"Special Files" with Synology Hyper Backup

[kw-sudo]

Hello,

I back up DietPi daily as a cron job (rsync dietpi-backup) to my Synology DiskStation. Both the backup and the restore work perfectly.

In addition, I back up the NAS with Synology HyperBackup to both USB-HD and cloud storage. In both cases, there are lots of (>1k) warnings in the log regarding an incomplete backup (see example screenshot), which indicate so-called “special files”. Just to be clear, I am only backing up the “offline backup directory” not the "active RasPi".

How can I solve the problem? Path length? Or are the warnings negligible because, for example, HyperBackup “can't do anything” with the files?

RasPi 4
DietPi: 9.10.0
Synology DS716+II
DSM 7.2.2-72806 Update 3

[Joulinar]

not sure if this would be a question for Synology forum. At least from our side we have no inside how Hyperbackup is working. Our backup is nothing than a rsync.

[kw-sudo]

I wasn't sure if it was a “general problem” (Linux/RasPi) or a specific one (Synology).

In the meantime, I took a look at the (database-based, encrypted) Synology backup file. The files transmitted by DietPi (rsync) are complete and identical.

I think the problem lies with Synology. There are files without file extensions in a relevant backup subfolder. The classification probably fails because of these and issues a warning message.

Thanks for sharing your thoughts though. :-)

Regards,
Oliver

[MichaIng]

The missing file extension won't be a problem, as this is very common on Linux/UNIX in general, and thousands of files would be affected then. But the files created by Docker are indeed special at a different level:

root@dietpi:~# ls -l /mnt/dietpi_userdata/docker-data/overlay2/c90d98dbb7d14bd6a91b89b8e13b17e3e2544d64a89c6c2d8e694246b419621b-init/work/work/
total 0
c--------- 1 root root 0, 0 Nov 30  2022 '#1705e5'
root@dietpi:~# ls -l /mnt/dietpi_userdata/docker-data/volumes/backingFsBlockDev
brw------- 1 root root 8, 1 Jan 23 05:25 /mnt/dietpi_userdata/docker-data/volumes/backingFsBlockDev

The first is a characters device, the second a block device. Probably a good idea to check whether those file attributes (the c and the b) remain intact at the Synology.

[kw-sudo]

I've crosschecked the files and they're identical. Thanks for your reply, Micha!

Regards,
Oliver

[MichaIng]

Okay, then I guess the warning is related to the fact that such device files output content they do not contain, so rsync correctly transferred the file type and metadata etc, pointing to the device, but Synology warns that this does not equal the output when reading those files, which comes from the device directly. I'll close the discussion then 🙂.