OperationalError: could not connect to database

OperationalError: could not connect to database

$ python manage.py migrate
Traceback (most recent call last):
  ...
OperationalError: could not connect to server: Connection refused

Why this happens

DB not running, wrong host/port, or firewall blocking connection.

Fix

Start DB, verify credentials in settings.DATABASES, and network reachability.

Wrong code

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'db', 'USER': 'u', 'PASSWORD': 'p', 'HOST': 'localhost', 'PORT': '9999'
    }
}

Fixed code

DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.postgresql',
        'NAME': 'db', 'USER': 'u', 'PASSWORD': 'p', 'HOST': '127.0.0.1', 'PORT': '5432'
    }
}
# Ensure PostgreSQL is running