[Fedora-xen] Where's my VM gone?

[Daniel P. Berrange]

On Sat, Dec 29, 2007 at 03:08:00PM +0000, Evan Lavelle wrote:
> I'm on F8, and decided to have a go a creating a PV guest on LVM (x86_64 
> F8 DomU on x86_64 F8 Dom0) using virt-install. virt-manager doesn't 
> appear to do anything on my (out-of-the-box) F8 Dom0; you just enter a 
> root password, and the GUI disappears. I've already done a couple of 
> other guests 'manually' on this DomU, without problems.
> 
> It took me a few hours to get through installation, because of various 
> problems with NFS firewalls, DNS problems, and so on. I had to abort the 
> install several times. when this happened, my previous VM name was 'used 
> up'. xm list showed a zombie domain with that name, even if the 
> installation had barely started. I couldn't start a new installation 
> with the same name, because virt-install complained that the VM already 
> existed.
> 
> So, I Googled around, found others with the same problem, and found out 
> that I could remove the zombie entry with 'virsh undefine'. I eventually 
> created a VM with the correct name, which ran Ok, and shut down the machine.
> 
> This morning I turned on the box, did an 'xm list', and found what 
> appeared to be a zombie with the new VM name (no ID, no status; just a 
> name). So, I virsh undefined it.

You should 'virsh destroy' zombies, rather than 'virsh undefine'. 'Destroy'
will forcably kill the VM. 'Undefine' merely removes its config file.

> This seems to have been a big mistake. I then discovered that 
> virt-install doesn't create a config file, and there was nothing in 
> /var/lib/xend/domains, presumably because of the undefine (none of this 
> is documented in Fedora7VirtQuickStart, by the way).

virt-install *does* create a config file. You explicitly deleted the config
file by running 'virsh undefine'. The config files are managed by XenD in
/var/lib/xend/domains, /etc/xen is a legacy location no longer used by default
from Xen 3.0.4 and later.

> How do I get my VM back? Is there some way to get the XML config back? 

Check /root/.virt-install/virt-install.log  where you may well have a copy
of the config file in the logs

> If not, is my only option to manually make an /etc/xen config file? 
> There's a little bit of information in xend.log which I could use for 
> the config file.

Re-run  'virt-install' with the same parameters and pointing to your
existing installed disk image. When the installer pops up, instead of
going through the install process, simply 'virsh destroy' to shutdown
the guest VM. You should now have a config file for the guest again.

> Finally, I'm (very) confused about what exactly is 'Xen' and what 
> exactly is 'Fedora'. You seem to have done various things which I'm 
> guessing are Fedora-specific, but which don't seem to be documented 
> (I've had a lot of trouble with /etc/inittab, for example). Is this 
> documented somewhere? And am I going to run into any problems if I 
> convert a virt-install domain back to plain-old-Xen?

There's no difference between a VM created by 'virt-install' and one created
another way. If you use the same VM config params in both approaches you'll
end up with the same VM.

libvirt & virt-install ultimately talk to the same underlying XenD APIs
as any other tool. libvirt is simply exposing an API / toolset which is
not Xen-specific / portable to virtualization like QEMU, KVM, OpenVZ etc

Regards,
Dan.
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