The following tasks is what I use for starting  , stopping, restarting and my unicorn server:

 

desc "Start unicorn"
task :start, :except => { :no_release => true } do
  run "cd #{current_path} ; bundle exec unicorn_rails -c config/unicorn.rb -D -E production"
end

desc "Stop unicorn"
task :stop, :except => { :no_release => true } do
  run "kill -s QUIT `cat #{shared_path}/pids/unicorn.pid`"
end

desc "Zero-downtime restart of Unicorn"

task :restart, :except => { :no_release => true } do

run "kill -s USR2 `cat #{shared_path}/pids/unicorn.pid`"

end