Problems establishing btrfs-snapshot sync: wrong permissions?

Hi there,
after two years of using Nexcloutpi and btrfs-snapshot sync nearly without trouble I can’t get btrfs-sync to work this time. Installation of Nextcloudpi has been renewed, so I had to configure sync on nextcloud server again (running on a Zbox now). The configuration on backup-server hasn’t changed so far.

This is not the first time I have done the steps getting to work, but now I get following issues:

  1. Starting ncp-snapshot-sync on ncp-web-panel shows:
[ nc-snapshot-sync ] (Thu Mar 16 20:02:15 CET 2023)
Host key verification failed.
SSH non-interactive not properly configured

That’s weired because I’ve created a new rsa key and ssh auto login is working when I connect to my backup server via ssh. No password is needed.

  1. Starting ncp-snapshot-sync manually with
btrfs-sync --verbose /path/to/ncp-snapshots/daily_2023-03-15_193402


SSH access error to Do you have passwordless login setup, and adequate permissions for /path/to/backup/ncp-snapshots?

Btrfs-user has root-permissions for /bin/btrfs-sync cause of

btrfs-user ALL=(root:nobody) NOPASSWD:NOEXEC: /bin/btrfs



Permissions on nextcloud-server as well as backup-server for /path/to/ncp-snapshots/daily_2023-03-15_193402 are

drwxr-x— 1 www-data www-data

for parent folder /path/to/ncp-snapshots

drwxr-xr-- 1 btrfs-user sudo

At this point my wisdom is at its end :frowning:
Can someone help me?

Thanks in advance,

My system:
Nextcloud version: 25.0.3
NextcloudPi Versoin: 1.51.0
Operating system and version: Debian 10.2.1-6
Apache or nginx version: ??
PHP version: 8.1.15