Getting it So Very Wrong in Rails - Foreman, Byebug and Debug

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Last Updated On: 2025-09-01 04:31:52 -0400

Every so often a perfect storm of interrelated circumstances takes you by surprise and causes you to go awry. In my case, I made a few changes to how I develop Rails applications and lost, temporarily, the ability to interactively debug things. Let me explain.

For a very long time, I’ve developer Rails applications simply by running:

bin/rails s -p5000

This runs the Rails server on port 5000 and simply dropping in the statement:

byebug

would launch the Ruby debugger – even in a running controller – and I could debug with great ease.

And then ByeBug was replaced with debug and this and I noticed that I could no longer interactively debug in the same way. Yes I would see the code stop executing and then I would try and enter commands but they never, ever worked.

Finally I threw up my hands and assumed one of three things:

Either I’m stupid and can’t figure it out.
Or there’s something wrong with the debugger and a future patch will fix it.
Or I’m just missing something.

I finally took the time to dig into it again this morning and what I realized was that at the time this started happening for me, I also made the shift to using Foreman:

foreman start -f Procfile.dev

for all my Rails development. And, when I realized that, that gave me the answer:

Foreman was grabbing my input and it was never getting to the debugger!

So this means that if I want to debug interactively, I need to:

Either skip using Foreman (using different tabs to run every part of the build chain)
Write two Foreman scripts, one for everything and one for everything except the rails server

No matter how experienced you are, it is terribly easy to mistake correlation for causation.