Hello,
I've tried the upgrade and here's is my log:
First, I've made backups (psql and /usr/share/redmine directory) and
stop my redmine service (through apache2).
Then, I've tried the upgrade and I had this message:
> Could not find gem 'rails (~> 4.1.4) ruby' in the gems available on
this machine.
As I've seen that in Jessie, rails' version is 4.1.8, so I've put it
into the file /usr/share/redmine/Gemfile.
Then, I've run directly 'bundle install' from this directory to check
that gems were well installed and I've found some compatibility issue
with my plugins, but I was able to fix them by editing the plugins'
Gemfile.
After that, 'apt upgrade' were able to finish the work.
Many thanks, good work !
Adrien Dorsaz