Rails服务器运行报错：UsuariosController#login触发SystemStackError(stack level too deep)

Hey Diego, sorry you're stuck with this frustrating error—especially since the app runs smooth in production. Let's break down how to track down that infinite recursion causing the SystemStackError.

First, target the callback root cause (error hits in callbacks.rb) #

Stack level too deep almost always means an infinite recursive loop, and since the error lands in ActiveSupport's callbacks, start here:

• Check controller callbacks: Look at your UsuariosController for before_action, after_action, or around_action hooks tied to the login action. Is there a hook that calls login itself, or triggers another method that circles back to login? For example:

  before_action :login, only: [:login] # This creates an infinite loop!
  

• Check Datamapper model callbacks: If your login logic interacts with a Usuario model, inspect any model-level callbacks (like before_save, after_find, or custom hooks). Could a model callback trigger a controller method that then calls back to the model? For example, an after_find hook that calls an authentication method, which reloads the user, triggering after_find again.

Next, verify "identical" environments aren't hiding subtle differences #

Even if you think everything matches, Ubuntu 16.04 vs. your production server's OS might introduce hidden mismatches:

• Match Ruby patch versions exactly: You're using ruby-1.9.3-p448 on the new server—what patch version runs in production? Small Ruby patches can fix (or introduce) callback-related bugs. Use RVM to switch to the exact same patch:

  rvm install 1.9.3-pXXX # Replace XXX with your production patch number
  rvm use 1.9.3-pXXX@your_app_gemset --default
  bundle install
  

• Cross-check gem versions: Run bundle list on both servers and compare line-by-line. Even with an identical Gemfile.lock, transitive dependencies can sometimes install differently. Pay extra attention to:
  • activesupport (obviously, since the error is here)
  • Datamapper-related gems (dm-rails, dm-core, dm-validations)
  • Rack and ActionPack versions
• Check environment variables: Ensure your new server's RAILS_ENV is set correctly (matches production). If using Passenger with Nginx, verify the rails_env directive in your Nginx config points to production.

Get the full stack trace to pinpoint the loop #

The error log you shared only shows the final crash point—we need the full recursive call chain to see what's looping:

• Temporarily enable local debugging: Edit config/environments/production.rb and set:

  config.consider_all_requests_local = true
  

  Restart your server, visit /usuarios/login, and you'll get a detailed stack trace showing exactly which methods are calling each other repeatedly. Don't forget to set this back to false after debugging to avoid exposing sensitive app details.
• Run in development mode (if possible): If you can spin up a dev server on the new box with rails s, the error will spit out a full stack trace directly in the terminal, which is easier to parse.

Bonus checks for edge cases #

• Session storage misconfiguration: If your production server uses a remote session store (like Memcached) and the new server doesn't have access, could fallback logic trigger a loop? Verify your config/initializers/session_store.rb matches production.
• File permission issues: Rare, but incorrect permissions on config files or tmp directories can cause unexpected callback behavior. Ensure tmp/cache and tmp/sessions are writable by the web server user.

Once you spot the recursive loop in the full stack trace, fixing it should be straightforward—usually just removing a circular callback or adjusting a method call that's triggering itself.

内容的提问来源于stack exchange，提问作者Diego Muñoz