Update to latest stable fails

[chaiuwe]

Hi guys,
I'm currently on 4.0 build 15 2016-10-31 and my System keeps telling me "Update available". When applying the Update the System reboots, says "Upgrading the System" and after a few seconds reboots again without any error message and I'm back on 4.0 build 15 2016-10-31. Two questions:

1. Is there anything I can do about it, besides doing a fresh start?
2. If not, which folders and files should I backup in order to keep my current config when doing a fresh start with latest stable, besides savegames and roms obviously?

Thanks for any help!

edit: found 2 log files:
upgrade.err.log:
mount: mounting /dev/root on / failed: Invalid argument

upgrade.out.log
Thu Jan 1 01:00:02 CET 1970
Upgrading /boot
Thu Jan 1 01:00:04 CET 1970
Thu Jan 1 01:00:04 CET 1970
Upgrading /

[Substring]

@chaiuwe You have a very strange error ... were you using an official recalbox release ?

Still, as we've always strongly suggested to use some external storage, you could read https://github.com/recalbox/recalbox-os/wiki/Use-an-external-usb-storage-device-on-recalbox-(EN)

that's a good way for you to backup easily

[chaiuwe]

Thanks for your fast replay @SUBSTRING! Yes I am using an official release, although if I remember correctly the last update I got was the one saying "yolo" in the changelog which was only live for a couple of hours, so dunno about that...
Thanks for your advise on external storage, gonna look into it! chaiuwe