Web application could not be started

Please install the mysql adapter: `gem install activerecord-mysql-adapter` (mysql is not part of the bundle. Add it to Gemfile.) (LoadError)
  /var/lib/gems/1.9.1/gems/bundler-1.3.5/lib/bundler/rubygems_integration.rb:214:in `block in replace_gem'
  /var/lib/gems/1.9.1/gems/activerecord-3.2.12/lib/active_record/connection_adapters/mysql_adapter.rb:5:in `'
  /var/lib/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
  /var/lib/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `block in require'
  /var/lib/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:236:in `load_dependency'
  /var/lib/gems/1.9.1/gems/activesupport-3.2.12/lib/active_support/dependencies.rb:251:in `require'
  /var/lib/gems/1.9.1/gems/activerecord-

sed -i 's/adapter: mysql/adapter: mysql2/g' /var/www/redmine/config/database.yml

/etc/init.d/apache2 restart