Initially (+1 year ago), I installed oC 8.0.4 via opensuse feed on Ubuntu 14.04 server. All worked fine. Now I tried to upgrade to 8.2.1 using the web interface upgrade interface. Step 1-3 went fine, but the database (mysql) upgrade failed. Meanwhile I believe the entire /var/www/owncloud content seems messed up.
Bottomline, I like to install latest 9.1 now. However I don't really know which version was last installed since I did a couple of upgrades already after initial installation (8.0.4). config/config.php says 'version' => '8.1.9.2'.
Now ... how can I install install 9.1 and migrate/upgrade the database from 8.1.9.2 to 9.1?
Normally you do one major upgrade to the other. From 8.0->8.1->8.2->9.0 (make sure all calendars and contacts are properly converted) -> 9.1.
The web-interface upgrade is not the best, more reliably are manual upgrades: - remove all files/folders, except data/ and config/ - download and extract next major version from https://owncloud.org/changelog - run sudo -u www-data php /var/www/owncloud/occ upgrade
Don't forget to make a backup before starting the upgrade procedure. In the current state, get the code of the latest OC 8.1.x and make sure your setup runs before proceeding to the next upgrade.