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Re: [Xen-users] Getting linux to boot under XEN

On Saturday 31 March 2007 02:14:22 Petersson, Mats wrote:
> > -----Original Message-----
> > From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx
> > [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of Ian
> > Sent: 30 March 2007 08:40
> > To: xen-users@xxxxxxxxxxxxxxxxxxx
> > Subject: [Xen-users] Getting linux to boot under XEN
> >
> > Hi,
> > I've just started playing around with XEN on my
> > SUSE-10.2/Intel Core-duo
> > system . I'm getting rather confused about what to do, mainly
> > because so much
> > of the documentation I've read doesn't say wither it's
> > talking about full- or
> > para- virtualisation and XEN 2 or XEN 3.
> > I have successfully installed and run Windows XP using this how-to:
> > http://en.opensuse.org/Xen_Full_Virtualization_Example
> > I don't know wether it's really full virtualisation or para
> > (I believe I am
> > right in thinking para-virtualisation is the newer, less
> > resource hungry
> > method available in XEN 3 (which is what SUSE-10.2 runs).
> Para-virtualization is where you take the OS source code and modify
> parts of it to make it "co-operate" with the hypervisor (Virtual Machine
> Monitor/manager or whatever you call the "multi-task between different
> OS's" part of the system). This has always been availabe for Xenified
> versions of Linux.
> Full virtualization doesn't require any changes to the OS's software,
> but for it to not be a royal pain in the butt, you need extra features
> in the processor to "intercept" things that normally can't be "caught"
> by the hypervisor. Since all virtualization involves "lying" to the OS
> in some respects (all OS's want to believe that they are the ONLY OS in
> the machine, for example, and that ALL the memory belongs to this OS).
> This has only been available in Xen 3 (and only with processors that
> have AMD-V or Intel VT).

OK, thanks for explaining that - so since I have an Intel-VT enabled 
processor, I can run full virtualisation on it at reasonable speeds.

> > I've also tried to run SUSE 10.2, Ubuntu Dapper (GUI install)
> > and Ubuntu 7.04
> > (Feisty Fawn) Beta (alternate install) and FreeBSD 6.2 using
> > the same method.
> > FreeBSD booted from the install CD but the bootloader just
> > kept throwing
> > bootloader errors in loop.
> > All 3 Linux installers just showed a blank screen and hung.
> One possible cause is that the boot-loader for all those Linux
> distributions are using "big real-mode", which is essentially a way to
> be able to load data (or code) above 1MB, whilst still using the BIOS to
> read the hard-disk. Because Intel's CPU's don't support this mode very
> well in virtualization, installing can be a problem.
> You may find that you can use QEMU to install, or you may be able to get
> past it by simply using "nographics" installation (sometimes, the only
> bit of code ever to use big-realmode is the bit that loads the fancy
> graphics!).

I thought the Ubuntu Alternative install was a text mode installation? It did 
exactly the same thing as the full install, so I might have to look into the 
QEMU install instead for Ubuntu. Same for FreeBSD - it doesn't have a GUI 
installer at all.

Thanks for your suggestions!


> > I was expecting XP to be the hardest to run under XEN, but
> > it's ended up being
> > the easiest! (at least the way I've done things).
> >
> > So, my question is, are the instructions mentioned above only
> > going to work
> > for Windows, or should they work for other OSes
> > (Linux/FreeBSD) as well?
> > I've read a lot of stuff about downloading special kernels
> > and initrd files to
> > run Linux - was that just for XEN2 or do you need to the same
> > in XEN 3?
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