Hi all,
In the meantime I managed to get it working. I already figured out that the migration from CentOS7 to Ubuntu will not work when using the provided backup script. It will throw errors all over.
In the end I’ve got it working by following the steps Johannes provided. The problems with restoring the database got covered by making a complete dump of the database on the CentOS7 environment with the function pg-dump. Restoring the database succeeded when giing a couple of extra parameters to truncate the database first.
Making the dump
pg_dump -Fc mydb > db.dump
Restoring the database
pg_restore --verbose --clean --no-acl --no-owner -h localhost -U myuser -d my_db db/latest.dump
I needed to restore the dump as the postgresql zammad user.
After that everything works like a charm.
Thanks for the provided support.