** [192.168.0.50 :: err] Host key verification failed.
** [192.168.0.50 :: err] fatal: The remote end hung up unexpectedly

Solution
You would need to login to your staging server (as your deployment user) and do an initial checkout for one time for the ssh keys to work.
So you could do something like the following:

$ ssh user_name@staging_server
$sh -c 'git clone -q git_user@192.168.0.50:repo_name /some/tmp/dir/temp_repo_name

Make sure that you reply ‘y’ to the question about the authenticity of the host as in:
The authenticity of host '192.168.0.50 (192.168.0.50)' can't be established.
RSA key fingerprint is xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:xxb.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.0.50' (RSA) to the list of known hosts.

Net delete the newly created git project from your tmp directory, and then you should be able to use cap deploy as normal again from your development pc

Solution
Install the capistrano_colours gem that can be found here.
sudo gem install capistrano_colors

Solution

• Change your Gemfile to replace
  gem 'rails', '3.0.3'
  with
  gem 'rails', '3.0.4'
• Run:
  bundle update rails
• Remove the old gems by using:
  git status
  and then
  git rm name_of_3.0.3_gem
• Add the new gems to your git
  git add vendor/cache
• Check in to your repository the new files
  git commit vendor/cache -m 'upgrade to rails 3.0.4'
• Make sure that you also check in both your Gemfile and Gemfile.lock into your git repository
  git commit Gemfile Gemfile.lock -m 'update Gemfiles to use 3.0.4'
  otherwise when you try to deploy you will see the error:
  You have modified your Gemfile in development but did not check the resulting snapshot (Gemfile.lock) into version control
• push everything to your git repository:
  git push
• Deploy your application with capistrano as usual:
  cap deploy
• Your new gems for 3.0.4 should be installed on the share/bundle folder

500 Internal Server Error

Solution
Thanks to a blog post from Brendon Wilson here, the last missing piece from the puzzle in order to have your application running is to add the following line to the top of your deploy.rb file:

require 'bundler/capistrano'

and redo your cap deploy.

Thanks Brendon.

bundle command not found
or
Enter your password to install the bundled RubyGems to your system:

Solution
You may be able to see in your deploy.rb file a commented section that says the following:

As Capistrano executes in a non-interactive mode and therefore doesn’t cause
any of your shell profile scripts to be run ….

So in order for capistrano to be able to find your bundle command you should add in your deploy.rb file a line with your paths (ie):

default_environment['PATH']='/usr/lib/ruby/gems/1.8/bin:/home/your_name/.gems/bin:/usr/local/bin:/usr/bin:/bin'

If you have the previous line your bundle command can run, but if you try to do cap:deploy your bundler will probably give you an error as it would ask for your sudo password. In order to avoid this error and to make it work you have to add another line with your gem path (ie):

default_environment['GEM_PATH']='/home/your_name/.gems:/usr/lib/ruby/gems/1.8'

making sure that your home directory path for your gems is first in the list.

Solution
As the server was moved you would need to copy your ssh public key from the deployment server to the new server again for the password-less logins to work again.
Follow the details here how to copy your public key across, login in once with your password, and after that your capistrano recipe should be working again as normal.

Solution
Set your :repository as a file in your host as in:
set :repository, "file:///home/username/git_on_server/projects/repo_name.git"

Then also set up your local_repository, as in:
set :local_repository, "user_name@server_domain_name:/home/username/git_on_server/projects/repo_name.git"

RubyGem version error: rack(0.3.0 not ~> 1.0.0)

Solution
Log in with ssh to your dreamhost account and then install the newer version of rack that is not yet installed in dreamhost:

gem install rack

That assumes that you have followed the instructions for setting up your local gems in dreamhost (here) and you already have a ~/username/.gems directory.

You may probably need to also add the following to your config/environment.rb :

ENV['GEM_PATH'] = ‘/home/USERNAME/.gems’

Note 09-Sep-2009
It seems that according to the dreamhost wiki we need to add the following to the config/environment.rb, instead of the line above:

if ENV['RAILS_ENV'] == ‘production’
ENV['GEM_PATH'] = ‘/home/USERNAME/.gems’
require ‘/home/USERNAME/.gems/gems/rack-1.0.0/lib/rack.rb’
end

to use the locally installed rack-1.0.0 gem, instead of the rack installed by dreamhost.

Solution
On your local development pc freeze the rails:

rake rails:freeze:gems

Add the new code to your svn repository:

svn commit -m 'freeze rails'

And then deploy to dreamhost using capistrano:

cap deploy

Your rails project located on dreamhost should be frozen to your current Rails version.

Solution

1. First change the environment.rb file to use the rails version in your deployment server

   RAILS_GEM_VERSION = '2.0.2' unless defined? RAILS_GEM_VERSION
   

2. You should probably be geting the error: undefined method = time zone by now, so make sure you comment out from further down your environment.rb file the line:

   config.time_zone = 'UTC'

3. Some further errors would be caused by the file config/initializers/new_rails_defaults.rb, so make sure you comment out the following lines:

   ActiveRecord::Base.include_root_in_json = true
   ActiveRecord::Base.store_full_sti_class = true
   ActiveSupport.use_standard_json_time_format = true
   ActiveSupport.use_standard_json_time_format = true

You should be able to deploy and use your application now.