From: "Eric Blake" <eblake(a)redhat.com&gt; To: "Andrew Martin" <amartin(a)xes-inc.com&gt;, libvirt-users(a)redhat.com Sent: Tuesday, April 14, 2015 10:26:50 AM Subject: Re: [libvirt-users] Update on-disk XML after virsh snapshot-create-as On 04/14/2015 09:17 AM, Andrew Martin wrote: > Hello, > > I am using "virsh snapshot-create-as" to create external snapshots of > running > VMs using libvirt 1.0.2 on Ubuntu 12.04 and libvirt 1.2.2 on Ubuntu 14.04. > This > works well for creating the snapshots, but I notice that the on-disk XML > file > in /etc/libvirt/qemu is not updated with the new disk image file after the > snapshot is created. This appears to be very similar to > https://bugs.launchpad.net/ubuntu/+source/libvirt/+bug/1403841, but occurs > on > both 12.04 and 14.04 so I am not sure it is the same bug. There have been some bug fixes in newer libvirt; for example, commit 9f97485 (v1.2.12) is relevant. I'm not sure why your vendor is not backporting these fixes to the build shipped in Ubuntu, but you can manually run a newer libvirt to work around the problem.

> > This presents a problem if the virtual machine host is suddenly powered off > since a subsequent boot will find the VM using an older image file to boot > rather than the most recent snapshot. Is it safe for me to use an external > wrapper script that does the following to ensure the on-disk XML is > up-to-date: > virsh snapshot-create-as .... > virsh dumpxml > /etc/libvirt/qemu/<domain>.xml No. That is not safe. > > Is it safe for me to overwrite the contents of > /etc/libvirt/qemu/<domain>.xml > manually while the VM is running? Not at all. http://wiki.libvirt.org/page/FAQ#Where_are_VM_config_files_stored.3F_How_... Instead, if you are still suffering from a build of libvirt that fails to update the files in /etc when taking a snapshot, do some other action that DOES update /etc (such as changing the domain description), or at a bare minimum use 'virsh define' instead of manually writing into /etc yourself.