5 minute read At Shopify we frequently need to debug production Rails problems. Adding extra debugging code takes time to write and deploy, so we’ve learned how to use tools like gdb and rbtrace to quickly track down these issues. In this post, we’ll explain how to use gdb to retrieve a Ruby call stack, inspect environment variables, and debug a really odd warning message in production. We recently ran into an issue where we were seeing a large number of similar warning messages spamming our log files: /artifacts/ruby/2.1.0/gems/rack-1.6.4/lib/rack/utils.rb:92: warning: regexp match /.../n against to UTF-8 string This means we are trying to match an ASCII regular expression on a UTF-8 source string.