Upgrade to Capistrano 3.0 ref: http://qiita.com/katton/items/e5cca6c4f94d140ae2d6

file0.rb

group :development do
  # ...
  gem 'capistrano'
  gem 'capistrano-rails'
  gem 'capistrano-rbenv'
  gem 'capistrano-bundler'
  # ...
end

file1.rb

# Load DSL and Setup Up Stages
require 'capistrano/setup'

# Includes default deployment tasks
require 'capistrano/deploy'

# Includes tasks from other gems included in your Gemfile
#
# For documentation on these, see for example:
#
#   https://github.com/capistrano/rvm
#   https://github.com/capistrano/rbenv
#   https://github.com/capistrano/chruby
#   https://github.com/capistrano/bundler
#   https://github.com/capistrano/rails/tree/master/assets
#   https://github.com/capistrano/rails/tree/master/migrations
#
# require 'capistrano/rvm'
# require 'capistrano/rbenv'
# require 'capistrano/chruby'
# require 'capistrano/bundler'
# require 'capistrano/rails/assets'
# require 'capistrano/rails/migrations'

# Loads custom tasks from `lib/capistrano/tasks' if you have any defined.
Dir.glob('lib/capistrano/tasks/*.cap').each { |r| import r }

file2.rb

# Load DSL and Setup Up Stages
require 'capistrano/setup'

# Includes default deployment tasks
require 'capistrano/deploy'

require 'capistrano/rbenv'

set :rbenv_type, :user # or :system, depends on your rbenv setup
set :rbenv_ruby, '2.0.0-p247'

require 'capistrano/bundler'
require 'capistrano/rails'

# Loads custom tasks from `lib/capistrano/tasks' if you have any defined.
Dir.glob('lib/capistrano/tasks/*.cap').each { |r| import r }

file3.rb

namespace :deploy do

  desc 'Restart application'
  task :restart do
    on roles(:app), in: :sequence, wait: 5 do
      # Your restart mechanism here, for example:
      execute :mkdir, '-p', release_path.join('tmp') # <= これを追加する
      execute :touch, release_path.join('tmp/restart.txt')
    end
  end
  # ...
end