Need a reboot after a deployment with Capistrano - ruby-on-rails

Question

I'm running a rails 3 application hosted on a Ubuntu 12.04 VPS. I'm using Capistrano for the deployment and nginx + unicorn for the server.
My problem is that if I did a "cap deploy", my website displays the old code until I reboot my VPS. I check the current code on the server and it is the right one. I have already tried to restart nginx, but it doesn't work.
My deploy file (I followed the Railscast):
# deploy.rb
require "bundler/capistrano"
require 'new_relic/recipes'
server "188.165.145.167", :web, :app, :db, primary: true
set :application, "neurones"
set :user, "neurones"
set :deploy_to, "/home/neurones/apps/#{application}"
set :deploy_via, :remote_cache
set :use_sudo, false
set :shared_children, shared_children + %w{public/uploads}
set :scm, "git"
set :repository, "git#github.com:khcr/neurones.git"
set :branch, "master"
default_run_options[:pty] = true
ssh_options[:forward_agent] = true
after "deploy", "deploy:cleanup" # keep only the last 5 releases
after "deploy:update", "newrelic:notice_deployment" # update new relic
namespace :deploy do
%w[start stop restart].each do |command|
desc "#{command} unicorn server"
task command, roles: :app, except: {no_release: true} do
run "/etc/init.d/unicorn_#{application} #{command}"
end
end
task :setup_config, roles: :app do
sudo "ln -nfs #{current_path}/config/nginx.conf /etc/nginx/sites-enabled/#{application}"
sudo "ln -nfs #{current_path}/config/unicorn_init.sh /etc/init.d/unicorn_#{application}"
run "mkdir -p #{shared_path}/config"
put File.read("config/database.example.yml"), "#{shared_path}/config/database.yml"
puts "Now edit the config files in #{shared_path}."
end
after "deploy:setup", "deploy:setup_config"
task :symlink_config, roles: :app do
run "ln -nfs #{shared_path}/config/database.yml #{release_path}/config/database.yml"
end
after "deploy:finalize_update", "deploy:symlink_config"
desc "Make sure local git is in sync with remote."
task :check_revision, roles: :web do
unless `git rev-parse HEAD` == `git rev-parse origin/master`
puts "WARNING: HEAD is not the same as origin/master"
puts "Run `git push` to sync changes."
exit
end
end
before "deploy", "deploy:check_revision"
end

Answer 1

I resolved the problem.
Looking in the unicorn log (thanks Domon for the idea), I saw the error:
error reloading config_file=/home/neurones/apps/neurones/current/config/unicorn.rb: Application has been already initialized. (RuntimeError)
I changed unicorn_init.sh from:
restart|reload)
sig HUP && echo reloaded OK && exit 0
echo >&2 "Couldn't reload, starting '$CMD' instead"
run "$CMD"
;;
to
restart|reload)
sig USR2 && echo reloaded OK && exit 0
echo >&2 "Couldn't reload, starting '$CMD' instead"
run "$CMD"
;;