How can I trace an HTTP 500 error from web brick?

I don’t know what happened. I had been adding some session stuff with
before filters to my base controller classes when suddenly I started
getting error 500 which is internal server error. I commented out all
the before filters I had, rebooted the machine and all that. It
doesn’t even get to the first line of any controller as far as I can
tell. Usually if I just add a puts debug statement someplace it comes
out in the console log, but I’m not having any luck with that.

Look at /log/development.log… assuming you’re in dev mode.