How do I run a rake task from Capistrano?

A little bit more explicit, in your \config\deploy.rb, add outside any task or namespace:

namespace :rake do    desc "Run a task on a remote server."    # run like: cap staging rake:invoke task=a_certain_task    task :invoke do      run("cd #{deploy_to}/current; /usr/bin/env rake #{ENV['task']} RAILS_ENV=#{rails_env}")    end  end

Then, from /rails_root/, you can run:

cap staging rake:invoke task=rebuild_table_abc

Capistrano 3 Generic Version (run any rake task)

Building a generic version of Mirek Rusin's answer:

desc 'Invoke a rake command on the remote server'task :invoke, [:command] => 'deploy:set_rails_env' do |task, args|  on primary(:app) do    within current_path do      with :rails_env => fetch(:rails_env) do        rake args[:command]      end    end  endend

Example usage: cap staging "invoke[db:migrate]"

Note that deploy:set_rails_env requires comes from the capistrano-rails gem

...couple of years later...

Have a look at capistrano's rails plugin, you can see at https://github.com/capistrano/rails/blob/master/lib/capistrano/tasks/migrations.rake#L5-L14 it can look something like:

desc 'Runs rake db:migrate if migrations are set'task :migrate => [:set_rails_env] do  on primary fetch(:migration_role) do    within release_path do      with rails_env: fetch(:rails_env) do        execute :rake, "db:migrate"      end    end  endend