problem creating my 1st VM

[Guillaume]

Hi list,
I' trying to create my first vm with Xen, and I experience some problems.
I follow some How to's  and xen docs to build my own config file, but
maybe, there are some errors inside it.
I have the following problem, after i start my guest domain, the
kernel boot & then a kernel panix is displayed :

VFS: Cannot open root device "hda1" 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)

I try to start this Virtual machine from vmware workstation where i
install Xen (Dom0 work perfectly).

My config is make up of these lines :
kernel = "/boot/vmlinuz-2.6.20-2936.fc7xen"
root = "/dev/hda1 ro"
name = "test_Linux"
cdrom = "/dev/cdrom"
memory = "128"
builder = "linux"
name = "linux"
disk = [ "file:/xenroot/linux/linux.xdi,hda1,w" ]

Additionnals questions :
a) Does i must use a modified Xen linux kernel, or, can I use a
"normal/standard" kernel to boot up my VM?
b) Is it possible to start a fresh install of Fedora directly from dvd
in a guest domain (I mean without creating & mounting disk image/VM
partition and copying root file system in it? If yes, how ?

Thanks for your replyes.

[Olivier Renault]

Guillaume wrote:
> Hi list,
> I' trying to create my first vm with Xen, and I experience some problems.
> I follow some How to's  and xen docs to build my own config file, but
> maybe, there are some errors inside it.
> I have the following problem, after i start my guest domain, the
> kernel boot & then a kernel panix is displayed :
>
> VFS: Cannot open root device "hda1" 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)
>
> I try to start this Virtual machine from vmware workstation where i
> install Xen (Dom0 work perfectly).
>
> My config is make up of these lines :
> kernel = "/boot/vmlinuz-2.6.20-2936.fc7xen"
> root = "/dev/hda1 ro"
> name = "test_Linux"
> cdrom = "/dev/cdrom"
> memory = "128"
> builder = "linux"
> name = "linux"
> disk = [ "file:/xenroot/linux/linux.xdi,hda1,w" ]
>
> Additionnals questions :
> a) Does i must use a modified Xen linux kernel, or, can I use a
> "normal/standard" kernel to boot up my VM?
> b) Is it possible to start a fresh install of Fedora directly from dvd
> in a guest domain (I mean without creating & mounting disk image/VM
> partition and copying root file system in it? If yes, how ?
>
> Thanks for your replyes.

Hi,

I am not sure how you have installed your VM ? You should try to 
reinstall the VM using virt-install (command line) / virt-manager (GUI).

It is not great to try a virtualisation solution inside another one ( 
you may have strange behaviour / poor performance ).

a) You need to run the xen kernel in order to use xen.

b) To install a paravirtualise VM you will need to have an install tree 
exported as http. You can simply mount the DVD on /var/www/html and 
start the http server.

You may want to read
http://fedoraproject.org/wiki/Docs/Fedora7VirtQuickStart

Good luck,
Olivier

[Mark Nielsen]

In addition, you're presenting the disk as hda1. You probably mean to 
present the disk as hda so the partition hda1 on hda isn't confused. As 
Olivier has pointed out though, you appear to have many other issues to 
work through as well.

Mark

Olivier Renault wrote:
> Guillaume wrote:
> > Hi list,
> > I' trying to create my first vm with Xen, and I experience some 
> > problems.
> > I follow some How to's  and xen docs to build my own config file, but
> > maybe, there are some errors inside it.
> > I have the following problem, after i start my guest domain, the
> > kernel boot & then a kernel panix is displayed :
> >
> > VFS: Cannot open root device "hda1" 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)
> >
> > I try to start this Virtual machine from vmware workstation where i
> > install Xen (Dom0 work perfectly).
> >
> > My config is make up of these lines :
> > kernel = "/boot/vmlinuz-2.6.20-2936.fc7xen"
> > root = "/dev/hda1 ro"
> > name = "test_Linux"
> > cdrom = "/dev/cdrom"
> > memory = "128"
> > builder = "linux"
> > name = "linux"
> > disk = [ "file:/xenroot/linux/linux.xdi,hda1,w" ]
> >
> > Additionnals questions :
> > a) Does i must use a modified Xen linux kernel, or, can I use a
> > "normal/standard" kernel to boot up my VM?
> > b) Is it possible to start a fresh install of Fedora directly from dvd
> > in a guest domain (I mean without creating & mounting disk image/VM
> > partition and copying root file system in it? If yes, how ?
> >
> > Thanks for your replyes.
>
> Hi,
>
> I am not sure how you have installed your VM ? You should try to 
> reinstall the VM using virt-install (command line) / virt-manager (GUI).
>
> It is not great to try a virtualisation solution inside another one ( 
> you may have strange behaviour / poor performance ).
>
> a) You need to run the xen kernel in order to use xen.
>
> b) To install a paravirtualise VM you will need to have an install 
> tree exported as http. You can simply mount the DVD on /var/www/html 
> and start the http server.
>
> You may want to read
> http://fedoraproject.org/wiki/Docs/Fedora7VirtQuickStart
>
> Good luck,
> Olivier
>
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> Fedora-xen mailing list
> [e-mail]
> https://www.redhat.com/mailman/listinfo/fedora-xen

[Dustin Henning]

