OwnCloud is a system of setting up a cloud storage environment. The Sterrewacht provide its own OwnCloud servers, but it is also possible to connect to other “clouds”. SurfDrive is an ownCloud implementation for the joint dutch universities, which you can use using tour ULCN credentials.

The institute implementation of OwnCloud is at https://owncloud.strw.leidenuniv.nl. Use your local username and password. You can access your files through the browser, or set up a client to connect and synchronize files with a local folder.

SurfDrive is a cloud storage service provided by SurfNet, on behalf of the joint dutch universities. It's underlying protocol is that of ownCloud, so you can connect the OwnCloud client to synchronize your files to SurfDrive. The connection url will be: https://surfdrive.surf.nl/files and to log in, select Leiden University and use your ULCN credentials. More details, including apps for Android and iOS, can be found at the SurfDrive website

On our Linux desktops, the OwnCloud client is already installed. It can be started from the Accessories menu, or from the commandline by running the command owncloud. Once started and configured, it will add itself to your desktop session, so it will start automatically when you log in the next time.
It is possible to connect to multiple OwnCloud servers, eg the institute server and SurfDrive. make sure you specify different local directories, unless of course you want to sync the same content to multiple locations.
Also make sure you choose a local directory that is not on your home disk, to avoid quota issues when downloading files. This can be done from the OwnCloud interface by specifying a local data disk directory (like /data2/mysyncdir).
Using OwnCloud as a backup tool for your Linux home is not recommended, at least not directly; in order to be compatible with multiple operating systems and apps, OwnCloud doesn't handle file names starting with dots properly, and file names also don't always appear to be fully case-sensitive, and permissions are not preserved either. Of course you can create a file backup (e.g. tar.gz or zip) of your home, in a location you sync with ownCloud in order to have a remote backup which will preserver special filenames and permissions.

There is now an alternative method for linking your OwnCloud on your Linux desktop: through the Gnome (and Cinnamon) Online Accounts settings panel, you can add an OwnCloud account and after that, you can mount the OwnCloud directory as an external disk in the file manager. This method doesn't do automatic synchronization, but you can copy files to and from the drive to do a selective synchronization.
But be careful if you use both methods at the same time and on the same computer!!

Owncloud clients for Windows, Mac OS X and Linux, as well as apps for Android, iOS and even some other systems, can be found at https://owncloud.com/
SurfDrive offers apps for Android and iOS, as well as specialized clients for Windows and Mac OS X (although there, like on Linux, you can use the OwnCloud client as well).