rails capistrano having problems with rake db:migrate - ruby-on-rails

Question

I just ran rake db:migrate directly on my server with no problems:
$ pwd
/var/www/vhosts/example.com/current
$ rake db:migrate
Then i tried to run it via a capistrano task and i get an error. The task and output are below. Why does rake db:migrate not work via my capistrano task?
task
namespace :deploy do
# run the db migrations
task :run_migrations, :roles => :db do
puts "RUNNING DB MIGRATIONS"
run "cd #{current_path}; rake db:migrate RAILS_ENV=#{rails_env}"
end
end
cap deploy:run_migrations
$ cap deploy:run_migrations
* executing `deploy:run_migrations'
RUNNING DB MIGRATIONS
* executing "cd /var/www/vhosts/example.com/current; rake db:migrate"
servers: ["example.com"]
[example.com] executing command
** [out :: example.com] (in /var/www/vhosts/example.com/releases/20121122011144)
** [out :: example.com] rake aborted!
** [out :: example.com] no such file to load -- rubygems
** [out :: example.com] /var/www/vhosts/example.com/releases/20121122011144/Rakefile:5:in `require'
** [out :: example.com] (See full trace by running task with --trace)
command finished in 390ms
failed: "sh -c 'cd /var/www/vhosts/example.com/current; rake db:migrate'" on example.com
EDIT
$ ruby -v
ruby 1.9.3p125 (2012-02-16 revision 34643) [x86_64-linux]
$ which ruby
/usr/local/rvm/rubies/ruby-1.9.3-p125/bin/ruby
$ which rails
/usr/local/rvm/gems/ruby-1.9.3-p125/bin/rails
EDIT
When i added --trace to the db migrations, it looks like it's using /usr/lib/ruby/site_ruby/1.8/rake.rb, but from the looks of this:
$ which rake
/usr/local/rvm/gems/ruby-1.9.3-p125/bin/rake
i would have expected it to use rake at /usr/local/rvm/gems/ruby-1.9.3-p125/bin/rake rather than /usr/lib/ruby/site_ruby/1.8/rake.rb.
cap deploy's output from the deploy:run_migrations task
* executing `deploy:run_migrations'
RUNNING DB MIGRATIONS
* executing "cd /var/www/vhosts/example.com/current; rake db:migrate RAILS_ENV=production --trace"
servers: ["example.com"]
[example.com] executing command
** [out :: example.com] (in /var/www/vhosts/example.com/releases/20121123184358)
** [out :: example.com] rake aborted!
** [out :: example.com] no such file to load -- rubygems
** [out :: example.com] /var/www/vhosts/example.com/releases/20121123184358/config/boot.rb:1:in `require'
** [out :: example.com] /var/www/vhosts/example.com/releases/20121123184358/config/boot.rb:1
** [out :: example.com] /var/www/vhosts/example.com/releases/20121123184358/config/application.rb:1:in `require'
** [out :: example.com] /var/www/vhosts/example.com/releases/20121123184358/config/application.rb:1
** [out :: example.com] /var/www/vhosts/example.com/releases/20121123184358/Rakefile:5:in `require'
** [out :: example.com] /var/www/vhosts/famnfo.com/releases/20121123184358/Rakefile:5
** [out :: example.com] /usr/lib/ruby/site_ruby/1.8/rake.rb:1828:in `load'
** [out :: example.com] /usr/lib/ruby/site_ruby/1.8/rake.rb:1828:in `load_rakefile'
** [out :: example.com] /usr/lib/ruby/site_ruby/1.8/rake.rb:1900:in `run'
** [out :: example.com] /usr/bin/rake:8
command finished in 422ms
failed: "sh -c 'cd /var/www/vhosts/example.com/current; rake db:migrate RAILS_ENV=production --trace'" on example.com
EDIT
output after adding #Super Engineers code
* executing `bundle:install'
* executing "ls -x /var/www/vhosts/example.com/releases"
servers: ["example.com"]
[example.com] executing command
command finished in 572ms
* executing "cd /var/www/vhosts/example.com/releases/20121124160218 && bundle install --gemfile /var/www/vhosts/example.com/releases/20121124160218/Gemfile --path /var/www/vhosts/example.com/shared/bundle --deployment --quiet --without development test"
servers: ["example.com"]
[example.com] executing command
** [out :: example.com] You are trying to install in deployment mode after changing
** [out :: example.com] your Gemfile. Run `bundle install` elsewhere and add the
** [out :: example.com] updated Gemfile.lock to version control.
** [out :: example.com]
** [out :: example.com] You have added to the Gemfile:
** [out :: example.com] * mysql2
** [out :: example.com] * therubyracer
** [out :: example.com] * rvm-capistrano
** [out :: example.com] * passenger
** [out :: example.com]
** [out :: example.com] You have deleted from the Gemfile:
** [out :: example.com] * mysql
command finished in 999ms
