rails new hoge
cd hoge
rake about

rake aborted!
Could not find a JavaScript runtime. See https://github.com/sstephenson/execjs for a list of available runtimes.

(See full trace by running task with --trace)

echo "gem 'execjs'" >> Gemfile
echo "gem 'therubyracer'" >> Gemfile
bundle install

rake about

About your application's environment
Ruby version              1.9.2 (x86_64-linux)
RubyGems version          1.8.10
Rack version              1.3
Rails version             3.1.3
JavaScript Runtime        therubyracer (V8)
Active Record version     3.1.3
Action Pack version       3.1.3
Active Resource version   3.1.3
Action Mailer version     3.1.3
Active Support version    3.1.3
Middleware                ActionDispatch::Static, Rack::Lock, #<ActiveSupport::Cache::Strategy::LocalCache::Middleware:0x0000001c986b58>, Rack::Runtime, Rack::MethodOverride, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::RemoteIp, Rack::Sendfile, ActionDispatch::Reloader, ActionDispatch::Callbacks, ActiveRecord::ConnectionAdapters::ConnectionManagement, ActiveRecord::QueryCache, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ParamsParser, ActionDispatch::Head, Rack::ConditionalGet, Rack::ETag, ActionDispatch::BestStandardsSupport
Application root          /home/akira/work/hoge
Environment               development
Database adapter          sqlite3
Database schema version