PRECISE 12.04

2) VirtualBox expects headers to be available in /lib/modules/$(uname -r)/build/include/linux. This was not the case (no 'build' directory at all), so I symlinked /usr/src/linux-headers-3.4.55-rtai-2/ to /lib/modules/3.4.55-rtai-2/build

I think it was number 2 that fixed it.

Yeah that will be it.

When you build a kernel from sources and run make modules_install , you have 2 symlinks, build and source in /lib/modules/kernelflavour/ which point back to the kernel sources, normally /usr/src/linux.

Creating a deb package from the kernel, often ends up with orphaned symlinks which get deleted when installed on a system without the kernel sources

regards

Well, I can confirm that it works. Problem solved, ready for the next one