LFCS 3 🐧 Setting Up a Practice Lab — Options
The LFCS is a performance-based exam. You cannot pass it by reading. The tasks require you to sit at a terminal and perform actions on a live system: create users, configure services, manage storage, troubleshoot networks. A practice lab is not optional—it is the mechanism by which the knowledge becomes skill. This chapter covers the options for building one, from a simple virtual machine on your laptop to a full network simulation, and the exam simulator that comes with the exam purchase.
Key point: Every LFCS candidate should have a Linux virtual machine they can break and rebuild. The exam includes two free sessions of the killer.sh exam simulator, which provides 20–25 tasks in an environment that mirrors the real exam. The lab and the simulator serve different purposes: the lab is for daily practice, and the simulator is for exam rehearsal.
Why a practice lab matters
The performance problem. The LFCS is graded by a script that inspects the state of the system. A user that is created but has the wrong UID fails. A mount that is not in /etc/fstab fails. The only way to learn what “correct” means is to perform the task, verify the state, and repeat until it is automatic. Reading about lvcreate is not the same as running it, seeing the output, and checking lvs afterward.
The reset problem. Practice involves mistakes. A bad fstab entry can prevent the system from booting. A misconfigured firewall can lock you out. A partition table mistake can destroy data. A virtual machine can be snapshotted and restored, so mistakes are cheap. On a physical system, they are not.
The distribution problem. The exam is distribution-independent, but the commands differ between Ubuntu and CentOS. A practice lab lets you use the distribution you are most comfortable with, or both. The tasks generalize, but the syntax does not always.
The network problem. Some tasks involve networking: static routing, bridge and bonding devices, firewalls, reverse proxies. A single VM can handle most of these, but some tasks benefit from a second VM or a simulated network. The practice lab can scale from one machine to several as needed .
a. Virtual machine on your laptop
The simplest lab is a single Linux virtual machine running on your computer. It provides root access, a terminal, and the ability to snapshot and restore.
The recommended configuration from a study plan for the LFCS is a virtual machine with 2 CPUs, 4 GB of RAM, and a 40 GB disk, plus two or three additional virtual disks of 5–10 GB each for storage practice . The additional disks are necessary for LVM, partitioning, and filesystem tasks. A snapshot taken immediately after installation provides a clean baseline that can be restored whenever the system is broken.
VirtualBox and VMware are the common hypervisors. VirtualBox is free and runs on Windows, macOS, and Linux. The installation process is straightforward: download the hypervisor, download an Ubuntu Server ISO, create a virtual machine, and install the operating system .
Ubuntu Server is a good choice because it is widely used and the exam supports Ubuntu. CentOS Stream is the alternative if you prefer the Red Hat family. The choice should match the distribution you plan to use on the exam, or you can use both to practice the differences.
The advantages of a single VM are simplicity and low resource requirements. It runs on a laptop with 8 GB of RAM. It can be snapshotted before each practice session and restored afterward, so the environment is always clean. The disadvantage is that network simulations are limited to what a single machine can do with virtual interfaces.
b. Multi-VM and network simulation labs
Some tasks require more than one machine. A reverse proxy, a load balancer, or a static routing configuration is easier to practice with two or three VMs connected through a virtual network. GNS3 is a network simulation platform that supports Linux VMs alongside its routing and switching emulation.
A GNS3 lab for the LFCS has been published on GitHub. It requires a host with GNS3 and QEMU installed, 8 GB of RAM minimum, and 40 GB of disk space . The project is available in portable format, with or without the qcow disk images. The lab includes questions and solutions, so it can be used as a self-contained practice environment .
The advantage of a multi-VM lab is realism. Networking tasks that involve two hosts, a firewall, and a router are practiced in an environment that resembles the task. The disadvantage is resource requirements and setup complexity. A laptop with 16 GB of RAM can run two or three VMs; a machine with 8 GB can run one comfortably.
The choice between a single VM and a multi-VM lab depends on the tasks you find most difficult. If storage and user management are the weak areas, a single VM is sufficient. If networking is the weak area, a multi-VM lab is worth the setup cost.
c. The killer.sh exam simulator
The LFCS exam purchase includes two free sessions of the killer.sh exam simulator . The simulator is not a perfect replica of the exam environment, but it provides tasks of the same type and detailed solutions . The simulation includes 20–25 questions, and the results are graded .
The simulator sessions are time-limited. Each session lasts 36 continuous hours from the moment it is activated. The timer is time-based, not usage-based, so activating a session and not using it wastes the access .
