Redmine

I have a working install of 5.1.0, but I now need to access the API, from the server where Redmine is installed.

To do this, I'm stopping Apache, and then directly starting Passenger as 'passenger start'. I'm then trying to get a page with cURL:

 $ curl http://127.0.0.1:3000/

This doesn't return the front page - the 'passenger start' output just says "//public/index.html is not found". Redmine is installed at /opt/redmine-5.1.0, so I've also tried:

 $ curl http://127.0.0.1:3000/opt/redmine-5.1.0
 $ curl http://127.0.0.1:3000/opt/redmine-5.1.0/
 $ curl http://127.0.0.1:3000/opt/redmine-5.1.0/public/

But these don't work either, returning

"//public/opt/redmine-5.1.0" failed (2: No such file or directory)
"//public/opt/redmine-5.1.0/index.html" is not found (2: No such file or directory)
"//public/opt/redmine-5.1.0/public/index.html" is not found (2: No such file or directory)

Can anyone tell me what URL I should use to get, for example, the admin user's details? Where does the '//public' come from?