move postgresql 9.4 cluster to new server
I solved it like this:


I had to restore the old config too in 

/etc/postgresql/9.4/main

Then I could start the old main cluster with

pg_ctlcluster 9.4 main start

Then I had to update redmine:

cd /usr/share/redmine


and start

bundle exec rake db:migrate RAILS_ENV=production

check if redmine is working correctly in your browser, Now you can upgrade postgresql to 11. first dump the database with

sudo -u postgres pg_dumpall &gt; /root/full_dump.sql  

remove postgres 9.4 and install postgres 11, then 

sudo -u postgres psql -d postgres &lt; /root/full_dump.sql
/etc/init.d/postgresql restart

check /var/log/redmine/default/production.log for any errors, for example check in /etc/redmine/default/database.yml if redmine is still trying to connect on port 5433