I was wondering whether or not XenServer is truly open source. The project has seen quite some back and forth in its history. It was first released in 2006 as a proprietary extension of the Xen hypervisor, called XenEnterprise, by XenSource Inc. Later it became XenServer released by Citrix, still being a proprietary extension of the Xen hypervisor, until Citrix open-sourced it in 2013 and shifting it's business model towards XenServer support. But the information available is confusing.

On the one hand, there is [this announcement][1] by Citrix, saying

> XenServer 6.2 is now fully open source!

and [this slideshow][2] by two Citrix employees which contains some graphics that show everything is open source now.

On the other hand, there is the this XenServer developers page (http://xenserver.org/2013-05-22-15-48-11.html), which says that

> there are a small number of XenServer components which are not able to be open sourced.

These components include the Citrix license server daemon and "various" system drivers and user tools. In addition, I found this article (http://searchitchannel.techtarget.com/tip/Open-source-Xen-vs-Citrix-XenServer) which says, that

> Citrix XenServer is free and comes with some important base functionality, such as the option to perform live migration of VMs. If you're looking for more advanced functions, you need to download Citrix XenCenter. With XenCenter, you'll get advanced provisioning tools and the option to implement high availability -- VMs are automatically restarted if they, or the host they were running on, go down unexpectedly.

This baffles me, because automatic guest domain restarts are already a feature of the Xen hypervisor itself, that XenServer is based on.

For me, open source always meant, that you can download and recompile 100% of the source code on your own and don't have any forced linkage to proprietary software. Is this a misconception of mine? How can this project, that is such strongly interwoven with its commercial mixed-source counterpart, that even seems to resell components being formerly open source, be called "**fully** open source"?

  [1]: https://www.citrix.com/blogs/2013/06/25/xenserver-6-2-is-now-fully-open-source/
  [2]: http://de.slideshare.net/xen_com_mgr/xpus13-pavlicek