bind() to 0.0.0.0:80 failed (98: Address already in use) — Port Already in Use

O que causa este erro

Another process (Apache, another Nginx instance, or another service) is already listening on the same port.

Como corrigir

Find the conflicting process with ss -tlnp or netstat -tlnp. Stop the conflicting process or change Nginx's listen port.

# Find process using port 80
sudo lsof -i :80
sudo ss -tlnp | grep :80
# Stop conflicting service
sudo systemctl stop apache2