ext4, XFS, Btrfs

File System Hierarchy

/       - Root directory
/bin    - Essential binaries
/etc    - Configuration files
/home   - User home directories
/var    - Variable data (logs)
/tmp    - Temporary files
/opt    - Optional software
/usr    - User programs

Security Features

Built-in Security

  • SELinux: Security-Enhanced Linux (mandatory access control)
  • AppArmor: Application security framework
  • iptables/nftables: Firewall rules
  • sudo: Controlled privilege escalation
  • File permissions: User/Group/Other permissions
  • SSH: Secure remote access

Security Advantages

  • Open source code review
  • Principle of least privilege by default
  • Strong user separation
  • Powerful command-line tools
  • Extensive security tools available

Essential Commands

# File operations
ls, cd, pwd, cp, mv, rm, mkdir
find, grep, cat, less, head, tail
 
# Permissions
chmod, chown, chgrp
 
# System management
ps, top, htop, systemctl
service, journalctl
 
# Network
ifconfig, ip, netstat, ss
curl, wget
 
# Package management
apt update/install (Debian)
yum/dnf install (Red Hat)
 
# User management
useradd, usermod, passwd
sudo, su

Security Hardening

  • Regular updates (apt update && apt upgrade)
  • Disable root login via SSH
  • Use SSH keys instead of passwords
  • Configure firewall (iptables/ufw)
  • Enable SELinux/AppArmor
  • Minimal installation (reduce attack surface)
  • Regular security audits
  • Implement fail2ban for brute force protection

Practical Applications

  • Penetration testing with Kali Linux
  • Server administration and hardening
  • Security tool development
  • Incident response and forensics
  • Network monitoring and analysis

Learning Resources

  • Man pages (man command)
  • /usr/share/doc documentation
  • TryHackMe - Linux rooms
  • HackTheBox - Linux machines

Back to: 00-MOC-Cybersecurity-Roadmap

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