Review exercises
Table of contents
- Validation quiz
- Exercise 1: User management
- Exercise 2: Permissions
- Mini-project: Configure an application user
- Next steps
1 - Validation quiz
Questions
Q1. Which command adds a user to a group without removing them from other groups?
See the answer
usermod -aG groupe utilisateur
The -a (append) is crucial! Without it, the user is removed from all their existing groups.
Q2. What are the octal permissions for rwxr-xr--?
See the answer
754
- rwx = 4+2+1 = 7
- r-x = 4+0+1 = 5
- r-- = 4+0+0 = 4
Q3. How do you edit the sudoers file securely?
See the answer
visudo or sudo visudo
Visudo checks the syntax before saving, avoiding breaking sudo.
Q4. What is the difference between apt remove and apt purge?
See the answer
apt remove: deletes the package but keeps the configuration filesapt purge: deletes the package AND the configuration files
Q5. How do you kill a process that is not responding?
See the answer
kill -9 PID or kill -SIGKILL PID
Signal 9 (SIGKILL) forces immediate termination.
Q6. How do you enable a service at boot AND launch it immediately?
See the answer
sudo systemctl enable --now service
Q7. How do you make an environment variable permanent for a user?
See the answer
Add export VARIABLE=valeur to ~/.bashrc then run source ~/.bashrc
Q8. How do you redirect stdout AND stderr to the same file?
See the answer
commande > fichier.txt 2>&1 or commande &> fichier.txt
Q9. What is the tee command used for?
See the answer
tee splits the output: it writes to a file AND displays it on screen at the same time.
Q10. How do you view the logs of a systemd service in real time?
See the answer
journalctl -u service -f
Results
| Score | Level |
|---|---|
| 10/10 | Excellent! You are ready for Linux 3 |
| 7-9/10 | Good! Review the points you missed |
| 4-6/10 | Average. Reread the relevant chapters |
| 0-3/10 | Start the Linux 2 course over |
🔝 Back to table of contents
2 - Exercise 1: User management
Goal
Create and configure a user with specific groups.
Instructions
# 1. Créez un groupe "developers"
sudo groupadd developers
# 2. Créez un utilisateur "devuser" avec :
# - Home directory
# - Shell bash
# - Membre du groupe developers
sudo useradd -m -s /bin/bash -G developers devuser
# 3. Définissez un mot de passe
sudo passwd devuser
# 4. Vérifiez la création
id devuser
# Devrait afficher : uid=...(devuser) gid=...(devuser) groups=...(devuser),...(developers)
# 5. Ajoutez devuser au groupe sudo
sudo usermod -aG sudo devuser
# 6. Vérifiez les groupes
groups devuser
# 7. Créez un fichier de test dans son home
sudo -u devuser touch /home/devuser/test.txt
# 8. Vérifiez le propriétaire
ls -la /home/devuser/test.txt
Verification
# L'utilisateur devuser doit :
# - Exister (id devuser ne doit pas afficher d'erreur)
# - Avoir /home/devuser comme home
# - Avoir /bin/bash comme shell
# - Être membre de developers et sudo
Cleanup
sudo userdel -r devuser
sudo groupdel developers
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3 - Exercise 2: Permissions
Goal
Configure permissions for a shared project folder.
Instructions
# 1. Créez un groupe projet
sudo groupadd projet
# 2. Créez un dossier partagé
sudo mkdir /srv/projet
# 3. Changez le propriétaire et groupe
sudo chown root:projet /srv/projet
# 4. Configurez les permissions :
# - Propriétaire : rwx
# - Groupe : rwx
# - Autres : r-x
# + SGID pour que les nouveaux fichiers héritent du groupe
sudo chmod 2775 /srv/projet
# 5. Vérifiez
ls -ld /srv/projet
# drwxrwsr-x 2 root projet ... /srv/projet
# 6. Ajoutez votre utilisateur au groupe
sudo usermod -aG projet $USER
# 7. Reconnectez-vous (ou newgrp projet)
newgrp projet
# 8. Créez un fichier dans le dossier
touch /srv/projet/test.txt
# 9. Vérifiez que le fichier appartient au groupe projet
ls -la /srv/projet/test.txt
Questions
- Why do we use SGID (2)?
- What happens if you forget the SGID?
- Why do others have r-x and not rwx?
Answers
- SGID makes new files inherit the group of the directory
- Without SGID, created files would have the user's primary group
- r-x allows reading and accessing the folder without being able to modify/create
Cleanup
sudo rm -rf /srv/projet
sudo groupdel projet
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4 - Mini-project: Configure an application user
Context
You need to configure a server to deploy a Node.js application. You will create a dedicated user with the correct permissions.
