On Tue, 30 Jul 2019 11:35:45 +0100 Daniel P. Berrangé <berrange@xxxxxxxxxx> wrote: > On Mon, Jul 29, 2019 at 02:04:14PM +0200, Stephan von Krawczynski wrote: > > Hello, > > > > is there some immanent code in libvirt that forces UID/GID of the libvirt > > standard user to be the same on two boxes migrating qemu vms against each > > other? > > The migration itself uses root obviously (password is requested). But if a > > vm xml does not contain any definition regarding UID/GID what else could > > prevent this from working? > > > > I believe I ran into such a problem trying to migrate and ending up in an > > error, a vm still working on original host but its fs (netfs pool > > (nfs/raw)) being switched to read-only... > > When migrating a VM whose image is hosted on NFS, you have 2 QEMU processes > which both need to be able to open the same image file at the same time. > QEMU runs as an unprivileged user normally, and so the disk images get > chowned to this unprivileged user by libvirt when QEMU is started. If the > QEMU on the target host is given a UID/GID that's different from the QEMU > on the source host, then the target QEMU will likely have problems opening > the image. > > Basically when using shared FS storage, the rule is to have all your hosts > configured in the same way from libvirt's POV. > > Regards, > Daniel Hello Daniel, thank you for the short explanation. The key words are "both need to be able to open the same image file at the same time". I would not have expected that. I thought qemu 1 will close and exit, and then qemu 2 will open the image, which means he can change the uid/gid right before - just as in normal operation. Is this the reason why my failing try leaves me with a read-only fs on the guest? Which I would see as a bug, not? Turning it read-only is possibly the only way to not corrupt the fs image if two qemus have it open simultaneously. -- Regards, Stephan -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
