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Zeus preloads your Rails app so that your normal development tasks such as console, server, generate, and specs/tests take less than one second.

This screencast gives a quick overview of how to use zeus with Rails.

Watch the screencast!

More technically speaking, Zeus is a language-agnostic application checkpointer for non-multithreaded applications. Currently only ruby is targeted, but explicit support for other languages is on the horizon.

Requirements (for use with Rails)

  • OS X 10.7+ OR Linux 2.6.13+
  • Rails 3.x
  • Ruby 1.9.3+ with backported GC from Ruby 2.0 OR Rubinius

You can install the GC-patched ruby from this gist for rbenv or this gist for RVM. This is not actually 100% necessary, especially if you have a lot of memory. Feel free to give it a shot first without, but if you're suddenly out of RAM, switching to the GC-patched ruby will fix it.


Install the gem.

gem install zeus

Q: "I should put it in my Gemfile, right?"

A: No. You can, but running bundle exec zeus instead of zeus adds precious seconds to commands that otherwise would be quite a bit faster. Zeus was built to be run from outside of bundler.


Start the server:

zeus start

The server will print a list of available commands.

Run some commands in another shell:

zeus console
zeus server
zeus test test/unit/widget_test.rb
zeus test spec/widget_spec.rb
zeus generate model omg
zeus rake -T
zeus runner omg.rb


To add/modify commands, see docs/ruby/

To get started hacking on Zeus itself, see docs/

See also the handy contribution guide at

Alternative plans

The default plan bundled with zeus only supports Rails 3.x. There is a project (currently WIP) to provide Rails 2.3 support at