The simulator serves a different purpose than the practice lab. The lab is for daily practice and repetition. The simulator is for exam rehearsal: performing tasks under time pressure, in an environment that resembles the exam, with the knowledge that the results are graded. It should be used after the domains have been studied and the lab practice has been completed.
A candidate who passed the LFCS described using both KodeKloud and KillerCoda (the simulator’s companion practice environment) alongside a home lab. The combination of structured labs, free scenarios, and personal practice gave confidence in solving problems quickly and under time constraints .
Complete Example Session
# ============================================
# PART 1: SINGLE VM LAB CONFIGURATION
# ============================================
Hypervisor: VirtualBox or VMware
OS: Ubuntu Server or CentOS Stream
CPU: 2
RAM: 4 GB
Disk 1: 40 GB (system)
Disk 2: 10 GB (storage practice)
Disk 3: 10 GB (storage practice)
Snapshot: Clean baseline after install
SSH: Enabled for easy access
# ============================================
# PART 2: MULTI-VM LAB (GNS3)
# ============================================
Host: Linux with GNS3 + QEMU
CPU: Multicore (i5/Ryzen 5)
RAM: 8 GB minimum
Disk: 40 GB available
Project: LFCS-GNS3-Portable
Includes: Questions and solutions
# ============================================
# PART 3: KILLER.SH SIMULATOR ACCESS
# ============================================
Included: With LFCS exam purchase
Sessions: 2 free
Duration: 36 hours per session
Format: 20-25 graded tasks
Access: Training portal → Exam Checklist
→ Preparing for the Exam
→ Exam Simulator button
# ============================================
# PART 4: DAILY PRACTICE ROUTINE
# ============================================
90 minutes: Hands-on practice in VM
30 minutes: Review commands and concepts
30 minutes: Practice questions
Daily: Snapshot before, restore after
# ============================================
# PART 5: STORAGE PRACTICE SETUP
# ============================================
Add 2-3 virtual disks (5-10 GB each)
Practice: fdisk, parted, pvcreate, vgcreate
lvcreate, mkfs, mount, fstab
lvextend, resize2fs, swap
# ============================================
# PART 6: NETWORKING PRACTICE SETUP
# ============================================
Single VM: Static IP, firewall, SSH, routing
Multi-VM: Reverse proxy, load balancer,
bridge, bonding, NAT
# ============================================
# PART 7: SERVICE PRACTICE
# ============================================
Create custom systemd units
Practice: systemctl enable, start, status
journalctl -u
Troubleshooting failed services
# ============================================
# PART 8: USER PRACTICE
# ============================================
useradd, usermod, userdel
chage, passwd
sudo configuration
ACLs, resource limits
# ============================================
# PART 9: SIMULATOR USAGE
# ============================================
Use after domains are studied
Perform tasks under time pressure
Review graded results
Identify weak domains
Return to lab for targeted practice
# ============================================
# PART 10: LAB HYGIENE
# ============================================
Take a snapshot before each session
Restore after practice
Keep a notes file for commands
Test persistence: reboot and verify
Break things deliberately and fix themThe ten parts summarized the single VM configuration, the multi-VM lab, the simulator access, the daily routine, storage and networking practice, service and user practice, simulator usage, and lab hygiene.
Quick Reference
Lab Options
| Option | Requirements | Best For |
|---|---|---|
| Single VM | 8 GB RAM, VirtualBox | Daily practice, most tasks |
| Multi-VM (GNS3) | 8 GB+ RAM, GNS3 + QEMU | Networking, reverse proxy |
| Killer.sh | Exam purchase | Exam rehearsal |
| KodeKloud labs | Subscription | Structured practice |
Single VM Configuration
| Component | Recommendation |
|---|---|
| Hypervisor | VirtualBox (free) or VMware |
| OS | Ubuntu Server or CentOS Stream |
| CPU | 2 |
| RAM | 4 GB |
| System disk | 40 GB |
| Extra disks | 2–3 × 5–10 GB |
| Snapshot | Clean baseline |
Simulator Details
| Item | Value |
|---|---|
| Provider | killer.sh |
