Xen users - Oct 2007 - Creating initial file system for a new Xen domain

I''ve moderately familiar with using XenSource distributions and also
administering Xen with tools like virt-manager on Fedora.  However now
I''m building xen (3.0.3) from source and trying to use what I built
myself.

My first question is why is it that tools like virt-manager don''t work
when I boot to the Xen hypervisor and Dom0 I built?  The virt-manager
I''m trying to use is from FC6.  Is this known to be generally
impossible for some reason (missing APIs), or is it supposed to work
at least sometimes?  What are my other options for tools that will
create a Xen domain configuration file...I know this can be done by
hand but there must be more friendly tools out there somewhere...

My second question is very basic, forgive me: using just the tools
that are built with the xen source distribution, how does one install
Linux on a DomU?  I know you just point to a kernel/ramdisk in the
domain configuration file, but what about the root filesystem?  Using
XenExpress and virt-manager, I always run through a Linux install, so
that populates the root filesystem with all the stuff essential for
the system.  I know that you can point a domain to a partition in the
domain''s configuration file, but how do you populate that partition?

My third and final question is: when using virt-install a file-backed
VBD is created for the DomU.  The domain''s configuration file has:
disk = [ ''tap:aio:/vmdisks/Fedora6Guest3,xvda,w'', ]
I''d like to mount this in Dom0.  I execute
xm block-attach 0 tap:aio:/vmdisks/Fedora6Guest3 /dev/xvda1 w 0
which seems to work.  But how do mount the device /dev/xvda1 in Dom0?
I think the problem is that it isn''t really an ext3 filesystem,
because it contiains multiple partitions (one for /boot and one for
/), so I can''t just say
mount -t ext3 /dev/xvda1 /tmp/mountpoint

Thanks!
Dave

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> I''ve moderately familiar with using XenSource distributions and
also
> administering Xen with tools like virt-manager on Fedora.  However now
> I''m building xen (3.0.3) from source and trying to use what I
built
> myself.
>
> My first question is why is it that tools like virt-manager don''t
work
> when I boot to the Xen hypervisor and Dom0 I built?  The virt-manager
> I''m trying to use is from FC6.  Is this known to be generally
> impossible for some reason (missing APIs), or is it supposed to work
> at least sometimes?  What are my other options for tools that will
> create a Xen domain configuration file...I know this can be done by
> hand but there must be more friendly tools out there somewhere...
I''m not entirely sure, to be honest.  I would guess that maybe
virt-manager
isn''t up to date enough to use your hypervisor version, but
I''m not really
familiar enough with it to say for sure.  Does xm, etc work correctly for 
you?

What distro are you on?  You could perhaps try updating to a newer 
virt-manager (e.g. the one from FC6?  Or from source, or from SVN?).
> My second question is very basic, forgive me: using just the tools
> that are built with the xen source distribution, how does one install
> Linux on a DomU?  I know you just point to a kernel/ramdisk in the
> domain configuration file, but what about the root filesystem?  Using
> XenExpress and virt-manager, I always run through a Linux install, so
> that populates the root filesystem with all the stuff essential for
> the system.  I know that you can point a domain to a partition in the
> domain''s configuration file, but how do you populate that
partition?
If you want an HVM domU, you create a configuration file that points to the 
virtual disk of the domain, and gives it a virtual cdrom drive pointing to 
the .iso of the install CD.  Then proceed basically as for a normal machine.

If you want a PV domU, the process varies.  To install a Redhat-type guest, 
you ferret around on the install CD until you find the installation kernel 
and initrd for Xen, then create a config file that boots these, passing it 
the virtual disks for it''s install destination and the .iso file
(don''t pass
this as a cdrom, it won''t work).  For other guests, there are other
ways -
you can also install RH-like (and maybe other) RPM distros using
"rpmstrap".
And you can install Debian-likes using "debootstrap".  Both of these
tools
can be used to drop a distro install into a filesystem tree (e.g. a mounted 
virtual disk partition).

Various distros (Redhat, SuSE, etc) also provide their own tools for 
installing a guest.  The libvirt folks were looking at supporting SuSE guests 
from virt-manager, which would be cool.
> My third and final question is: when using virt-install a file-backed
> VBD is created for the DomU.  The domain''s configuration file has:
> disk = [ ''tap:aio:/vmdisks/Fedora6Guest3,xvda,w'', ]
> I''d like to mount this in Dom0.  I execute
> xm block-attach 0 tap:aio:/vmdisks/Fedora6Guest3 /dev/xvda1 w 0
> which seems to work.  But how do mount the device /dev/xvda1 in Dom0?
> I think the problem is that it isn''t really an ext3 filesystem,
> because it contiains multiple partitions (one for /boot and one for
> /), so I can''t just say
> mount -t ext3 /dev/xvda1 /tmp/mountpoint
Easiest way is to use the lomount command; it''s included in the Xen 
distribution and originally came from the Qemu distribution.  It allows you 
to select a partition from a virtual disk image and specify a directory to 
mount its filesystem on.  This uses the Linux loopback device.  Make sure you 
unmount before booting the guest, or bad things may happen ;-)

Hope that helps!

Cheers,
Mark
-- 
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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http://lists.xensource.com/xen-users

Thanks for your help, I understand and got this working now.

