Fix Nginx "Address Already in Use"

Understanding the Error

nginx: [emerg] bind() to 0.0.0.0:80 failed (98: Address already in use)

Another process is using port 80 or 443.

Find What's Using the Port

# Find process
sudo lsof -i :80
sudo lsof -i :443
sudo netstat -tlnp | grep -E ":80|:443"
sudo ss -tlnp | grep -E ":80|:443"

Common Culprits

1. Apache Already Running

sudo systemctl stop apache2
sudo systemctl disable apache2  # Prevent on boot
sudo systemctl start nginx

2. Old Nginx Process

sudo pkill nginx
sudo systemctl start nginx

3. Other Web Servers (Lighttpd, Caddy, Tomcat)

sudo systemctl stop lighttpd
sudo systemctl stop tomcat

4. Docker Container Exposing Port

docker ps
docker stop container_name

Force Kill Process

# Kill by PID
sudo kill -9 PID

# Kill by port
sudo fuser -k 80/tcp
sudo fuser -k 443/tcp

Nginx Already Running But Not Responding

# Check if nginx processes exist
ps aux | grep nginx

# Graceful restart
sudo nginx -s reload

# Full stop and start
sudo nginx -s stop
sudo systemctl start nginx

IPv6 vs IPv4 Conflict

You may have both listening on different addresses:

# Use specific IP instead of all
listen 192.168.1.100:80;
# Instead of
listen 80;

Check for Zombie Processes

ps aux | grep defunct
# Reboot if needed to clear

After killing the conflicting process, Nginx should start normally.