Backup LXC to NAS NFS share Fails

[cliver]

I have an NFS share setup on my Asustor NAS which I want to hold my backups.
I am having trouble getting them all to work.
I have 2 LXC's currently, Lyrion Music Server and Nginx proxy manager plus one VM, HAOS.
Backing up the Lyrion container works without error but backing up the Nginx container gives the following:

INFO: starting new backup job: vzdump 100 --notification-mode notification-system --node proxmoxve --notes-template '{{guestname}}' --remove 0 --mode snapshot --storage Proxmox_Nas_Share --compress zstd
INFO: Starting Backup of VM 100 (lxc)
INFO: Backup started at 2026-09-19 14:06:30
INFO: status = running
INFO: CT Name: nginxproxymanager
INFO: including mount point rootfs ('/') in backup
INFO: mode failure - some volumes do not support snapshots
INFO: trying 'suspend' mode instead
INFO: backup mode: suspend
INFO: ionice priority: 7
INFO: CT Name: nginxproxymanager
INFO: including mount point rootfs ('/') in backup
INFO: temporary directory is on NFS, disabling xattr and acl support, consider configuring a local tmpdir via /etc/vzdump.conf
INFO: starting first sync /proc/1416/root/ to /mnt/pve/Proxmox_Nas_Share/dump/vzdump-lxc-100-2026_09_19-14_06_30.tmp
INFO: first sync finished - transferred 3.94G bytes in 1424s
INFO: suspending guest
INFO: starting final sync /proc/1416/root/ to /mnt/pve/Proxmox_Nas_Share/dump/vzdump-lxc-100-2026_09_19-14_06_30.tmp
INFO: final sync finished - transferred 19.00M bytes in 55s
INFO: resuming guest
INFO: guest is online again after 55 seconds
INFO: creating vzdump archive '/mnt/pve/Proxmox_Nas_Share/dump/vzdump-lxc-100-2026_09_19-14_06_30.tar.zst'
INFO: tar: ./var/spool/postfix/hold: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/public: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/incoming: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/defer: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/trace: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/bounce: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/private: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/active: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/saved: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/maildrop: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/corrupt: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/flush: Cannot open: Permission denied
INFO: tar: ./var/spool/postfix/deferred: Cannot open: Permission denied
INFO: tar: ./var/lib/apt/lists/partial: Cannot open: Permission denied
INFO: tar: ./var/lib/postfix/master.lock: Cannot open: Permission denied
INFO: tar: ./var/cache/apt/archives/partial: Cannot open: Permission denied
INFO: Total bytes written: 4259594240 (4.0GiB, 7.5MiB/s)
INFO: tar: Exiting with failure status due to previous errors
ERROR: Backup of VM 100 failed - command 'set -o pipefail && lxc-usernsexec -m u:0:100000:65536 -m g:0:100000:65536 -- tar cpf - --totals --one-file-system -p --sparse --numeric-owner --acls --xattrs '--xattrs-include=user.*' '--xattrs-include=security.capability' '--warning=no-file-ignored' '--warning=no-xattr-write' --one-file-system '--warning=no-file-ignored' '--directory=/mnt/pve/Proxmox_Nas_Share/dump/vzdump-lxc-100-2026_09_19-14_06_30.tmp' ./etc/vzdump/pct.conf ./etc/vzdump/pct.fw '--directory=/mnt/pve/Proxmox_Nas_Share/dump/vzdump-lxc-100-2026_09_19-14_06_30.tmp' --no-anchored '--exclude=lost+found' --anchored '--exclude=./tmp/?*' '--exclude=./var/tmp/?*' '--exclude=./var/run/?*.pid' . | zstd '--threads=1' >/mnt/pve/Proxmox_Nas_Share/dump/vzdump-lxc-100-2026_09_19-14_06_30.tar.dat' failed: exit code 2
INFO: Failed at 2026-09-19 14:45:34
INFO: Backup job finished with errors
INFO: notified via target `mail-to-root`
TASK ERROR: job errors

I'm struggling to get my mind around what the problem is.
I assume I have the share permissions set up OK because one CT backup succeeds?
I assume this won't stop it working but would speed it up and allow snapshots? Not sure how that would work in practice.
The main issue, as I understand it is all the Permission denied INFO reports near the end? Are they referring to ./var/*** in the tar file on the NAS? If so what permissions am I missing?
Any help appreciated.

 

[Max Carrara]

Hmm, interesting — what do the logs of your other backup job say? Just for comparison. The directories that are listed in your logs exist on my container as well, but are backed up without any issues. Also, 7.5MiB/s seems quite slow ... especially since you're only writing 4.0GiB in total. The initial sync also seems to have taken almost 24 minutes.

 

[cliver]

Hmm, interesting — what do the logs of your other backup job say? Just for comparison. The directories that are listed in your logs exist on my container as well, but are backed up without any issues. Also, 7.5MiB/s seems quite slow ... especially since you're only writing 4.0GiB in total. The initial sync also seems to have taken almost 24 minutes.

Hi Max, Thanks for the reply. Interestingly, for unrelated reasons, I have just rebuilt my proxmox node on different hardware and restored from backups created locally and copied out to the NAS and all seems to be working now. Not sure what the differences are as the hardware is similar though not exact duplicates. I'll do some more testing when I get time. Plus I do need to look at my NAS speeds .
Regards
Clive

 

[Max Carrara]

Oh, okay! That's very interesting. I'm glad it works now, at least. Hope it stays that way!