It has been a while since I have used a paravirtualized vm, so my responses
will be vague, but perhaps helpful.
Regarding your original install, both previous responses made good points.
However, I thought some additional explanation might be helpful:
a)
-The kernel line you put in your config makes your vm boot that kernel (the
one on your local disk), so you are already using a xen kernel to boot that
vm.
-There are ready made xen compatible installs of OSes on disk images
available for download at various places, you should be able to find
instructions on how to get thee images into your vm's virtual drive as well.
You may already know this base on your question, but I wasn't sure (I
learned xen before it came on distros and I haven't read the fedora
documentation to see if it  mentions that or where you are copying the files
from for the vms you create).
-Personally, I prefer to use partitions (or even disks) as virtual disks.
This can be done by using (for example) phy:/dev/hdb or phy:/dev/hda4 or
dev:/mapper/lvmvolgroup/lvmvol (or something, LVM certainly makes the
management of multiple virtual but physical disks more manageable) instead
of file:/xenroot/linux/linux.xdi in the first portion of the disk=
arguments.
b)
-You can use a normal/standard kernel in an HVM vm.  This requires that you
have a machine with hardware virtualization, but it allows you to install
windows, boot with a non-xen livecd, etc.  I think there is an example like
/etc/xen/xmexample.hvm for these situations.  In such a case, you wouldn't
have to fdisk the intended virtual partition because the installer you use
when you initially create the machine (windows, linux, whatever) would take
care of that.
etc)
As mentioned by another user, the virtual machine installation executables
(virsh-install/virt-install?) will create a virtual machine that is more
manageable with fedora tools and uses xen capabilities.  I don't know where
config files for these domains are installed, and I prefer the manual
creation via config files and whatnot so I have more control when the time
comes for major changes.  I believe the installer provided on Fedora can
make paravirtualized and hvm machines, and from the sound of a previous
response, it may take care of copying the filesystem on paravirtualized
machines as well.
I hope this helps or at least doesn't hurt.
Dustin

-----Original Message-----
From: [e-mail] [mailto:[e-mail]]
On Behalf Of Guillaume
Sent: Friday, October 26, 2007 06:01
To: [e-mail]
Subject: [Fedora-xen] problem creating my 1st VM

Hi list,
I' trying to create my first vm with Xen, and I experience some problems.
I follow some How to's  and xen docs to build my own config file, but
maybe, there are some errors inside it.
I have the following problem, after i start my guest domain, the
kernel boot & then a kernel panix is displayed :

VFS: Cannot open root device "hda1" 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)

I try to start this Virtual machine from vmware workstation where i
install Xen (Dom0 work perfectly).

My config is make up of these lines :
kernel = "/boot/vmlinuz-2.6.20-2936.fc7xen"
root = "/dev/hda1 ro"
name = "test_Linux"
cdrom = "/dev/cdrom"
memory = "128"
builder = "linux"
name = "linux"
disk = [ "file:/xenroot/linux/linux.xdi,hda1,w" ]

Additionnals questions :
a) Does i must use a modified Xen linux kernel, or, can I use a
"normal/standard" kernel to boot up my VM?
b) Is it possible to start a fresh install of Fedora directly from dvd
in a guest domain (I mean without creating & mounting disk image/VM
partition and copying root file system in it? If yes, how ?

Thanks for your replyes.

[Guillaume]

2007/10/26, Guillaume :
> Hi list,
> I' trying to create my first vm with Xen, and I experience some problems.
> I follow some How to's  and xen docs to build my own config file, but
> maybe, there are some errors inside it.
> I have the following problem, after i start my guest domain, the
> kernel boot & then a kernel panic is displayed :
>
> VFS: Cannot open root device "hda1" 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)

For this problem, it seems that no reference to scsi is made during
DomU boot. Maybe SCSI support is loaded with the initrd image. Is
there a way to give arguments in VM config file to use any initrd
image ? Or I have to "recompile" the kernel and set generic scsi
support not in module !

---
Guillaume

[Dustin Henning]

In the e-mail I just sent, I showed an example for using initrd.
Try that.  However, the virtual hda should not be detected as a generic scsi
device, it should be detected as a generic ide device.  A virtual sda might
be detected as a scsi device, but I don't know if you can even do that in a
paravirtualized environment (I think you can in an HVM, but the virtual BIOS
won't boot to a scsi device in that situation).  The unknown block device
error could be happening because the xdi file is "partitioned" and should be
connected as hda (as previously suggested by another member and again by
myself in my previous [just sent] e-mail) instead of hda1.  If that is the
case, you wouldn't be able to also add an hda2 and might have to use hdb1 if
you need additional partitions / drives on your vm, but if it is
"partitioned" it likely has a swap partition anyway.
    Dustin

-----Original Message-----
From: [e-mail] [mailto:[e-mail]]
On Behalf Of Guillaume
Sent: Friday, October 26, 2007 11:50
To: [e-mail]
Subject: [Fedora-xen] Re: problem creating my 1st VM

2007/10/26, Guillaume :
> Hi list,
> I' trying to create my first vm with Xen, and I experience some problems.
> I follow some How to's  and xen docs to build my own config file, but
> maybe, there are some errors inside it.
> I have the following problem, after i start my guest domain, the
> kernel boot & then a kernel panic is displayed :
>
> VFS: Cannot open root device "hda1" 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)

For this problem, it seems that no reference to scsi is made during
DomU boot. Maybe SCSI support is loaded with the initrd image. Is
there a way to give arguments in VM config file to use any initrd
image ? Or I have to "recompile" the kernel and set generic scsi
support not in module !

---
Guillaume

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