As mentioned in the link about how to upgrade Redmine under the Troubleshooting Upgrades section, you must copy the
installdir/apps/redmine/htdocs/files directory from the old installation to the new one, and if you have installed any plugin, then copy the directories from the
vendor/plugins directory as well. Please, double check that plugins are fully compatible between Windows and Linux versions before copying that folder from one instance to the other.
After copying files from the Windows instance to the Linux one, run the commands below to install plugins and clean the cache and sessions.
ruby bin/rake redmine:plugins RAILS_ENV="production"
ruby bin/rake tmp:cache:clear
ruby bin/rake tmp:sessions:clear
Finally, restart servers for changes to take effect. Remember to use
sudo just in case the stack was installed as root and to replace the
installdir placeholder with the installation path for the stack.
sudo installdir/ctlscript.sh restart
Hope it helps,