Back to DocsQuick diagnosis
First, identify the type of error:
| Error | Meaning |
|---|---|
ERR_CONNECTION_REFUSED | Web server not listening on the port |
ERR_CONNECTION_TIMED_OUT | Firewall blocks the port or server not responding |
502 Bad Gateway | Nginx can't communicate with PHP-FPM or backend |
503 Service Unavailable | Service is down or overloaded |
504 Gateway Timeout | Backend (PHP, app) taking too long to respond |
403 Forbidden | Wrong file permissions or Nginx/Apache configuration |
404 Not Found | File not found or path configuration error |
500 Internal Server Error | Application error (PHP, etc.) |
1. Is the web server running?
# For Nginx
systemctl status nginx
# For Apache
systemctl status apache2
# If it's down, start it
systemctl start nginx
If it won't start, see the guide: Service that Won't Start
2. Does firewall allow HTTP/HTTPS ports?
ufw status
Ports 80 and 443 must be open:
ufw allow http
ufw allow https
ufw reload
3. Is the web server listening on the right port?
ss -tlnp | grep -E ':80|:443'
If you see no output, Nginx/Apache is not listening on those ports. Check the configuration.
Error 502 Bad Gateway (Nginx + PHP-FPM)
502 indicates Nginx can't communicate with PHP-FPM.
# Verify PHP-FPM is running
systemctl status php8.2-fpm
# If it's down
systemctl start php8.2-fpm
# Check Nginx error log
tail -20 /var/log/nginx/error.log
Verify the .sock file in Nginx configuration matches the real one:
# See available sock
ls /run/php/
# Must match what's in configuration:
# fastcgi_pass unix:/run/php/php8.2-fpm.sock;
Error 403 Forbidden
Most common cause: wrong file permissions on files or directory.
# Fix permissions
chown -R www-data:www-data /var/www/mysite/
find /var/www/mysite/ -type d -exec chmod 755 {} \;
find /var/www/mysite/ -type f -exec chmod 644 {} \;
Another cause: index.html or index.php missing in site root.
Error 500 Internal Server Error
Check the error logs:
# Nginx
tail -50 /var/log/nginx/error.log
# Apache
tail -50 /var/log/apache2/error.log
# Application log (Laravel)
tail -50 /var/www/mysite/storage/logs/laravel.log
Common causes:
- PHP syntax error
- Missing or misconfigured .env file
- Wrong permissions on app cache or logs
- Missing PHP module
Error 504 Gateway Timeout
Backend taking too long to respond. Increase timeout in Nginx:
# In server or location block
proxy_read_timeout 120s;
fastcgi_read_timeout 120s;
Also increase max_execution_time in PHP:
nano /etc/php/8.2/fpm/php.ini
# max_execution_time = 120
systemctl restart php8.2-fpm
DNS not propagated
If site works with IP but not with domain, could be DNS propagation issue:
# Verify DNS from server
nslookup example.com
# Check on external tools
# https://dnschecker.org
Wait for propagation (up to 48 hours) or verify A record is correct in your DNS panel.
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