Re: [libvirt] UID/GID during kvm/qemu migrate

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