*** [deploy:update_code] rolling back
* executing "rm -rf /var/www/vhosts/example.com/releases/20121124160218; true"
servers: ["example.com"]
[example.com] executing command
command finished in 826ms
failed: "rvm_path=/usr/local/rvm /usr/local/rvm/bin/rvm-shell 'ruby-1.9.3-p125' -c 'cd /var/www/vhosts/example.com/releases/20121124160218 && bundle install --gemfile /var/www/vhosts/example.com/releases/20121124160218/Gemfile --path /var/www/vhosts/example.com/shared/bundle --deployment --quiet --without development test'" on example.com
EDIT
Entire deploy.rb file
require 'bundler/capistrano'
require 'rvm/capistrano'
# set environment
set :rails_env, "production"
# set the ruby version
set :rvm_ruby_string, 'ruby-1.9.3-p125'
set :rvm_type, 'webadmin'
# server username and password
set :user, 'super'
set :password, 'secret'
# subversion repo username and password
set :scm, :subversion
set :scm_username, "super"
set :scm_password, 'secret'
set :svnserver, "myreposerver"
set :repository, "myrepo"
# project info
set :server, ''
set :application, "FamNFo"
set :applicationdir, '/Volumes/Macintosh HD/Users/myname/Sites/example'
role :web, "example.com"
role :app, "example.com"
role :db, "example.com", :primary => true
set :use_sudo, true
# database config
#set :migrate_env, "#{rails_env}"
# specify the rvm type. We just want to use the system wide one since we're not currently specifying gemsets for each project
set :rvm_type, :system
# where to put the files
set :deploy_to, "/var/www/vhosts/example.com"
# fixes the "sorry, you must have a tty to run sudo" issue
default_run_options[:pty] = true
# precompiles the assets
load 'deploy/assets'
# If you are using Passenger mod_rails uncomment this:
namespace :deploy do
# restart the server
task :restart, :roles => :app do
run "/etc/init.d/http restart graceful"
end
# chmod the files
task :after_update_code, :roles => [:web, :db, :app] do
run "chmod 755 #{release_path}/public -R"
end
# install new gems
desc "run bundle install and ensure all gem requirements are met"
task :install do
run "cd #{current_path} && bundle install --without=test --no-update-sources --trace"
end
# run the db migrations
task :run_migrations, :roles => :db do
puts "RUNNING DB MIGRATIONS"
run "cd #{current_path}; rake db:migrate RAILS_ENV=#{rails_env} --trace"
end
# precompile assets
task :precompile_assets do
run "cd #{release_path}; bundle exec rake assets:precompile RAILS_ENV=#{rails_env}"
end
task :start do ; end
task :stop do ; end
# restart the server
task :restart, :roles => :app, :except => { :no_release => true } do
run "#{sudo} /etc/init.d/httpd restart graceful"
end
end
# hook to run db migrations after code update
after("deploy:update", "deploy:run_migrations")
#after("deploy:update", "deploy:precompile_assets")
after "deploy:update", "deploy:install"
# if you want to clean up old releases on each deploy uncomment this:
after "deploy:restart", "deploy:cleanup" # leave the last 5 releases only

Answer 1

Its because of ruby conflict. I've faced same error. You will need to use rvm/capistrano gem. I'll paste some code from my cap file which will give you some idea about how to set the ruby version while deploying.
install the gem
gem install rvm-capistrano
in you deploy.rb file add these lines
require 'bundler/capistrano'
require 'rvm/capistrano'
set :rvm_ruby_string, "ruby-1.9.3-p125"
set :rvm_type, 'webadmin'
For more information you can visit this link rvm/capistrano

Answer 2

The relevant error here seems to be no such file to load -- rubygems.
Quite likely it is because of multiple ruby installations on the production server.
Check out this previous solution for a similar problem : https://stackoverflow.com/a/2896596/429758
Also, this thread on the capistrano mailing list is helpful: https://groups.google.com/forum/?fromgroups=#!topic/capistrano/JzVPRbQclY4

Answer 3

Are you using rvm/capistrano? With that you can specify the ruby version that you want to use on the server in your capistrano recipes. I suspect that when you run capistrano it's not using your rvm setup, when you login and run the rake task, your user is setup to use the rvm ruby version.