| Sessions | 2 free with exam |
| Duration | 36 hours per session |
| Tasks | 20–25 |
| Grading | Yes |
| Access | Training portal → Exam Checklist |
Practice Resources
| Resource | Type |
|---|---|
| killer.sh | Exam simulator |
| KodeKloud | Interactive labs |
| KillerCoda | Free scenarios |
| LFCS practice tool | 83+ Docker scenarios |
| GNS3 LFCS lab | Network simulation |
Best Practices
✅ Do This:
# Snapshot before every session
Restore the clean baseline after practice # ✅
# Add extra virtual disks for storage practice
2-3 disks of 5-10 GB each # ✅
# Practice persistence
Reboot after configuring and verify the change survives # ✅
# Use the simulator after studying
Save the killer.sh sessions for exam rehearsal # ✅
# Practice daily
90 minutes of hands-on practice # ✅
# Test fstab entries with mount -a
Before rebooting # ✅
# Keep notes of commands and pitfalls
A personal cheat sheet # ✅❌ Don’t Do This:
# Don't practice on your production system
Use a VM # ❌
# Don't skip the extra disks
Storage tasks need unpartitioned disks # ❌
# Don't activate the simulator too early
The 36-hour timer starts immediately # ❌
# Don't forget to restore the snapshot
A broken VM is not a practice environment # ❌
# Don't rely on a single VM for networking tasks
Some tasks need two machines # ⚠️
# Don't practice without verifying
The grader checks state, not effort # ❌
# Don't memorize without practicing
The exam is performance-based # ❌Common Pitfalls
| Pitfall | Why It Happens | Fix |
|---|---|---|
| No extra disks | Only system disk | Add 2–3 virtual disks |
| Broken system | Bad fstab or firewall | Snapshot and restore |
| Simulator timer wasted | Activated too early | Save for exam rehearsal |
| Networking tasks fail | Single VM limitation | Set up second VM |
| Forgot to verify | Rushed practice | Check state after each task |
| No persistence testing | Only tested in session | Reboot and verify |
| Resource exhaustion | Too many VMs on laptop | Use one VM or cloud |
Real-World Examples
1. Single VM Setup
VirtualBox → New VM
Type: Linux
Version: Ubuntu (64-bit)
RAM: 4096 MB
Disk: 40 GB VDI
Add disks: 2 × 10 GB2. GNS3 Lab
Host: Linux + GNS3 + QEMU
RAM: 8 GB minimum
Disk: 40 GB
Project: LFCS-GNS3-Portable
Includes: Questions and solutions3. Simulator Access
1. Log in to trainingportal.linuxfoundation.org
2. Click Start/Resume for LFCS
3. Go to Preparing for the Exam
4. Click Exam Simulator button
5. Redirected to killer.sh
6. 2 sessions, 36 hours each4. Storage Practice
# Add disks, then:
fdisk /dev/sdb
pvcreate /dev/sdb1
vgcreate myvg /dev/sdb1
lvcreate -L 5G -n mylv myvg
mkfs.ext4 /dev/myvg/mylv
mkdir /mnt/data
mount /dev/myvg/mylv /mnt/data5. Persistence Test
echo '/dev/myvg/mylv /mnt/data ext4 defaults 0 0' >> /etc/fstab
mount -a
reboot
df -h /mnt/data6. Service Practice
cat > /etc/systemd/system/myapp.service << EOF
[Unit]
Description=My App
[Service]
ExecStart=/usr/local/bin/myapp
Restart=always
[Install]
WantedBy=multi-user.target
EOF
systemctl daemon-reload
systemctl enable --now myapp7. Firewall Practice
# Ubuntu
ufw allow 80/tcp
ufw status
# CentOS
firewall-cmd --add-port=80/tcp --permanent
firewall-cmd --reload8. User Practice
useradd -m -s /bin/bash -u 1500 alice
usermod -aG developers alice
chage -M 90 alice
id alice9. Networking Practice
# Static IP (Ubuntu netplan)
cat > /etc/netplan/01-static.yaml << EOF
network:
version: 2
ethernets:
ens33:
addresses: [192.168.1.100/24]
gateway4: 192.168.1.1
nameservers:
addresses: [8.8.8.8]
EOF
netplan apply10. Simulator Rehearsal
Activate killer.sh session
Set a 2-hour timer
Complete as many tasks as possible
Review graded results
Identify weak domains
Return to lab for targeted practiceVisual
Lab Hierarchy
┌─────────────────────────────────────────────────────────────┐
│ PRACTICE LAB OPTIONS │
│ │
│ ┌─────────────────────────────────────────────────────┐ │
│ │ SINGLE VM │ │
│ │ 2 CPU, 4 GB RAM, 40 GB + 2×10 GB disks │ │
│ │ VirtualBox / VMware │ │
│ │ Best for: daily practice, most tasks │ │
│ └─────────────────────────────────────────────────────┘ │
│ │
│ ┌─────────────────────────────────────────────────────┐ │
│ │ MULTI-VM (GNS3) │ │
│ │ 8 GB+ RAM, GNS3 + QEMU │ │
│ │ Best for: networking, reverse proxy │ │
│ └─────────────────────────────────────────────────────┘ │
│ │
