_____ _ _ _ _____ |_ _|__ _ __ _ __ ___ (_)_ __ __ _| | | ||___ / | |/ _ \ '__| '_ ` _ \| | '_ \ / _` | | |_ ||_ \ | | __/ | | | | | | | | | | | (_| | | _|___) | |_|\___|_| |_| |_| |_|_|_| |_|\__,_|_|_| |____/ OS
Learn Systems.
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SSH into real Linux containers. Capture real packets. Break things, fix things, prove mastery through action.
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SEE IT IN ACTION
Real Terminals. Real Challenges.
Every challenge drops you into a live Linux container via SSH. Explore the filesystem, fix broken configs, debug services, and prove your skills hands-on.
- Full SSH access to real Ubuntu containers
- Automatic watcher validates your solution in real-time
- Points awarded instantly, no manual review
Terminal 43 // Challenge: Find the Hidden File
$ ssh challenger@container
challenger@t43:~$ ls -la
total 16
drwxr-xr-x 3 challenger challenger 4096 Jan 1 00:00 .
drwxr-xr-x 3 root root 4096 Jan 1 00:00 ..
drwxr-xr-x 2 challenger challenger 4096 Jan 1 00:00 .hidden
-rw-r--r-- 1 challenger challenger 0 Jan 1 00:00 readme.txt
challenger@t43:~$ cat .hidden/flag.txt
T43{you_found_the_hidden_file}
✅ Challenge Solved! +100 points
HOW IT WORKS
Three Steps to Mastery
No videos. No quizzes. Just real systems and real commands.
STEP 01
SSH In
Launch a real Linux container and connect via SSH. Your own sandbox to explore, break, and fix.
STEP 02
Solve
Find the hidden file. Fix the broken config. Capture the packet. A watcher validates your work automatically.
STEP 03
Level Up
Earn points, unlock achievements, climb leaderboards. Track your journey from beginner to sysadmin.
SKILL DOMAINS
What You'll Learn
Real-world Linux skills organized into domains. Each domain maps to challenges you solve hands-on.
Access & Identity Compliance
5 challenges
Advanced Challenges & Capstone
9 challenges
Advanced Git
4 challenges
Asymmetric Encryption
4 challenges
Authorization & Privilege
4 challenges
Automated Scanning with OpenSCAP
5 challenges
Automation & Scripting
3 challenges
Backup & Recovery
4 challenges
Backup, Recovery & Snapshots
5 challenges
Beyond a Single Host
3 challenges
Boot & Init Failures
4 challenges
Branching
5 challenges
Bridges, Bonds & Virtual Interfaces
2 challenges
Building Images with Dockerfile
4 challenges
Capstone
9 challenges
Capstone -- Bring a Server to CIS Compliance and Prove It
3 challenges
Capstone -- Build a Router, Firewall, and VPN Gateway
4 challenges
Capstone -- Containerize and Ship a Multi-Service Application
3 challenges
Capstone -- Deploy, Secure, Back Up, and Tune a Production Datab
3 challenges
Capstone -- Fix the Broken Server
3 challenges
Capstone -- Harden and Defend a Compromised Server
3 challenges
Capstone -- Provision and Operate a Production Server
4 challenges
Capstone -- Run Your Own CA and Secure a Service End to End
3 challenges
Certificate Lifecycle
3 challenges
Certificates & X.509
3 challenges
CIS Benchmarks in Depth
4 challenges
Collaboration Workflows
3 challenges
Conditionals, Loops & Handlers
4 challenges
Container Networking
4 challenges
Container Security
4 challenges
Continuous Compliance
3 challenges
Core Application Protocols
6 challenges
CPU & Process Issues
4 challenges
Data & Persistence
4 challenges
Database Security
4 challenges
Detecting Compromise
4 challenges
Diagnosing Network Problems
6 challenges
Diagnostics & Observability
2 challenges
Digital Signatures
4 challenges
Disk & Filesystem Problems
4 challenges
Encoding vs Encryption vs Hashing
3 challenges
File Integrity & Change Detection
4 challenges
File Integrity & Configuration Drift
4 challenges
File Permissions & Access Control
6 challenges
File System & Storage
4 challenges
Filesystem & Navigation
2 challenges
Filesystem & Storage Security
4 challenges
Firewall Front-ends
4 challenges
Galaxy & Collections
3 challenges
Getting Started
5 challenges
GPG & the Web of Trust
4 challenges
Hardening Automation
4 challenges
Hardening Network Services
4 challenges
Hashing & Integrity
4 challenges
High Availability & Replication
4 challenges
How a Database Lives on Linux
3 challenges
Idempotency, Testing & Quality
4 challenges
Image Best Practices
3 challenges
Images & Layers
4 challenges
Import, Export & Migrations
4 challenges
Incident Response Basics
4 challenges
Indexes & Query Plans
4 challenges
Inspecting History
4 challenges
Installation & First Contact
4 challenges
Installing & Running Containers
4 challenges
Interacting with Containers
5 challenges
Interface & Address Configuration
4 challenges
IPv4 Addressing
5 challenges
IPv6
4 challenges
Kernel & Network Hardening
3 challenges
Kernel, Modules & Tuning
3 challenges
Keys in Practice
4 challenges
Log Forensics & Correlation
4 challenges
Logging & Auditing
4 challenges
Logging & Evidence for Audits
4 challenges
Logging & journald
4 challenges
Logical Volume Management (LVM)
4 challenges
Managing Real Infrastructure
4 challenges
Mandatory Access Control
4 challenges
