You have a Debian 8 installation and get an error like the following when you want to install or update the owncloud client?
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://download.opensuse.org Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4ABE1AC7557BEFF9
W: Failed to fetch http://download.opensuse.org/repositories/isv:/ownCloud:/desktop/Debian_8.0/Release
W: Some index files failed to download. They have been ignored, or old ones used instead.
test -d ~/service || uberspace-setup-svscan
svc -du ~/service/redis
#to prevent or fix the following error "Missing memcache class \OC\Memcache\Redis for local cache"
Last but not least, you have to adapt your */config/config.php* file by adding and adapting the following lines into the configuration array.
Big thanks to the "Google to Owncloud, Contacts and Calendar" entry. This really helps me a lot.
Especially, the link above tells you how to configure your android phone and your mozilla thunderbird (with lightning) to setup the synchronisation with your owncloud.
I gave it a try with "caldav free sync beta" but had a long run of bad luck. After a while, I gave "CalDAV-Sync" a try and it is worth its money since it is working out of the box. Setting up the "carddav" synchronization is also a no brainer, but converting the google contacts to the owncloud contacts is something not that easy for me as a no-gui-user.
For "carddav" (address book) synchronization, you need to install sogo connector.
For "caldav" (calendar) synchronization, you need to install "lightning". The "howto" is described in the first link above.
I found one issue in my owncloud configuration file (config/config.php) and could solve it by adding "1 => 'my.owncloud.domain:443'" to the "trusted domain" array key.
So, I really gave it a try and invested multiple hours. Either my spirit is not strong enough today, or it is currently not possible to synchronize owncloud 8.0.2 calenders with other applications.
To calm me down, here is a list of possible problems that are the reasons I failed currently with my mission.