title: gunicorn not found on heroku
body: <p>I want to deploy a very basic Django app on Heroku. I followed the instructions, but the browser shows me the Heroku error page and the heroku logs say</p>
  
  <pre><code>bash: gunicorn: command not found
  </code></pre>
  
  <p>I have gunicorn in my requirements.txt and configured the wsgi.py and Procfile as instructed by the documentation. What else can I try?</p>
  
  <p>Edit: I also tried to install gunicorn manually on Heroku (<code>heroku run pip install gunicorn</code>), which worked fine, so I am pretty sure that gunicorn is installed. Why doesn't Heroku find it?</p>
  
  <p>Edit 2: It seems that I can install gunicorn manually (<code>heroku run bash</code> and then <code>pip install gunicorn</code>:</p>
  
  <pre><code>~ $ gunicorn
  usage: gunicorn [OPTIONS] [APP_MODULE]
  gunicorn: error: No application module specified.
  </code></pre>
  
  <p>but when i log out and log in to the bash again, i get:</p>
  
  <pre><code>~ $ gunicorn
  bash: gunicorn: command not found
  </code></pre>
  
  <p>Heroku seems to install but then discard gunicorn. How can that be?</p>