Microsoft supports one flavor of Linux as guest OS in Hyper-V: Novell SUSE Enterprise Linux 10. But to work properly inside the virtual machine Linux needs additional components that Microsoft releases under the name of Linux Integration Components. This package includes the Linux implementation of the Hyper-V VMBus (the same high performance interface that Windows 2003/2008 guest OSes use), the pass-through drivers for network and storage, and some other things.
Microsoft developed this software separately from Hyper-V and while the latter is already available, the Linux Integration Components are not. They were expected last month but the company postponed its release without adding details.
Customers can still install Novell Linux as Hyper-V guest OS but it lacks all the enhancements that makes SUSE the best companion for Windows on the new hypervisor. Without Integration Components the distribution performs just any other, from Red Hat Enterprise Linux to Ubuntu.
For unknown reasons Microsoft also removed the previous version, frozen at Release Candidate 2 milestone since July 11.
This implies that at the moment there’s no way to run a Linux guest OS at its best.