Backup of LXC failed (/proc/* permission denied)

[PaulePils]

Hello,

I have a weekly backup job running but one of the LXC always fails with the message:

ERROR: Backup of VM 108 failed - command 'set -o pipefail && lxc-usernsexec -m u:0:100000:65536 -m g:0:100000:110 -m g:110:108:1 -m g:119:100119:65417 -- 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=/var/lib/vz/dump/vzdump-lxc-108-2025_08_10-23_55_56.tmp' ./etc/vzdump/pct.conf ./etc/vzdump/pct.fw '--directory=/mnt/vzsnap0' --no-anchored '--exclude=lost+found' --anchored '--exclude=./tmp/?*' '--exclude=./var/tmp/?*' '--exclude=./var/run/?*.pid' ./ | zstd '--threads=1' >/var/lib/vz/dump/vzdump-lxc-108-2025_08_10-23_55_56.tar.dat' failed: exit code 2

The manual start of the job also fails and it doesn't matter if the LXC is running or stopped.
I asked the AI which proposed that the directory

/dev/.lxc/proc

can't be accessed by the backup job and I should exclude this dir.
What is the function of this directory? Any other LXC backups without problems..

How should I proceed? Change permissions of this path? Exclude it?
I want too backup everything before upgrading to Proxmox 9.

My system :

pve-manager/8.4.10/293f4abc4b22fa08 (running kernel: 6.8.8-1-pve)
LXC Ubuntu 24.04 LTS (Unprivileged)
Service running: Jellyfin.Server 10.10.7.0

The LXC config:

arch: amd64
cores: 4
features: nesting=1
hostname: Jellyfin
memory: 4096
mp0: /raid/media,mp=/mnt/media
mp1: /raid/media/books,mp=/mnt/media/books
mp2: /raid/media/movies,mp=/mnt/media/movies
mp3: /raid/media/music,mp=/mnt/media/music
mp4: /raid/media/tv,mp=/mnt/media/tv
net0: name=eth0,bridge=vmbr0,firewall=1,gw=192.168.20.1,hwaddr=BC:24:11:13:051,ip=192.168.20.33/24,ip6=dhcp,tag=20,type=veth
onboot: 1
ostype: ubuntu
rootfs: NVME:vm-108-disk-0,size=8G
startup: order=2
swap: 4096
tags: external
unprivileged: 1
lxc.cgroup2.devices.allow: c 226:0 rwm
lxc.cgroup2.devices.allow: c 226:128 rwm
lxc.cgroup2.devices.allow: c 29:0 rwm
lxc.mount.entry: /dev/dri dev/dri none bind,optional,create=dir
lxc.mount.entry: /dev/dri/card0 dev/dri/card0 none bind,optional,create=file
lxc.mount.entry: /dev/dri/renderD128 dev/renderD128 none bind,optional,create=file
lxc.idmap: u 0 100000 65536
lxc.idmap: g 0 100000 110
lxc.idmap: g 110 108 1
lxc.idmap: g 119 100119 65417