LXC backups are failing when the container includes snaps

[dirhea]

Just looking into the integrated Proxmox backup on my host and it seems LXC backups are working fine but when the LXC includes a snap then it is failing like so:

ERROR: rsync: [sender] readlink_stat("/proc/3691699/root/snap/xxx/2411") failed: Permission denied (13)
ERROR: rsync: [sender] readlink_stat("/proc/3691699/root/snap/xxx/523") failed: Permission denied (13)
ERROR: rsync: [sender] readlink_stat("/proc/3691699/root/snap/xxx/26382") failed: Permission denied (13)
 ERROR: rsync: [sender] readlink_stat("/proc/3691699/root/snap/xxx/26865") failed: Permission denied (13)

The other LXCs are backing up fine except this one but the others don't have snaps on them so I think that is probably the cause.

I have tried to set the tmp directory in /etc/vzdump.conf to /tmp but this didn't seem to make any difference, I think rsync is failing to read the snap which is why it is failing.

Any ideas how to resolve this?

 

[leesteken]

Use a Debian container instead of Ubuntu? I have Nextcloud as a snap in a Ubuntu (24.04) container, which does not give any errors during a backup (to PBS). Maybe it's specific to your snap-based app xxx? Have you tried Stop instead of Snapshot mode (as a work-around)?
It's a bit weird that /proc is being backed up. How are you backing up and what versions of Proxmox VE, BS or backup-client are you using? You could exclude /proc in a .pxarexclude file (as a work-around), which does not only work for backup-client but also backups from PVE.

 

[dirhea]

They're different snaps (including snapd itself) but they failed all for the same reason. So I redacted the snap names...
This is the latest version of Proxmox using the backup tool built into the system. So just selecting the LXC's from the list and then going ahead on the default settings.

If I try the stop mode as you suggest does that mean the LXC needs to be stopped to run the backup?

Surely there's some sort of permission issue going on here with the backup routine not being able to read the folder?

 

[leesteken]

This is the latest version of Proxmox using the backup tool built into the system. So just selecting the LXC's from the list and then going ahead on the default settings.

So you are backing up to a file on a directory storage and not to PBS?

If I try the stop mode as you suggest does that mean the LXC needs to be stopped to run the backup?

Yes. Maybe not what you want but it would be an interesting data point to try (once).

Surely there's some sort of permission issue going on here with the backup routine not being able to read the folder?

Maybe check the file owner, group and permission from the Proxmox host? My unprivileged container with snap when backed up from PVE to PBS does not contain any files from /proc.

 

[dirhea]

Stopping it does work. In fact looking at how /proc/ works it seems a bit strange that Proxmox is trying to back it up at all. I have the VMs backed up externally through another tool and it's all excluded there, and it isn't where snap should be storing anything meaningful, but I can't see how to exclude it... which is probably the meaningful answer

This is just the backup feature built into proxmox itself, i.e. the one where you click on datacentre then go to backup down the side. It doesn't seem to matter where it's set to back up - I have the others going to a file on a network share which is mounted into proxmox, but it doesn't matter whether or not it uses local storage.

Where are the exclusion settings?

 

[leesteken]

In fact looking at how /proc/ works it seems a bit strange that Proxmox is trying to back it up at all.

That is what I said here.

but I can't see how to exclude it... which is probably the meaningful answer

As I said here also, you might be able to exclude it (even though I cannot explain why it is not excluded automatically). Maybe someone else knows?

This is just the backup feature built into proxmox itself, i.e. the one where you click on datacentre then go to backup down the side. It doesn't seem to matter where it's set to back up - I have the others going to a file on a network share which is mounted into proxmox, but it doesn't matter whether or not it uses local storage.

The "backup feature build into proxmox itself" can also backup to PBS. I agree that the actual type of the destination of the directory storage does not matter, but PBS might be different.

Where are the exclusion settings?

I don't know if it works when the backup destination is not PBS, but the manual section I linked to (the colored and clickable texts in my replies) in the reply I referred to already twice tells you to create an exclusion file inside the container, for example in the root of the container (to exclude /proc).