foreman only shows line with “started with pid #” and nothing else

I’ve been able to resolve this issue by 2 different ways:

1. From https://github.com/ddollar/foreman/wiki/Missing-Output:

   If you are not seeing any output from your program, there is a likely
   chance that it is buffering stdout. Ruby buffers stdout by default. To
   disable this behavior, add this code as early as possible in your
   program:

   # ruby
   $stdout.sync = true
   

2. By installing foreman via the heroku toolbelt package

But I still don’t know what’s happening nor why this 2 ways above resolved the issue…