Dave

On 10/19/07, Mark Williamson <mark.williamson@cl.cam.ac.uk>
wrote:
> > I''ve moderately familiar with using XenSource distributions
and also
> > administering Xen with tools like virt-manager on Fedora.  However now
> > I''m building xen (3.0.3) from source and trying to use what I
built
> > myself.
> >
> > My first question is why is it that tools like virt-manager
don''t work
> > when I boot to the Xen hypervisor and Dom0 I built?  The virt-manager
> > I''m trying to use is from FC6.  Is this known to be generally
> > impossible for some reason (missing APIs), or is it supposed to work
> > at least sometimes?  What are my other options for tools that will
> > create a Xen domain configuration file...I know this can be done by
> > hand but there must be more friendly tools out there somewhere...
>
> I''m not entirely sure, to be honest.  I would guess that maybe
virt-manager
> isn''t up to date enough to use your hypervisor version, but
I''m not really
> familiar enough with it to say for sure.  Does xm, etc work correctly for
> you?
>
> What distro are you on?  You could perhaps try updating to a newer
> virt-manager (e.g. the one from FC6?  Or from source, or from SVN?).
>
> > My second question is very basic, forgive me: using just the tools
> > that are built with the xen source distribution, how does one install
> > Linux on a DomU?  I know you just point to a kernel/ramdisk in the
> > domain configuration file, but what about the root filesystem?  Using
> > XenExpress and virt-manager, I always run through a Linux install, so
> > that populates the root filesystem with all the stuff essential for
> > the system.  I know that you can point a domain to a partition in the
> > domain''s configuration file, but how do you populate that
partition?
>
> If you want an HVM domU, you create a configuration file that points to the
> virtual disk of the domain, and gives it a virtual cdrom drive pointing to
> the .iso of the install CD.  Then proceed basically as for a normal
machine.
>
> If you want a PV domU, the process varies.  To install a Redhat-type guest,
> you ferret around on the install CD until you find the installation kernel
> and initrd for Xen, then create a config file that boots these, passing it
> the virtual disks for it''s install destination and the .iso file
(don''t pass
> this as a cdrom, it won''t work).  For other guests, there are
other ways -
> you can also install RH-like (and maybe other) RPM distros using
"rpmstrap".
> And you can install Debian-likes using "debootstrap".  Both of
these tools
> can be used to drop a distro install into a filesystem tree (e.g. a mounted
> virtual disk partition).
>
> Various distros (Redhat, SuSE, etc) also provide their own tools for
> installing a guest.  The libvirt folks were looking at supporting SuSE
guests
> from virt-manager, which would be cool.
>
> > My third and final question is: when using virt-install a file-backed
> > VBD is created for the DomU.  The domain''s configuration file
has:
> > disk = [ ''tap:aio:/vmdisks/Fedora6Guest3,xvda,w'', ]
> > I''d like to mount this in Dom0.  I execute
> > xm block-attach 0 tap:aio:/vmdisks/Fedora6Guest3 /dev/xvda1 w 0
> > which seems to work.  But how do mount the device /dev/xvda1 in Dom0?
> > I think the problem is that it isn''t really an ext3
filesystem,
> > because it contiains multiple partitions (one for /boot and one for
> > /), so I can''t just say
> > mount -t ext3 /dev/xvda1 /tmp/mountpoint
>
> Easiest way is to use the lomount command; it''s included in the
Xen
> distribution and originally came from the Qemu distribution.  It allows you
> to select a partition from a virtual disk image and specify a directory to
> mount its filesystem on.  This uses the Linux loopback device.  Make sure
you
> unmount before booting the guest, or bad things may happen ;-)
>
> Hope that helps!
>
> Cheers,
> Mark
> --
> 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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Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

Would you mind sharing what all you did to resolve the problem ? Where you
able to use virt-manager with compiled xen ?

On 10/24/07, David Stone <unclestoner@gmail.com>
wrote:
>
> Thanks for your help, I understand and got this working now.
>
-- 
regards,

Anand Gupta


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Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

> Would you mind sharing what all you did to resolve the problem ? Where you
> able to use virt-manager with compiled xen ?
Sure.  For the issue of using virt-manager with compiled xen, I didn''t
spend more time on it and didn''t get it to work because I got used to
using the vanilla xen tools  virt-manager hangs when I launch it, and
the other virt tools one gets with FC6 also don''t work.

For mounting the domU''s disk file, lomount wasn''t working for
me
because I had the domU configured to use an LVM.  For domUs I have
created since then, I don''t configure domUs to use LVMs, and lomount
works in that case.  Also, I sometimes use a Dom0 partition to back
the DomU''s virtual disk, in which case lomount can also be used to
mount the virtual disk in Dom0.

I was able to get the DomU I _created_ with virt-manager to run with
compiled Xen...the only thing that doesn''t work is graphical output
from the DomU.  I needed to change the DomU''s inittab to start at
runlevel 3.  Unfortunately I couldn''t mount it''s file systems
(see
above), so to do this I had to start the DomU while running a network
sniffer in Dom0 so I could see the IP address the DomU got from DHCP
(since I didn''t have any static IPs handy).  Then I ssh''d into
the
DomU and changed inittab :)

Dave

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