Well, that’s the thing: user openhab is owner of the folder and all files. And it can write into the file once it has been created, that’s why I’m unclear if this has anything to do with linux user rights. There are a couple of similar entries if you search the community with the term “Failed to open rrd4j database”, like this one or this one. But there seems never have been a root cause identified as far as I can tell.
me@namibia /var/lib/openhab/persistence/rrd4j $ ls -la
insgesamt 88
drwxr-xr-x 3 openhab openhab 4096 14. Jan 23:02 .
drwxr-xr-x 5 openhab openhab 4096 3. Jan 19:09 ..
-rw-r--r-- 1 openhab openhab 9444 17. Jan 18:17 RH_Aussen.rrd
-rw-r--r-- 1 openhab openhab 9444 17. Jan 18:17 RH_Innen.rrd
-rw-r--r-- 1 openhab openhab 9444 17. Jan 18:17 RH_Keller.rrd
-rwxr-xr-x 1 openhab openhab 28280 17. Jan 18:17 Temp_Aussen.rrd
-rw-r--r-- 1 openhab openhab 9444 17. Jan 18:17 Ventilator_Bad_RH.rrd