I found that backing up an unprivileged LXC container on Proxmox to an NFS share can fail with a permission denied error when the backup process tries to create a temporary file on the remote share. The fix is to edit /etc/vzdump.conf on my Proxmox node and set tmpdir to /tmp, so the temporary file is built locally before being copied to the share...
My Proxmox backup of an unprivileged LXC container to an NFS share failed with tar permission errors, even though privileged container backups to the same share worked. Testing with throwaway containers, I traced the problem to vzdump’s temp directory living on the NFS mount, and setting tmpdir to /tmp in /etc/vzdump.conf fixed it. I walk through the error logs and include some skepticism about the common forum explanation...
