Hi Martin,
sadly you didn’t provide all the required information to give you a better answer. it would be great to know which apps have you enabled and your log fies, anyway I will provide some hints:
you can’t migrate from 5.0.9 to 6.0.9 directly you have to make a step between (5.0.19), the whole migration that you have to do is:
5.0.9 -> 5.0.19 -> 6.0.9 -> 7.0.15 -> 8.0.16 -> 8.1.12 -> 8.2.11 -> 10.0.9 or next week to 10.0.10
You can skip the migrations to 9.0.11 and 9.1.8 when you come from 8.2.11
Please read the reference: https://doc.owncloud.org/server/10.0/admin_manual/maintenance/upgrade.html
and all the release notes too: https://doc.owncloud.org/server/10.0/admin_manual/release_notes.html
The error that you are experimenting is a temporary database to migrate, to avoid it, first make a backup of your database! and then run this command:
./occ upgrade --skip-migration-test -vvv
I’m not sure if the OLD versions have that --skip-migration-test but you can try it.
Additional: (if you don’t want to spend many hours upgrading all the versions)
If you don’t have to many shares and you want to avoid all the migrations steps, I would recommend to install a fresh installation from 10.0.9, copy the files to the same folders of the users and run an occ files:scan --all who will update the oc_filecache.
In this case all the shares will be lost but you could ask to the users to create them again, you can see the existing shares in the oc_share table
I hope that helps.
Carlos