Overview
While practicing Linux fundamentals through OverTheWire-style wargames, I built a set of notes and small scripts focused on understanding how Linux systems behave from a security and attacker-observer perspective.
This post does not contain level solutions or flags. Instead, it documents concepts, techniques, and automation patterns that are directly applicable to:
- penetration testing,
- CTF-style challenges,
- and real-world Linux enumeration.
The goal is to show how to think, not what to solve.
Why OverTheWire Is Valuable for Security Learning
OverTheWire challenges force you to interact with Linux systems in constrained environments. You are often required to:
- extract information from unusual file formats,
- deal with strict permissions,
- observe ephemeral system behavior,
- and automate repetitive tasks.
From a security perspective, this develops:
- strong command-line fluency,
- intuition for data leakage,
- and the habit of observing system behavior before acting.
Text Processing & Data Extraction
Many challenges revolve around extracting meaningful data from noisy or unfamiliar files. Tools such as cat, file, grep, awk, sed, cut, strings, base64, and xxd become essential.
Rather than memorizing commands, the key lesson is understanding data flow.
Typical pattern
command_producing_output | filter | transform | extract
This mindset maps directly to real-world enumeration and log analysis.
Filesystem Enumeration & Permissions
Restricted permissions are common in training labs and real systems.
Using find with permission filters allows identification of files that are readable, owned by specific users, or misconfigured:
find / -type f -readable ! -writable 2>/dev/null
This trains you to focus on misconfigurations rather than noise.
Processes & Local Networking
Commands such as ps, lsof, pwdx, nc, /dev/tcp, and openssl s_client help observe live system behavior.
These techniques are critical for:
- local enumeration,
- interacting with services,
- detecting unusual activity.
Automation Mindset with Bash
When tasks become repetitive, automation becomes mandatory.
Two small scripts created during these exercises illustrate this mindset.
Script: Multi-layer Decompression Helper
CTF challenges often include files compressed multiple times.
Core idea
- List compressed contents.
- Extract inner file.
- Repeat while extraction succeeds.
Simplified pseudocode
extract file
while file is compressed:
extract next layer
stop
This approach saves time and reduces errors during enumeration.
Script: Simple Process Monitor
This script compares process snapshots over time.
Simplified pseudocode
previous = process list
loop:
current = process list
show differences
previous = current
Useful for detecting short-lived or unexpected processes.
Ethical Considerations
This material is intended strictly for learning and defensive awareness.
- No challenge solutions are disclosed.
- No flags are shared.
- All testing should be performed on authorized systems.
Repository Reference
Full notes and scripts are available here:
https://github.com/lameiro0x/bash-scripting-labs-OTW
Closing Thoughts
Strong Linux fundamentals are a force multiplier in security.
Understanding system behavior, data flow, and automation significantly improves effectiveness in both CTFs and real-world security work.