Objectives
- Create a
deployuser without interactive access - Create the folder structure
- Configure the permissions
- Create a simple systemd service
Instructions
# === ÉTAPE 1 : Créer l'utilisateur ===
# Créer l'utilisateur système (sans home standard, sans login)
sudo useradd -r -s /usr/sbin/nologin -d /app deploy
# Créer manuellement le répertoire
sudo mkdir -p /app
sudo chown deploy:deploy /app
# Vérifier
id deploy
ls -ld /app
# === ÉTAPE 2 : Structure de dossiers ===
sudo -u deploy mkdir -p /app/{current,releases,shared}
sudo -u deploy mkdir -p /app/shared/{logs,config}
# Vérifier la structure
ls -la /app
ls -la /app/shared
# === ÉTAPE 3 : Créer une application factice ===
# Créer un script simple
cat << 'EOF' | sudo tee /app/current/app.sh
#!/bin/bash
while true; do
echo "[$(date)] Application running..."
sleep 10
done
EOF
# Rendre exécutable
sudo chmod 755 /app/current/app.sh
sudo chown deploy:deploy /app/current/app.sh
# === ÉTAPE 4 : Créer le service systemd ===
cat << 'EOF' | sudo tee /etc/systemd/system/myapp.service
[Unit]
Description=My Application
After=network.target
[Service]
Type=simple
User=deploy
Group=deploy
WorkingDirectory=/app/current
ExecStart=/bin/bash /app/current/app.sh
Restart=always
RestartSec=5
StandardOutput=append:/app/shared/logs/app.log
StandardError=append:/app/shared/logs/app.log
[Install]
WantedBy=multi-user.target
EOF
# Recharger systemd
sudo systemctl daemon-reload
# === ÉTAPE 5 : Tester ===
# Démarrer le service
sudo systemctl start myapp
# Vérifier l'état
sudo systemctl status myapp
# Voir les logs
tail -f /app/shared/logs/app.log
# Arrêter pour nettoyage (Ctrl+C d'abord)
sudo systemctl stop myapp
Final checks
| Item | Verification command | Expected result |
|---|---|---|
| User | id deploy | Exists, no shell |
| /app folder | ls -ld /app | Owned by deploy |
| Service | systemctl status myapp | Active (running) |
| Logs | ls /app/shared/logs/ | app.log exists |
Cleanup
sudo systemctl stop myapp
sudo systemctl disable myapp
sudo rm /etc/systemd/system/myapp.service
sudo systemctl daemon-reload
sudo rm -rf /app
sudo userdel deploy
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5 - Next steps
Congratulations!
You have completed the Linux 2 - Basic Administration course!
What you have learned
Skills acquired
| Skill | Mastery |
|---|---|
| Manage users and groups | ✅ |
| Configure permissions | ✅ |
| Use sudo securely | ✅ |
| Install and manage packages | ✅ |
| Monitor processes | ✅ |
| Manage systemd services | ✅ |
| Configure environment variables | ✅ |
| Use redirections and pipes | ✅ |
Next step: Linux 3
In the Linux 3 - System and Network course, you will learn:
- Advanced file system
- Storage management (LVM, mounting)
- Network configuration
- SSH and secure connections
- Firewall (UFW, iptables)
- Scheduled tasks (cron)
- Archiving and compression
- Advanced search (find, sed, awk)
Tips for making progress
- Practice on VMs: Break things, fix them, start over
- Administer a real server: A cheap VPS to experiment
- Automate: Write scripts for repetitive tasks
- Read the logs: Get used to journalctl
- Document: Note down what you learn
Command summary
Users and groups
| Command | Usage |
|---|---|
useradd -m -s /bin/bash user | Create a user |
usermod -aG groupe user | Add to a group |
passwd user | Set the password |
id user | User information |
Permissions
| Command | Usage |
|---|---|
chmod 755 fichier | Modify permissions |
chown user:group fichier | Change the owner |
ls -la | View permissions |
Packages
| Command | Usage |
|---|---|
apt update && apt upgrade | Update |
apt install package | Install |
apt remove package | Remove |
Processes and services
| Command | Usage |
|---|---|
ps aux | List processes |
kill -9 PID | Force stop |
systemctl start/stop/status | Manage services |
journalctl -u service -f | Logs in real time |
Redirections
| Syntax | Usage |
|---|---|
> | Redirect stdout (overwrites) |
>> | Redirect stdout (appends) |
2> | Redirect stderr |
| | Pipe |
tee | Split the output |