D4 / SECURITY LABSSTART HERE / 001
FREE LABS // START WITH LINUX

LEARN THE
SYSTEM.
DEFEND IT.

Use a Linux VM you control. Check what's listening, see which services are running and read the firewall rules before changing anything.

START THE FIRST LAB EXPLORE TRAINING
PRACTICE ON YOUR OWN VM.
01/03LINUX / NETWORKS / DETECTION
// THE MISSION 001

FIND WHAT'S
LISTENING.
THEN ASK WHY.

When you find a listening port, identify the process behind it. Read the firewall rules and decide who should be able to reach it. Lab 001 has the commands.

01 LISTENING PORTS
02 RUNNING SERVICES
03 FIREWALL RULES

// CHOOSE YOUR ENTRY POINT

THREE WAYS IN.

The Linux baseline lab is ready. Network Defense and Threat Detection are being written.

01/03
LAB 001 AVAILABLE

LINUX
HARDENING.

Inspect open ports, running services and firewall rules on a test VM.

LINUXSYSTEMDFIREWALLS
02/03
IN DEVELOPMENT

NETWORK
DEFENSE.

Read packet captures, check DNS answers and trace routes when a connection fails.

TCP/IPDNSTRAFFIC ANALYSIS
03/03
IN DEVELOPMENT

THREAT
DETECTION.

Read authentication logs, investigate failed sign-ins and work through alerts.

LOGSINVESTIGATIONDETECTION

FIELD LAB // 001

OPEN A
TERMINAL.

Before you change the configuration, find out which services your Linux VM exposes.

01
USE A LAB VM.

These commands are for a Linux system you own or have permission to administer.

02
CHECK THE BASELINE.

List listening ports, running services and the rules that filter incoming traffic.

03
DECIDE WHAT STAYS.

Check whether each listening service is necessary and who should reach it.

FIELD LAB 001 / LINUX BASELINE● COPY / RUN
student@d4-lab:~$
sudo ss -tulpn
# WHAT THIS SHOWS

Lists TCP and UDP sockets and their processes. Entries bound to 0.0.0.0 or :: listen on all local interfaces. Firewall rules determine who can reach them.

SAFE / READ-ONLY INSPECTION
COPY A COMMAND, THEN RUN IT ON YOUR OWN VM.LAB 001 / FREE
// OUR RULES 004

NO PAYWALLS.
NO FAKE BADGES.
JUST SKILL.

D4 Cyber Academy is an independent online training project. Lessons are free. We're not an accredited school and don't issue academic qualifications.

TRY LAB 001