The following cap commands are available now, but I am unable to start unicorn using unicorn:start.
cap -vT
cap bundle:install # Install the current Bundler environment.
cap deploy # Deploys your project.
cap deploy:assets:clean # Run the asset clean rake task.
cap deploy:assets:clean_expired # Clean up any assets that haven't been...
cap deploy:assets:precompile # Run the asset precompilation rake task.
cap deploy:assets:rollback # to shared/assets/manifest.yml, and fi...
cap deploy:assets:symlink # [internal] This task will set up a sy...
cap deploy:assets:update_asset_mtimes # [internal] Updates the mtimes for ass...
cap deploy:check # Test deployment dependencies.
cap deploy:cleanup # Clean up old releases.
cap deploy:cold # Deploys and starts a `cold' application.
cap deploy:create_symlink # Updates the symlink to the most recen...
cap deploy:finalize_update # [internal] Touches up the released code.
cap deploy:migrate # Run the migrate rake task.
cap deploy:migrations # Deploy and run pending migrations.
cap deploy:pending # Displays the commits since your last ...
cap deploy:pending:diff # Displays the `diff' since your last d...
cap deploy:restart # Blank task exists as a hook into whic...
cap deploy:rollback # Rolls back to a previous version and ...
cap deploy:rollback:cleanup # [internal] Removes the most recently ...
cap deploy:rollback:code # Rolls back to the previously deployed...
cap deploy:rollback:revision # [internal] Points the current symlink...
cap deploy:setup # Prepares one or more servers for depl...
cap deploy:start # Blank task exists as a hook into whic...
cap deploy:stop # Blank task exists as a hook into whic...
cap deploy:symlink # Deprecated API.
cap deploy:update # Copies your project and updates the s...
cap deploy:update_code # Copies your project to the remote ser...
cap deploy:upload # Copy files to the currently deployed ...
cap development # Set the target stage to `development'.
cap invoke # Invoke a single command on the remote...
cap multistage:ensure # [internal] Ensure that a stage has be...
cap multistage:prepare # Stub out the staging config files.
cap production # Set the target stage to `production'.
cap rvm:create_gemset # Create gemset
cap rvm:install_gem # Install a gem, 'cap rvm:install_gem G...
cap rvm:install_ruby # Install RVM ruby to the server, creat...
cap rvm:install_rvm # Install RVM of the given choice to th...
cap rvm:uninstall_gem # Uninstall a gem, 'cap rvm:uninstall_g...
cap shell # Begin an interactive Capistrano session.
cap staging # Set the target stage to `staging'.
Extended help may be available for these tasks.
Type `cap -e taskname' to view it.
Following gems are available
gem list --local | grep cap
capistrano (2.14.1)
capistrano-ext (1.2.1)
capistrano-unicorn (0.1.6)
rvm-capistrano (1.2.7)
It seems that you haven't required it in your deploy.rb.
require 'capistrano-unicorn'