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Re: [Xen-users] Xen domUs on Ubuntu

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Subject: Re: [Xen-users] Xen domUs on Ubuntu
From: Mark Williamson <mark.williamson@xxxxxxxxxxxx>
Date: Thu, 18 Oct 2007 18:34:37 +0100
Cc: Luke <secureboot@xxxxxxxxx>
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> I just installed and tried to use the Ubuntu Xen packages, and wondered
> if anyone out there has had similar problems to below.  I'm asking here
> since I'm 90% sure that the problem isn't the package, but my
> setup/configuration instead.
> Firstly, Ubuntu doesn't build ext3 support into their kernel.
> Consequently, I'm passing the same initrd to the domU that is passed to
> dom0 on the command line.  I'm passing this via the config file, obviously.
> Without the initrd, I get a Kernel panic about mounting the root fs.
> This makes sense, as ext3 support doesn't exist.  With the initrd, I get
> to the TLS warning about init, then "Continuing...", then nothing.

Passing an initrd is usually the most straightforward way to get things 
working on modern distros.

> Any ideas what this could be?
> Could I be using an incorrect initrd?  This seems unlikely...
> I've checked that my /etc/fstab is correct...
> In my config file:
> disk = [ 'file:/home/myname/vms/myname.raw,hda1,w']

The domain is probably booting but not sending its console output to the Xen 
virtual serial console.  You could try adding "xencons=tty" to the extra= 
parameter in your domain.  Does that fix things for you?

> I've set up domUs for around 2 years now, which isn't to say I couldn't
> have made a stupid mistake, but I do get the general idea, and I'm not
> getting helpful error messages here.

The console has changed behaviour recently.  It used to grab the /dev/tty1 
device itself so that Xen-unaware distros would Just Work on bootup.  That 
was a slightly rude thing to do in the kernel, so now it uses the 
special /dev/xvc0 node (or, on mainline Linux 2.6.23 /dev/hvc0) as the 
console device.  Pointing Linux at the correct device using console=/dev/xvc0 
to use should solve your problem and allow you to see the output.

*however* you'll notice I've not suggested you do this (at least, initially).  
This is because you'll still need to modify /etc/inittab and /etc/securetty 
in order to be able to start a console on the new /dev/xvc0 and log in.  
Using the "xencons=tty" should make it revert to the older tty-stealing 
behaviour which should Just Work.  You then have the option of moving over 
to /dev/xvc0 once you've switched the config over.  You'll need to move to 
the more polite /dev/xvc0 route if you want to use the framebuffer console.

Hope that helps.  Does this fix things for you?


Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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