Memory & the OOM Killer
5 challenges
Merging
3 challenges
Multi-Container Apps with Compose
4 challenges
Name Resolution on the Host
4 challenges
Navigating the Filesystem
7 challenges
netfilter & iptables Fundamentals
4 challenges
Network Troubleshooting
3 challenges
Networking
1 challenges
Networking & Configuration
4 challenges
Networking Basics
8 challenges
nftables -- the Modern Firewall
4 challenges
Operating Containers
4 challenges
Orchestration & Strategy
3 challenges
Orientation -- Databases on Linux
3 challenges
Orientation -- The Administrator's Mindset
2 challenges
Orientation -- The Diagnostic Mindset
3 challenges
Orientation -- The Security Mindset
2 challenges
Orientation -- Why Compliance and Auditing
2 challenges
Orientation -- Why Configuration Management
2 challenges
Orientation -- Why Containers
3 challenges
Orientation -- Why Cryptography and PKI
3 challenges
Orientation -- Why Host Networking
2 challenges
Orientation -- Why Networks Matter
3 challenges
Orientation -- Why Version Control
2 challenges
Package & Dependency Problems
4 challenges
Package & Software Management
4 challenges
Performance & Tuning
4 challenges
Performance Bottlenecks
4 challenges
Permission & Authentication Problems
5 challenges
Permissions & Ownership
6 challenges
Permissions & Security
2 challenges
Pipes, Redirection & Shell Scripting
8 challenges
PKI & Certificate Authorities
4 challenges
Playbooks
3 challenges
Process & Resource Control
4 challenges
Processes & Services
9 challenges
Querying Data
5 challenges
RAID & Advanced Filesystems
4 challenges
Reading and Writing Files
9 challenges
Rebasing
4 challenges
Recording Changes
4 challenges
Remediation
4 challenges
Remotes & Collaboration
5 challenges
Reporting & Evidence
4 challenges
Roles & Reuse
5 challenges
Routing
5 challenges
Routing on Linux
3 challenges
Scheduling Tasks
4 challenges
Schema & Constraints
4 challenges
Secrets with Ansible Vault
3 challenges
Secure Remote Access with SSH
2 challenges
Seeing the Traffic
5 challenges
Service & systemd Failures
5 challenges
Service Administration
4 challenges
SQL Foundations from the CLI
4 challenges
SSH Keys & Authentication
4 challenges
Stateful Filtering & NAT
5 challenges
Storage & Disk Management
6 challenges
Storage & Disks
2 challenges
Storage Fundamentals
5 challenges
Subnetting
6 challenges
Symmetric Encryption
4 challenges
System & Service Hardening
4 challenges
systemd & Service Management
4 challenges
Tags & Releases
4 challenges
Templates & Files
5 challenges
Text Processing
1 challenges
The Audit Subsystem at Scale
5 challenges
The Boot Process
4 challenges
The Diagnostic Toolkit
5 challenges
The Frameworks
3 challenges
The Layered Model
3 challenges
The Linux Network Stack
3 challenges
The Linux Primitives Behind Containers
3 challenges
The Physical and Link Layer
5 challenges
The Repository
3 challenges
The Transport Layer
5 challenges
Time, Localization & Environment
4 challenges
TLS and the Handshake
3 challenges
Troubleshooting
13 challenges
Undoing Things
5 challenges
Users & Groups
1 challenges
Users & Groups Administration
7 challenges
Users, Authentication & PAM
3 challenges
Users, Groups & Identity
5 challenges
Users, Roles & Permissions
4 challenges
Variables, Facts & Registers
5 challenges
VPN with WireGuard
3 challenges
Vulnerability & Patch Management
4 challenges
Welcome to Linux
5 challenges
COURSES
Structured Learning Paths
Start from zero and progress through curated courses with hands-on challenges at every step.
terminal
Beginner
Linux Fundamentals
The flagship course of Terminal 43. Takes a complete beginner from "what is Linux?" to...
72 challenges
15950 pts
~55h
code
Coming Soon
Shell Scripting Mastery
Take your Linux skills to the next level. Master shell scripting from basic variable assignment...
Intermediate
~30h
SIMULATIONS
Cyber City
Defend your infrastructure against waves of cyber attacks. Deploy firewalls, CDNs, and caches to keep your servers alive. A visual, real-time approach to learning cybersecurity concepts.
- Deploy defenses in real-time against simulated attacks
- Play solo or host multiplayer sessions with your team
- Multiple districts to explore and defend
Cyber City // Defense Dashboard
WAVE 3/5
UPTIME: 94%
Firewall
3
DDoS
!
CDN
2
● SQL Injection detected on /api/users
● Firewall blocked 1,247 malicious requests
ECOSYSTEM
Part of the Terminal43 Universe
Your progress here connects to a cross-platform ecosystem. One account, one journey.
T43 SYSTEM YOU ARE HERE
System Mastery
SSH into Linux containers. Solve challenges. Master the command line hands-on.
712 challenges
T43 CTF
Capture The Flag
Exploit real vulnerabilities. Reverse binaries. Pwn boxes. Competitive cybersecurity.
ctf.terminal43.ro →BLOCKSARENA
Visual Coding
Learn to code by building games. Block-based programming that bridges to real code.
blocksarena.com →T43 CODE
Code Challenges
Master programming through hands-on coding challenges with instant feedback.
code.terminal43.ro →