Re: [Xen-users] how to boot a para-virtulized vm from cdrom after installation

["Nick Couchman" <Nick.Couchman@xxxxxxxxx>]

>>> On 2012/10/08 at 10:08, Alexandre Kouznetsov <alk@xxxxxxxxxx> wrote:

> Hello.
> 
> El 06/10/12 08:38, jun hu escribió:
>> how to boot a para-virtulized vm from cdrom after installation?
> 
> In short, it does not work that way.
> 
> When you decide "where to boot from", it implies there is some piece
of 
> code (BIOS, for example) that will look for a bootloader on some
device. 
> This is perfectly valid in HVM mode of operation, but not in PV.
> 
> In case of Para-Virtualized DomU, the hypervisor itself loads the 
> kernel, specified in the config file. There is no BIOS or bootloader

> residing in the MBR of a block device. There is no no such thing as 
> "boot device" or "boot order".
> 
> You can try this:
> 1. Hard way. Set up a new, completely new, HVM DomU. Attach your
former 
> PV DomU to it and boot form CD.
> 
> 2. Depends on what you need to achieve over your DomU, it almost 
> certainly possible to be done from Dom0.
> 

It's worth noting that some of the Xen management tools, like
virt-manager (open source Xen) and XenCenter (XenServer/XCP) try to help
you with this process.  If you choose to boot one of these from a CD,
the management tool goes out and looks in common locations for a
Xen-based kernel, copies the kernel and initrd over to a temp location,
and boots the VM in PV mode with the CD/DVD attached.  This makes the
process transparent to the end user, but it still is not truly booting
off of a CD.  Most modern Linux distributions have a Xen kernel and
initrd located somewhere on the install media for just this purpose.

-Nick



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