VFS: Cannot open root device "sda1" or unknown-block(0, 0)

[Haifeng He]

Hi, All

I followed the steps in Fedora7VirtQuickStart to install Xen on Fedora 7.
I downloaded couples of file system image from http://jailtime.org/. However,
every time I tried to create guest OS using those file system image, I got error
messages:

VFS: Cannot open root device "sda1" or unknown-block(0,0)
Please append a correct "root=" boot option
Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

An example of Xen configure is:

kernel = "/boot/vmlinuz-2.6.20-2936.fc7xen"
memory = 256
name = "fedora.fc6"
vif = [ '' ]
dhcp = "dhcp"
disk = ['file:/xen/fedora/fedora.fc6.img,sda1,w',
'file:/xen/fedora/fedora.swap,
sda2,w']
root = "/dev/sda1 ro"

Having been googling on this topic for a while, but still not getting the right
answer for it. Any help will be appreciated.

Thanks

Haifeng

[Eduardo Habkost]

On Thu, Oct 11, 2007 at 10:43:22AM -0700, Haifeng He wrote:
>  Hi, All
>  
>  I followed the steps in Fedora7VirtQuickStart to install Xen on Fedora 7.
>  I downloaded couples of file system image from http://jailtime.org/. However,
>  every time I tried to create guest OS using those file system image, I got error
>  messages:
>  
>  VFS: Cannot open root device "sda1" or unknown-block(0,0)
>  Please append a correct "root=" boot option
>  Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
>  
>  An example of Xen configure is:
>  
>  kernel = "/boot/vmlinuz-2.6.20-2936.fc7xen" 
You don't have a initrd image that contains the block device and
filesystem modules.

I expect the images you have downloaded have a valid grub configuration
inside it. If they have it, you can use:

bootloader = "/usr/bin/pygrub"

Instead of specifying a kernel that is outside the disk image. Pygrub
will be able to read grub configuration and kernel/initrd images from
inside the disk image.

-- 
Eduardo

[Haifeng He]

On 10/11/07, Eduardo Habkost <ehabkost(a)redhat.com&gt; wrote:
>  On Thu, Oct 11, 2007 at 10:43:22AM -0700, Haifeng He wrote:
>  > Hi, All
>  >
>  > I followed the steps in Fedora7VirtQuickStart to install Xen on Fedora 7.
>  > I downloaded couples of file system image from http://jailtime.org/. However,
>  > every time I tried to create guest OS using those file system image, I got error
>  > messages:
>  >
>  > VFS: Cannot open root device "sda1" or unknown-block(0,0)
>  > Please append a correct "root=" boot option
>  > Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
>  >
>  > An example of Xen configure is:
>  >
>  > kernel = "/boot/vmlinuz-2.6.20-2936.fc7xen"
>
>  You don't have a initrd image that contains the block device and
>  filesystem modules.
>
>  I expect the images you have downloaded have a valid grub configuration
>  inside it. If they have it, you can use:
>
>  bootloader = "/usr/bin/pygrub"
>
>  Instead of specifying a kernel that is outside the disk image. Pygrub
>  will be able to read grub configuration and kernel/initrd images from
>  inside the disk image.
>  
Thank you for your reply. I tried to include bootloader = "/usr/bin/pygrub"
in my configuration but I got an error message "Error: Boot loader
didn't return any data!".
I was able to boot the same image on a Ubuntu system with Xen
installed from source.
Do I need to do something special on Fedora-Xen? Or there is a way that I
can add block device and filesystem modules into the initrd image?

Thanks
Haifeng

>  --
>  Eduardo
>

[Eduardo Habkost]

On Fri, Oct 12, 2007 at 10:06:43AM -0700, Haifeng He wrote:
<snip>
>  >
>  > I expect the images you have downloaded have a valid grub configuration
>  > inside it. If they have it, you can use:
>  >
>  > bootloader = "/usr/bin/pygrub"
>  >
>  > Instead of specifying a kernel that is outside the disk image. Pygrub
>  > will be able to read grub configuration and kernel/initrd images from
>  > inside the disk image.
>  >
>  
>  Thank you for your reply. I tried to include bootloader = "/usr/bin/pygrub"
>  in my configuration but I got an error message "Error: Boot loader
>  didn't return any data!".
>  I was able to boot the same image on a Ubuntu system with Xen
>  installed from source.
>  Do I need to do something special on Fedora-Xen? Or there is a way that I
>  can add block device and filesystem modules into the initrd image? 
I took a look at the config file shipped with Fedora images on the site
you mentioned. It looks like it expects you to have a pre-compiled domU
kernel that contains all needed modules, on you host /boot directory. I
don't know which kernel image the author of those images expects you
to use.

Some things you can try:

- Checking the instructions on the README.txt inside the image, as noted
  on <http://jailtime.org/download:fedora:fc6>;. Maybe there are some
  clues there; or
- Try to generate a initrd that will contain all needed modules. You can
  play with the --omit-* and --with options of mkinitrd to get a initrd
  with the right modules; or
- Try using the Xen kernel and initrd from the FC-6 repository:
  http://download.fedora.redhat.com/pub/fedora/linux/core/6/i386/os/images/...
  or
- Get a domU kernel with all needed modules compiled as builtin (so
  you don't need a initrd) from somewhere, or compile a domU kernel this
  way; or
- Put a valid grub configuration (and a kernel-xen package) inside the
  image, to get pygrub to work; or
- Use virt-manager and install your own FC-6 system instead of using
  the downloaded image.

-- 
Eduardo