1. ‘tail -f /development.log’

If you are on OSX, the above is easy.
On Windows, I’d suggest looking at Cygwin and getting tail working. It’s worth it.

a) open terminal.
b) Clear the screen before you reattempt what is broken. (Use Apple + K on OSX)
c) Stop tail right after getting the error (CTRL + C)
d) Look for the first line that is not normal Rails and debug output. See next area.

2. Skip all the fluff and go for Ruby errors. You will learn to see “stacktraces” and errors in Ruby/Rails after a little practice.

They will look something akin to this:

1)An error
2)The file that the error occurred in…
3)the line number/and problem code…
4)A sample of the code at and around the error.
…
5) A bunch of code that was run prior to this happening.

3. Did you recently change the file in question? If so, revert what you did?

4. Use logger.debug to print out something right before the error to see if your code is making it that far.