Enable Temp-Dir in `/etc/vzdump.conf` See * https://www.reddit.com/r/Proxmox/comments/9ucz3o/lxc_unprivileged_backup_task_failing/ * https://forum.proxmox.com/threads/can-not-backup-lxc-unprivileged.71878/#post-321844 * https://blog.doussan.info/posts/container-backup-permission-denied-nfs/