Welcome to PhotoStructure, @naelam ! Apologies that things didn’t just work right out of the box.
The official docker template suggests using the :stable tag. There was a bug in the last github actions builder that pushed the latest v2.1.0-alpha.7 build to the :latest tag (that I just fixed a couple days ago).
So–if you pulled :latest, you’re running the alpha build right now. That build is what I’m running personally, but you may find issues with it (see this post for details).
In any event, it looks like SQLite can’t write to your /ps/tmp directory. You’ve either got a permissions issue, or your library isn’t on a local disk.
If your /ps/library is on a local hard drive or SSD, add this environment variable to your template: PS_FORCE_LOCAL_DB_REPLICA=false.
More details are here: What’s PS_FORCE_LOCAL_DB_REPLICA?
As far as permissions issues, check out the PUID/PGID docs here.
Finally, this post may have some tips for setting up your UnRAID box (especially the cache): Tkohhh’s recommended Unraid setup