Common error resolution: How do I fix ``Error: Already running on PID 1234``?
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If you're seeing this error::

    Error: Already running on PID 1234 (or pid file '/tmp/gunicorn--dsmr_webinterface.pid' is stale)

Just delete the PID file and restart the webinterface::

    sudo rm /tmp/gunicorn--dsmr_webinterface.pid
    sudo supervisorctl restart dsmr_webinterface