Can you run the server with start_urbackup_server --no_daemon and have a look at the console output? Could be a problem related with setuid (urbackup_snapshot_helper cannot be elevated to root from user urbackup).
Just so I can learn more about btrfs (old to linux, new to btrfs), would this be a correct output if btrfs snapshots is working properly?
root@UrBackup2:/mnt/backup# btrfs subvolume list -p .
ID 365 gen 4127 parent 5 top level 5 path 8T44DS1/151211-1508
ID 427 gen 4127 parent 5 top level 5 path 8T44DS1/151211-1604
ID 428 gen 4127 parent 5 top level 5 path 8T44DS1/151211-1606
ID 493 gen 4127 parent 5 top level 5 path 8T44DS1/151212-0152
ID 737 gen 4127 parent 5 top level 5 path 8T44DS1/151212-0653
ID 738 gen 4127 parent 5 top level 5 path 8T44DS1/151212-1154
ID 739 gen 4127 parent 5 top level 5 path 8T44DS1/151212-1655
ID 740 gen 4127 parent 5 top level 5 path 8T44DS1/151212-2156
ID 769 gen 4127 parent 5 top level 5 path 8T44DS1/151213-0546
ID 770 gen 4127 parent 5 top level 5 path 8T44DS1/151213-1047
ID 771 gen 4127 parent 5 top level 5 path 8T44DS1/151213-1548
ID 772 gen 4127 parent 5 top level 5 path 8T44DS1/151213-2049
ID 773 gen 4127 parent 5 top level 5 path 8T44DS1/151214-0733
ID 812 gen 4127 parent 5 top level 5 path 8T44DS1/151214-1613
ID 815 gen 4127 parent 5 top level 5 path 8T44DS1/151215-0803
ID 863 gen 4158 parent 5 top level 5 path 8T44DS1/151216-0833
ID 904 gen 4167 parent 5 top level 5 path 8T44DS1/151217-1515
Sorry, that I didn’t answer @uroni. I removed all backups and configs and reinstalled the server and it just worked… BTRFS snapshots are being created. So no problem anymore, but I really dont’t know what went wrong in the first place.
@Flatlinebb: yes looks good the output. You can just browse the snapshots as a normal filesystem and check if everything is there.