How do you log server errors on django sites

Django Sentry is a good way to go, as already mentioned, but there is a bit of work involved in setting it up properly (as a separate website). If you just want to log everything to a simple text file here's the logging configuration to put in your settings.py

LOGGING = {
    'version': 1,
    'disable_existing_loggers': False,
    'handlers': {
        # Include the default Django email handler for errors
        # This is what you'd get without configuring logging at all.
        'mail_admins': {
            'class': 'django.utils.log.AdminEmailHandler',
            'level': 'ERROR',
             # But the emails are plain text by default - HTML is nicer
            'include_html': True,
        },
        # Log to a text file that can be rotated by logrotate
        'logfile': {
            'class': 'logging.handlers.WatchedFileHandler',
            'filename': '/var/log/django/myapp.log'
        },
    },
    'loggers': {
        # Again, default Django configuration to email unhandled exceptions
        'django.request': {
            'handlers': ['mail_admins'],
            'level': 'ERROR',
            'propagate': True,
        },
        # Might as well log any errors anywhere else in Django
        'django': {
            'handlers': ['logfile'],
            'level': 'ERROR',
            'propagate': False,
        },
        # Your own app - this assumes all your logger names start with "myapp."
        'myapp': {
            'handlers': ['logfile'],
            'level': 'WARNING', # Or maybe INFO or DEBUG
            'propagate': False
        },
    },
}

django-db-log, mentioned in another answer, has been replaced with:

https://github.com/dcramer/django-sentry

Well, when DEBUG = False, Django will automatically mail a full traceback of any error to each person listed in the ADMINS setting, which gets you notifications pretty much for free. If you'd like more fine-grained control, you can write and add to your settings a middleware class which defines a method named process_exception(), which will have access to the exception that was raised:

http://docs.djangoproject.com/en/dev/topics/http/middleware/#process-exception

Your process_exception() method can then perform whatever type of logging you'd like: writing to console, writing to a file, etc., etc.

Edit: though it's a bit less useful, you can also listen for the got_request_exception signal, which will be sent whenever an exception is encountered during request processing:

http://docs.djangoproject.com/en/dev/ref/signals/#got-request-exception

This does not give you access to the exception object, however, so the middleware method is much easier to work with.