XEN and PAE dependencies

At the moment I’m trying to get XEN working on my laboratry server at work. This machine is equipped with 2 dual core CPUs and 16 GB RAM and I’m running the 32bit version of Debian/Etch on it. To learn more about XEN I bought a book (in German) before christmas and I read it. Unfortunately this book was not so much detailled to keep me away from some trouble.

Since my machine has more than 4 GB of RAM the use of a PAE enabled hypervisor is adivesed. But when I installed the PAE hypervisor and the XEN kernel image that Etch offers I found out that then the system refuses to boot because of „pae mode mismatch“. The things I learned from this is that there is a strong dependency between PAE and the XEN hypervisor. So I created the following table:

Kernel (dom0 / domU)
PAE enabled PAE disabled
PAE enabled working not working
PAE disabled not working working

If you would run a system with less then 4 GB then the Debian images would fit fine since there is a hypervisor without PAE support. The problem would rise again as soon as you want to use other Linux distributions, all DomU kernels that you find at XenSource are PAE enabled. The same is true for Linux distributions like Fedora or SUSE Linux, all come with DomU kernels but all have PAE support. So you won’t be happy with them on a Debian system without PAE.

So the goal was to get a kernel image that has PAE support. I tried to do it „the Debian way“ and read the chapter about building kernel images on Debian systems in the book of Martin F. Krafft . But with all that I wasn’t able to build the image, all I could do was building a normal kernel image, but not a XEN and PAE enabled kernel image.

I asked for help on the Debian kernel mailing list and I got some good advice how to do it. I followed the instructions and I was sort of successful. A few days later I received a mail that asked if I could post a sort of HowTo, so I started now with this article series.

The next article of this series will go a bit more into the details. But for that I need to be at home and do another „step by step“ installation on my Sarge system.

Autor: Rainer

Diplom-Informatiker, Baujahr 1961, Vater von 2 Kindern, Hundehalter, Sportschütze und Vereinsvorstand, Hobbymusiker (mit zweifelhaftem Erfolg), politisch interessiert, Leseratte, Freizeit-Philosoph und letztlich Blogger.

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