Exits with error sync keybase.leveldb: operation not supported

```
>keybase service 1
▶ INFO Service#Run() exiting with error sync /home/ojf/.local/share/keybase/keybase.leveldb: operation not supported (code 0) [tags:SVC=1vz_BEyn9Acv]
▶ ERROR sync /home/ojf/.local/share/keybase/keybase.leveldb: operation not supported
```

I suspect it might be the real error behind `keybase.service` not starting either, with nothing logged.

I think it's 'not supported' because `/home/ojf` is a FUSE mountpoint? Though having said that, `sync --file-system ` works fine; it's `sync --data ` that doesn't.

Start with the keybase service output and compare the mentioned sync --file-system and sync --data commands on the FUSE-mounted path. Done means determining whether the unsupported sync operation explains the service startup failure and resolving or clearly documenting that failure path.

Written by the indexing model from the issue text.