Fixing Proxmox VE NFS Permission Issues with LXC Backups

This is a common issue with NFS backups for unprivileged LXC containers in Proxmox VE.

To properly handle user mapping we must apply the following config:

Using Proxmox’s Backup User Mapping #

Proxmox usually uses UIDs starting from 100000 for unprivileged containers.

1. Check Proxmox container mappings:

pct config <CTID> | grep uid

2. Adjust NFS exports accordingly:

We need to map to the specific UID/GID range used by the containers, for most setups do as follows (replace the path with your NFS path).

/path/to/backup/storage proxmox-host-ip(rw,sync,no_subtree_check,all_squash,anonuid=100000,anongid=100000)

Then we apply the permissions:

sudo chown -R 100000:100000 /path/to/backup/storage
sudo chmod -R 750 /path/to/backup/storage

Testing #

After making changes:

1. Export the NFS share: sudo exportfs -arv
2. Restart NFS services if needed (probably not)
3. Test your backup from Proxmox VE

The all_squash with specific UID/GID mapping should now let you make Proxmox LXC backups correctly.

Useful Links #

• https://forum.proxmox.com/threads/tmp-cannot-open-permission-denied.87730/#post-441028