all required packages for

server ~ $ emerge dev-ruby/rubygems

install ruby on rails version required by redmine
H
Install the preferred database /client MySQL/

server ~ $ emerge postgresql

Configure and create the database for redmine

CREATE ROLE redmine LOGIN ENCRYPTED PASSWORD 'my_password' NOINHERIT VALID UNTIL 'infinity';
CREATE DATABASE redmine WITH ENCODING='UTF8' OWNER=redmine;

download and extract redmine

server ~ $ wget http://rubyforge.org/frs/download.php/67144/redmine-0.8.7.tar.gz
server ~ $ tar xvf redmine-0.8.7.tar.gz

Copy config/database.yml.example to config/database.yml

server ~ $ cp redmine-0.8.7/config/database.yml.example redmine-0.8.7/config/database.yml
server ~ $ nano redmine-0.8.7/config/database.yml

and edit this file in order to configure your database settings for your “production” environment

production:
  adapter: postgresql
  database: redmine
  host: localhost
  username: redmine
  password: my_password
  encoding: utf8

make sure to install PosgreSQL adapter for Ruby

server ~ $ gem install postgres-pr

make sure to install rmagick if you wish to export Gantt to png

server ~ $ emerge dev-ruby/rmagick

Generate a session store secret. This is required on the trunk version of Redmine at r2493 or above and the released 0.8.7 version or above.
Redmine stores session data in cookies by default, which requires a secret to be generated. This can be done by running:

server ~ $ cd redmine-0.8.7
server redmine-0.8.7 $ rake config/initializers/session_store.rb

Now we have to populate the database by running the following command

server redmine-0.8.7 $ rake db:migrate RAILS_ENV="production"

now you can load the default configuration data into the database

server redmine-0.8.7 $ rake redmine:load_default_data RAILS_ENV="production"

The and the group who runs Redmine must have write permission on the following subdirectories: files, log, tmp (create the last one if not present).

server redmine-0.8.7 $ mkdir tmp public/plugin_assets
server redmine-0.8.7 $ chown -R user:group files log tmp public/plugin_assets
server redmine-0.8.7 $ chmod -R 775 files log tmp public/plugin_assets

I will continue soon with and init scripts.