Using these steps you can install Redmine on Debian 8 using MySQL as database backend, nginx as web server and Unicorn as application server. Redmine will be installed at /srv/redmine/ path.

Debian 8 is the first version of Debian that is using systemd, all other steps are the same also for older versions of Debian.

Add user account that will be used for redmine application.

useradd -m -s /bin/bash redmine

Install required packages

apt-get install curl git

curl -sSL https://rvm.io/mpapis.asc | gpg --import -
curl -Lk https://get.rvm.io | bash -s stable
source /etc/profile.d/rvm.sh # adds rvm to path (instead of re-logging)
cd /tmp
git clone https://github.com/skaes/rvm-patchsets
cd /tmp/rvm-patchsets
bash install.sh
bash -lc '/usr/local/rvm/bin/rvm install ruby-2.1.5'
bash -lc 'rvm use --default 2.1.5'

As a database will be used MySQL server.

apt-get install mysql-server

Then create dedicated user account

mysql -p

CREATE DATABASE redmine CHARACTER SET utf8;
CREATE USER 'redmine'@'localhost' IDENTIFIED BY 'Your-Secret-Password';
GRANT ALL PRIVILEGES ON redmine.* TO 'redmine'@'localhost';

mkdir /srv/redmine/
mkdir /srv/redmine/run/
cd /srv/redmine/
wget http://www.redmine.org/releases/redmine-3.1.0.tar.gz
tar zxvf redmine-3.1.0.tar.gz
mv redmine-3.1.0 wwwroot
rm redmine-3.1.0.tar.gz

cd /srv/redmine/wwwroot/config/
cp configuration.yml.example configuration.yml
cp database.yml.example database.yml

now edit database.yml file and change MySQL connection:

production:
  adapter: mysql2
  database: redmine
  host: localhost
  username: redmine
  password: "Your-Secret-Password"
  encoding: utf8

Install dependencies:

apt-get install make gcc libxml2-dev libxslt-dev libmysql++-dev libmysqlclient-dev libmagickcore-dev libmagickwand-dev libpq-dev imagemagick ruby-dev

cd /srv/redmine/wwwroot
bash -lc 'rvm 2.1.5 do gem install bundler'
bash -lc 'cd /srv/redmine/wwwroot; RAILS_ENV=production rvm 2.1.5 do bundle install --without development test'

Now make sure that redmine user can access Redmine files.

chown -R redmine:redmine /srv/redmine/

And following commands should be executed as redmine user.

su - redmine # login as redmine user
bash -lc 'cd /srv/redmine/wwwroot; RAILS_ENV=production rvm 2.1.5 do bundle exec rake generate_secret_token'
bash -lc 'cd /srv/redmine/wwwroot; RAILS_ENV=production rvm 2.1.5 do bundle exec rake db:migrate'
bash -lc 'cd /srv/redmine/wwwroot; RAILS_ENV=production rvm 2.1.5 do bundle exec rake redmine:load_default_data REDMINE_LANG=en'
exit # logout

To enable log rotation create file /etc/logrotate.d/redmine using this:

echo <<EOF > /etc/logrotate.d/redmine
/srv/redmine/wwwroot/log/*.log
{
    rotate 14
    daily
    compress
    delaycompress
    copytruncate
}
EOF

Install unicorn server.

bash -lc 'rvm 2.1.5 do gem install unicorn'

mkdir /etc/unicorn

Add systemd init file /lib/systemd/system/unicorn.service:

cat <<EOF > /lib/systemd/system/unicorn.service
[Unit]
Description=Unicorn

[Service]
Type=simple
User=redmine
WorkingDirectory=/srv/redmine/wwwroot
Environment=RAILS_ENV=production
PIDFile=/srv/redmine/run/unicorn.pid
ExecStart=/bin/bash -lc 'rvm 2.1.5 do unicorn -D -c /etc/unicorn/redmine.rb -E production'

[Install]
WantedBy=multi-user.target

EOF

and unicorn config file /etc/unicorn/redmine.rb:

cat <<'EOF' > /etc/unicorn/redmine.rb
   
worker_processes 4
stderr_path '/srv/redmine/wwwroot/log/stderr.log'
stdout_path '/srv/redmine/wwwroot/log/stdout.log'

listen '/srv/redmine/run/unicorn.sock'
pid "/srv/redmine/run/unicorn.pid"

timeout 300
preload_app true

before_fork do |server, worker|
    Signal.trap 'TERM' do
        puts 'Unicorn master intercepting TERM and sending myself QUIT instead'
    Process.kill 'QUIT', Process.pid
end

defined?(ActiveRecord::Base) and
    ActiveRecord::Base.connection.disconnect!
end

after_fork do |server, worker|
    Signal.trap 'TERM' do
        puts 'Unicorn worker intercepting TERM and doing nothing. Wait for master to send QUIT'
end

defined?(ActiveRecord::Base) and
    ActiveRecord::Base.establish_connection
end
EOF

Install server:

apt-get install nginx

Add upstream configuration for Unicorn (/etc/nginx/conf.d/unicorn.conf):

cat <<EOF > /etc/nginx/conf.d/unicorn.conf
upstream unicorn {
  server     unix:/srv/redmine/run/unicorn.sock  fail_timeout=10s;
}
EOF

Redmine site configuration /etc/nginx/sites-available/redmine using hostname my-redmine.company.com

cat <<'EOF' > /etc/nginx/sites-available/redmine
server {
  listen *:80;
  server_name           my-redmine.company.com;

  index  index.html index.htm;

  access_log            /var/log/nginx/redmine.access.log combined;
  error_log             /var/log/nginx/redmine.error.log;

  location / {
    proxy_pass            http://unicorn;
    proxy_read_timeout    90;
    proxy_connect_timeout 90;
    proxy_redirect        off;

    proxy_set_header      X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header      Host $http_host;
  }
}
EOF

and activate the site:

ln -s /etc/nginx/sites-available/redmine /etc/nginx/sites-enabled/

systemctl start unicorn.service

systemctl reload nginx.service

To access newly installed instance open web browser and access it using hostnamed configured in nginx.

During installation was created default administrator with these credentials: