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solutions.md

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+# Practice Exam Solutions
+
+## Task 1: Company Portal Unreachable
+
+### Diagnosis
+
+```bash
+# Check nginx status
+sudo systemctl status nginx
+
+# Test nginx configuration
+sudo nginx -t
+# Output: nginx: [emerg] unexpected "}" in /etc/nginx/sites-enabled/company.local:8
+
+# View the config file
+cat /etc/nginx/sites-available/company.local
+```
+
+### Problem
+The nginx configuration file for company.local has a **missing semicolon** after `index index.html`.
+
+### Solution
+
+```bash
+# Edit the configuration file
+sudo nano /etc/nginx/sites-available/company.local
+
+# Find this line:
+    index index.html
+
+# Change to (add semicolon):
+    index index.html;
+
+# Test configuration
+sudo nginx -t
+# Output: nginx: configuration file /etc/nginx/nginx.conf syntax is ok
+
+# Reload nginx
+sudo systemctl reload nginx
+```
+
+### Verification
+```bash
+curl http://company.local
+# Should return HTML with "Company Portal"
+```
+
+---
+
+## Task 2: Online Shop Shows 403 Forbidden
+
+### Diagnosis
+
+```bash
+# Check nginx error log
+sudo tail /var/log/nginx/shop_error.log
+# Output: open() "/var/www/shop/index.html" failed (13: Permission denied)
+
+# Check file permissions
+ls -la /var/www/shop/
+# Output: ---------- 1 www-data www-data ... index.html
+# (No permissions at all!)
+```
+
+### Problem
+The index.html file has **wrong permissions** (chmod 000 - no read/write/execute for anyone).
+
+### Solution
+
+```bash
+# Fix the file permissions
+sudo chmod 644 /var/www/shop/index.html
+
+# Verify permissions (should show -rw-r--r--)
+ls -la /var/www/shop/index.html
+```
+
+### Verification
+```bash
+curl http://shop.local
+# Should return HTML with "Online Shop"
+```
+
+---
+
+## Task 3: API Returns 502 Bad Gateway
+
+### Diagnosis
+
+```bash
+# Check nginx error log for API
+sudo tail /var/log/nginx/api_error.log
+# Output: connect() to unix:/var/run/php/php8.x-fpm.sock failed (2: No such file or directory)
+
+# Check PHP-FPM status
+sudo systemctl status php*-fpm
+# Output: Active: inactive (dead)
+```
+
+### Problem
+The **PHP-FPM service is stopped and disabled**. Nginx cannot forward PHP requests.
+
+### Solution
+
+```bash
+# Find the PHP-FPM version
+php -v
+# or: ls /etc/php/
+
+# Start PHP-FPM (replace 8.3 with your version if different)
+sudo systemctl start php8.3-fpm
+
+# Enable to start on boot
+sudo systemctl enable php8.3-fpm
+
+# Verify it's running
+sudo systemctl status php8.3-fpm
+# Should show: Active: active (running)
+```
+
+### Verification
+```bash
+curl http://api.local:8080
+# Should return JSON with "status": "success"
+```
+
+---
+
+## Task 4: Docker Application Unreachable
+
+### Diagnosis
+
+```bash
+# Check if Docker container is running
+sudo docker ps
+# Output: practice-webapp is running (HEALTHY)
+
+# Check if port is listening
+sudo ss -tulnp | grep 8888
+# Output: Shows docker-proxy listening on 8888
+
+# Check firewall status
+sudo ufw status
+# Output: 8888/tcp DENY Anywhere
+```
+
+### Problem
+The **firewall (UFW) is blocking port 8888**. The Docker container is running correctly, but connections are denied.
+
+### Solution
+
+```bash
+# Remove the deny rule
+sudo ufw delete deny 8888/tcp
+
+# Allow port 8888
+sudo ufw allow 8888/tcp
+
+# Verify firewall rules
+sudo ufw status
+# Should show: 8888/tcp ALLOW Anywhere
+```
+
+### Verification
+```bash
+curl http://localhost:8888
+# Should return HTML with "Docker Application"
+```
+
+---
+
+## Task 5: Database Connection Refused
+
+### Diagnosis
+
+```bash
+# Try to connect with the user
+mysql -u webuser -p'WebPass123!' practicedb
+# Output: ERROR 1045 (28000): Access denied for user 'webuser'@'localhost'
+
+# Check which users exist (as root)
+sudo mysql -e "SELECT user, host FROM mysql.user WHERE user='webuser';"
+# Output: webuser | 10.0.0.1
+# (User is bound to wrong IP, not localhost!)
+```
+
+### Problem
+The MySQL user `webuser` is bound to **wrong host IP** (10.0.0.1 instead of localhost).
+
+### Solution
+
+```bash
+# Connect as root
+sudo mysql
+
+# Create user for localhost (or recreate)
+DROP USER IF EXISTS 'webuser'@'10.0.0.1';
+CREATE USER 'webuser'@'localhost' IDENTIFIED BY 'WebPass123!';
+GRANT ALL PRIVILEGES ON practicedb.* TO 'webuser'@'localhost';
+FLUSH PRIVILEGES;
+EXIT;
+```
+
+Or as a one-liner:
+```bash
+sudo mysql -e "DROP USER IF EXISTS 'webuser'@'10.0.0.1'; CREATE USER 'webuser'@'localhost' IDENTIFIED BY 'WebPass123!'; GRANT ALL PRIVILEGES ON practicedb.* TO 'webuser'@'localhost'; FLUSH PRIVILEGES;"
+```
+
+### Verification
+```bash
+mysql -u webuser -p'WebPass123!' practicedb -e "SELECT * FROM products;"
+# Should show table with products (Laptop, Mouse, Keyboard, Monitor)
+```
+
+---
+
+## Quick Reference: Problem Summary
+
+| Task | Service | Problem | Key Fix |
+|------|---------|---------|---------|
+| 1 | company.local | Missing semicolon in nginx config | Add `;` after `index index.html` |
+| 2 | shop.local | Wrong file permissions (000) | `chmod 644 /var/www/shop/index.html` |
+| 3 | api.local | PHP-FPM service stopped | `systemctl start php*-fpm` |
+| 4 | localhost:8888 | Firewall blocking port | `ufw allow 8888/tcp` |
+| 5 | MySQL | User bound to wrong host | Create user for `'webuser'@'localhost'` |
+
+---
+
+## Diagnostic Approach
+
+For each problem, follow this systematic approach:
+
+1. **Check the symptom** - What error do you see?
+   - Connection refused → Service not running or firewall
+   - 403 Forbidden → Permissions issue
+   - 502 Bad Gateway → Backend service (PHP-FPM) down
+   - Connection timeout → Firewall blocking
+
+2. **Check service status** - Is the service running?
+   ```bash
+   systemctl status nginx
+   systemctl status php*-fpm
+   docker ps
+   ```
+
+3. **Check logs** - What do the logs say?
+   ```bash
+   journalctl -u nginx
+   tail /var/log/nginx/error.log
+   ```
+
+4. **Check configuration** - Is the config valid?
+   ```bash
+   nginx -t
+   cat /etc/nginx/sites-available/...
+   ```
+
+5. **Check permissions** - Can the service read the files?
+   ```bash
+   ls -la /var/www/...
+   ```
+
+6. **Check network** - Is the port accessible?
+   ```bash
+   ss -tulnp
+   ufw status
+   ```
+
+---
+
+*Practice Exam Solutions - Betriebssysteme und Netzwerke*