A few common issues are reported when trying to run Dallinger. Always run with the –verbose flag for full logs

Python Processes Kept Alive

Sometimes when trying to run experiments consecutively in Debug mode, a straggling process creates Server 500 errors. These are caused by background python processes and/or gunicorn workers. Filter for them using:

ps -ef | grep -E "python|gunicorn"

This will display all running processes that have the name python or gunicorn. To kill all of them, run these commands:

pkill python
pkill gunicorn

Known Postgres issues

If you get an error like the following…

createuser: could not connect to database postgres: could not connect to server:
    Is the server running locally and accepting
    connections on Unix domain socket "/tmp/.s.PGSQL.5432"?

…then you probably did not start the app.

If you get a fatal error that your ROLE does not exist, run these commands:

createuser dallinger
dropdb dallinger
createdb -O dallinger dallinger

Common Sandbox Error

❯❯ Launching the experiment on MTurk...

❯❯ Error parsing response from /launch, check web dyno logs for details: <!DOCTYPE html>
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <meta charset="utf-8">
        <title>Application Error</title>
        <style media="screen">
          html,body,iframe {
            margin: 0;
            padding: 0;
          html,body {
            height: 100%;
            overflow: hidden;
          iframe {
            width: 100%;
            height: 100%;
            border: 0;
        <iframe src="//"></iframe>
Traceback (most recent call last):
  File "/Users/user/.virtualenvs/dallinger/bin/dallinger", line 11, in <module>
    load_entry_point('dallinger', 'console_scripts', 'dallinger')()
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 697, in main
    rv = self.invoke(ctx)
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/click/", line 535, in invoke
    return callback(*args, **kwargs)
  File "/Users/user/Dallinger/dallinger/", line 558, in sandbox
    _deploy_in_mode(u'sandbox', app, verbose)
  File "/Users/user/Dallinger/dallinger/", line 550, in _deploy_in_mode
    deploy_sandbox_shared_setup(verbose=verbose, app=app)
  File "/Users/user/Dallinger/dallinger/", line 518, in deploy_sandbox_shared_setup
    launch_data = _handle_launch_data('{}/launch'.format(heroku_app.url))
  File "/Users/user/Dallinger/dallinger/", line 386, in _handle_launch_data
    launch_data = launch_request.json()
  File "/Users/user/.virtualenvs/dallinger/lib/python3.6/site-packages/requests/", line 892, in json
    return complexjson.loads(self.text, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/", line 339, in loads
    return _default_decoder.decode(s)
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/", line 364, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/", line 382, in raw_decode
    raise ValueError("No JSON object could be decoded")

If you get this from the sandbox, this usually means there’s a deeper issue that requires dallinger logs –app XXXXXX. Usually this could be a requirements.txt file error (missing dependency or reference to an incorrect branch).