[ruby-on-rails] Uninitialized constant ActiveSupport::Dependencies::Mutex (NameError)

I'm posting my solution for the other sleep-deprived souls out there:

If you're using RVM, double-check that you're in the correct folder, using the correct ruby version and gemset. I had an array of terminal tabs open, and one of them was in a different directory. typing "rails console" produced the error because my default rails distro is 2.3.x.

I noticed the error on my part, cd'd to the correct directory, and my .rvmrc file did the rest.

RVM is not like Git. In git, changing branches in one shell changes it everywhere. It's literally rewriting the files in question. RVM, on the other hand, is just setting shell variables, and must be set for each new shell you open.

In case you're not familiar with .rvmrc, you can put a file with that name in any directory, and rvm will pick it up and use the version/gemset specified therein, whenever you change to that directory. Here's a sample .rvmrc file:

rvm use 1.9.2@turtles

This will switch to the latest version of ruby 1.9.2 in your RVM collection, using the gemset "turtles". Now you can open up a hundred tabs in Terminal (as I end up doing) and never worry about the ruby version it's pointing to.

Examples related to ruby-on-rails

Embed ruby within URL : Middleman Blog Titlecase all entries into a form_for text field Where do I put a single filter that filters methods in two controllers in Rails Empty brackets '[]' appearing when using .where How to integrate Dart into a Rails app Rails 2.3.4 Persisting Model on Validation Failure How to fix "Your Ruby version is 2.3.0, but your Gemfile specified 2.2.5" while server starting Is the server running on host "localhost" (::1) and accepting TCP/IP connections on port 5432? Rails: Can't verify CSRF token authenticity when making a POST request Uncaught ReferenceError: React is not defined

Examples related to rubygems

You don't have write permissions for the /Library/Ruby/Gems/2.3.0 directory. (mac user) find_spec_for_exe': can't find gem bundler (>= 0.a) (Gem::GemNotFoundException) How to fix "Your Ruby version is 2.3.0, but your Gemfile specified 2.2.5" while server starting You don't have write permissions for the /var/lib/gems/2.3.0 directory Can't install gems on OS X "El Capitan" How to avoid "cannot load such file -- utils/popen" from homebrew on OSX How can I set a proxy server for gem? How to install CocoaPods? Error while installing json gem 'mkmf.rb can't find header files for ruby' How to downgrade or install an older version of Cocoapods

Examples related to compatibility

Which TensorFlow and CUDA version combinations are compatible? IE11 Document mode defaults to IE7. How to reset? Internet Explorer 11 disable "display intranet sites in compatibility view" via meta tag not working Possible to restore a backup of SQL Server 2014 on SQL Server 2012? How to set IE11 Document mode to edge as default? Is it possible to run a .NET 4.5 app on XP? I want to get Year, Month, Day, etc from Java Date to compare with Gregorian Calendar date in Java. Is this possible? Fragments onResume from back stack Uninitialized constant ActiveSupport::Dependencies::Mutex (NameError) How to run multiple Python versions on Windows