Migrate owncloud 10 to nextcloud 12

[MichaIng]

See here: Migration from Owncloud 9.1.6 to Nextcloud 10.0.5 fails - #2 by BernhardPosselt

Seems the newest owncloud updates broke upgrade paths again. Try to change back the owncloud version in config.php as mentioned:

@Patrick_Morgenstern

In my case it was the same problem. As a workaround I modified the version of my owncloud virtually to 9.1.5.2. This can be done by modifying the file config/config.php in your owncloud installation directory (modify the string ‘version’ => ‘9.1.6.2’ to ‘version’ => ‘9.1.5.2’). After this you are able to manually install nextcloud (haven’t tried this with the installer method).

About your first attempt oc 10.0.1 => nc 12. The migration page clearly says:

Note that ownCloud 10.0.1 can not yet be migrated to Nextcloud 12, we are still testing this upgrade path to make sure it is 100% reliable!

Hopefully this will be possible soon. Seems that every minor version upgrade of owncloud (on all major versions) breaks the migration until it is tested and fixed. To avoid misunderstandings, the last possible minor version for migration should be added on migration page e.g.:

...
ownCloud 9.1.0 to 9.1.5 is compatible with Nextcloud 10.0.x
ownCloud 10.0.0 is compatible with Nextcloud 12.0.x

or adding some hint which oc version is the last successfully tested one.