1. Preparation:
(1)setup NFS server, and a file to save to.
# cat /etc/exports
/test/squash *(rw,async,root_squash)
# systemctl restart nfs-server
# touch /test/squash/save
# chown 107:107 /test/squash/save
# chmod 664 /test/squash/save
(2)# mount $NFS_ip:/test/squash /mnt
# ls -l /mnt/save
-rw-rw-r--. 1 qemu qemu 0 May 17 03:00 /mnt/save
(3)# vi /etc/libvirt/qemu.conf
dynamic_ownership = 0
# systemctl restart virtqemud
(4)change disk image owner to be qemu:qemu
 
2. start vm
# virsh start avocado-vt-vm1
Domain 'avocado-vt-vm1' started


3. try to save to nfs target file
# virsh save avocado-vt-vm1 /mnt/save
error: Failed to save domain 'avocado-vt-vm1' to /mnt/save
error: Error from child process creating '/mnt/save': Unknown error 255


4. check file permission again:
# ls -l /mnt/save
-rw-rw----. 1 qemu qemu 0 May 17 03:53 /mnt/save