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_do_I_edit_a_VM.27s_XML_config.3F 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. -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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