Al instalar redmine en Debian 9.2 aparece el error:
Could not find gem 'mysql2 (~> 0.4.0)' in any of the gem sources listed in your Gemfile or available on this machine.
Solución:
sudo apt-get install ruby-mysql2
Una sugerencia que aun no he probado es instalarlo así:
apt-get install redmine redmine-mysql
