Re: [Xen-users] Xen installation on Ubuntu

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2015-09-18 at 17:59 -0400, Carl Patenaude Poulin wrote:
> Hi all,
> 
> I'm trying to install Xen for my senior undergrad project but I'm
> hopelessly stuck. I'd appreciate some help troubleshooting my setup.
> 
> From Ubuntu 15.04, I've installed the xen-hypervisor-amd64 package.
> I then rebooted, and in Grub2 I picked the entry "Ubuntu GNU/Linux,
> with Xen hypervisor". Here is the result:
> 
> > [    3.551868] i8042: No controller found
> > [    3.552657] mce: Unable to init device /dev/mclog (rc: -16)
> > starting version 219
> > error: /dev/sda: No medium found
> > error: /dev/sda: No medium found
> > Gave up waiting for root device. Common problems:
> > - Boot args (cat /proc/cmdline)
> >   - Check rootdelay= (did the system wait long enough?)
> >   - check root= (did the system wait for the right device?)
> > - Missing modules (cat /proc/modules: ls /dev)
> > ALERT!  /dev/disk/by-uuid/899b8dce-8b47-40a4-ba20-ef4d27b9d128 does not
> > exist.  Dropping to a shell!
> > 
> > 
> > BusyBox v1.22.1 (Ubuntu 1:1.22.0-9ubuntu1) built-in shell (ash)
> > Enter 'help' for a list of built-in commands.
> > 
> > (initramfs) cat /proc/cmdline
> > placeholder root=899b8dce-8b47-40a4-ba20-ef4d27b9d128 ro quiet splash
> 
> Looking at /proc/cmdline, there's some interesting stuff:
> 1. "placeholder" instead of a kernel name;

This is an expected workaround for a difference between grub1 and grub2
(one includes "argv[0]" in the command line and the other doesn't, so this
sacrificial placeholder is used for the one which isn't, or something like
that)

> 2. "rootdelay=" is not specified.

And it was with a native boot?

> I'm not sure where that command line is specified, but the values
> above are the default after installing the xen-hypervisor-amd64
> package.

It is constructed by update-grub using variables from /etc/default/grub.
/etc/grub.d/??_linux_xen (where ?? is usually 20) is the actual generator.

Unless you are setting GRUB_CMDLINE_LINUX_XEN_REPLACE or
 GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT in /e/d/grub then it should be
using the same command line for Linux as dom0 as it does for native, I
think.

> When booting with regular Ubuntu without Xen, /dev/sda mounts just
> fine, with the UUID specified in the error message
> (899b8dce-8b47-40a4-ba20-ef4d27b9d128).
> 
> I also tried booting Xen over EFI, without GRUB intervening. I moved
> the xen-*.efi file from /boot to /boot/efi/EFI/xen. Unfortunately,
> there wasn't a xen-*.cfg config file around, and writing one from
> scratch seems WAAAY above my skill level.

Are you booting on an EFI system then? If so then I'm afraid this is the
correct route.

Writing a xen-*.cfg is pretty trivial. Have you seen 
http://xenbits.xen.org/docs/unstable/misc/efi.html ?

Ian.


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