│ ┌─────────────────────────────────────────────────────┐ │
│ │ KILLER.SH SIMULATOR │ │
│ │ Included with exam, 2 sessions, 36 hours each │ │
│ │ Best for: exam rehearsal │ │
│ └─────────────────────────────────────────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────┘Daily Practice Cycle
┌─────────────────────────────────────────────────────────────┐
│ SNAPSHOT (clean baseline) │
│ │ │
│ ▼ │
│ PRACTICE (90 min hands-on) │
│ │ │
│ ▼ │
│ VERIFY (check state) │
│ │ │
│ ▼ │
│ REVIEW (30 min commands) │
│ │ │
│ ▼ │
│ RESTORE (snapshot) │
│ │ │
│ ▼ │
│ NEXT SESSION │
│ │
│ Snapshot before, restore after. Mistakes are free. │
│ │
└─────────────────────────────────────────────────────────────┘Simulator Access Flow
┌─────────────────────────────────────────────────────────────┐
│ trainingportal.linuxfoundation.org │
│ │ │
│ ▼ │
│ Start / Resume LFCS exam │
│ │ │
│ ▼ │
│ Exam Checklist │
│ │ │
│ ▼ │
│ Preparing for the Exam section │
│ │ │
│ ▼ │
│ Exam Simulator button │
│ │ │
│ ▼ │
│ killer.sh (auto-logged in) │
│ │ │
│ ▼ │
│ 2 sessions × 36 hours │
│ │
│ Activate only when ready. Timer is continuous. │
│ │
└─────────────────────────────────────────────────────────────┘Resource Requirements
┌─────────────────────────────────────────────────────────────┐
│ SINGLE VM MULTI-VM │
│ │
│ CPU: 2 cores CPU: Multicore │
│ RAM: 4 GB RAM: 8 GB minimum │
│ Disk: 40 + 20 GB Disk: 40 GB │
│ Hypervisor: VirtualBox GNS3 + QEMU │
│ │
│ Runs on a laptop with 8 GB Needs a stronger machine │
│ │
└─────────────────────────────────────────────────────────────┘Summary
| Option | Requirements | Purpose |
|---|---|---|
| Single VM | 8 GB RAM, VirtualBox | Daily practice |
| Multi-VM (GNS3) | 8 GB+ RAM, GNS3 + QEMU | Networking practice |
| killer.sh | Exam purchase | Exam rehearsal |
| KodeKloud | Subscription | Structured labs |
| KillerCoda | Free | Scenario practice |
| Item | Value |
|---|---|
| Recommended VM | 2 CPU, 4 GB RAM, 40 GB + extra disks |
| Extra disks | 2–3 × 5–10 GB |
| Snapshot | Before every session |
| Simulator sessions | 2 free, 36 hours each |
| Simulator tasks | 20–25 |
| Practice routine | 90 min hands-on daily |
Key takeaways:
- A practice lab is not optional. The LFCS is performance-based. You learn the tasks by performing them, verifying the state, and repeating until the commands are automatic.
- A single virtual machine is the minimum. It should have 2 CPUs, 4 GB of RAM, and a 40 GB system disk, plus two or three additional virtual disks for storage practice. A snapshot taken after installation provides a clean baseline for restoration .
- Extra virtual disks are necessary for storage tasks. LVM, partitioning, and filesystem exercises require unpartitioned disks. Without them, the storage domain cannot be practiced.
- A multi-VM lab is useful for networking. GNS3 supports Linux VMs alongside its network emulation. A published LFCS lab provides questions and solutions, but it requires 8 GB of RAM and a host with GNS3 and QEMU installed .
- The killer.sh simulator is included with the exam. It provides 2 sessions of 36 hours each, with 20–25 graded tasks. It should be used for exam rehearsal, not for initial learning .
- Snapshot before every practice session. Mistakes are part of learning, but they are only cheap if the environment can be restored. A broken fstab entry or a misconfigured firewall can prevent the system from booting.
- Practice persistence. Many tasks require changes that survive a reboot. After configuring a mount, a service, or a firewall rule, reboot and verify. The grader checks the state after reboot.
Remember: The LFCS is a practical exam, and practical skill comes from practice. A virtual machine on your laptop, snapshotted and restored, is sufficient for most of the domains. A multi-VM lab adds realism for networking tasks. The killer.sh simulator, included with the exam purchase, is the closest thing to the real exam and should be saved for rehearsal. The lab is where you learn; the simulator is where you test. Both are necessary, and neither is a substitute for the other. Set up the lab, practice daily, and use the simulator when the domains are covered. The commands will become automatic, and the exam will feel like another day in the terminal .
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