Unble to upgrade ubuntu-core 16 to anything

So trying to upgrade/ remodel the Nextcloud appliance from core16 to core18 and then hopefully to core20 and core22.

But nothing seems to work. When trying to apply a new model.

snap remodel nextcloud-core18-pi-armhf.model 
error: cannot remodel: cannot remodel device: cannot remodel from core to bases yet

The same happens with any generic pi-armhf model as well.

How to get past this ?

I dont think you can … re-modeling is a feature that was only added with UbuntuCore 20 …

Then why is there a nextcloud-core18-pi-armhf.model under the appliances folder of


To build an Ubuntu Core 18 image I suppose…

Recently updated from RPi3 to RPi4 for Nextcloud.

So a fresh install of Ubuntu core on RPi4 gave me:

Name       Version         Rev    Tracking       Publisher   Notes
core18     20230901        2800   latest/stable  canonical✓  base
core22     20230801        867    latest/stable  canonical✓  base
pi         22-2            132    22/stable      canonical✓  gadget
pi-kernel  5.15.0-1042.45  706    22/stable      canonical✓  kernel
snapd      2.60.4          20298  latest/stable  canonical✓  snapd

Then, I installed nextcloud (26.0.6 due to the issues with updating with the small memory on RPi3).

nextcloud  26.0.6snap1     37838  26/stable      nextcloud✓  -

There was no /var/lib/snapd/snapshots, thus I first did a snap save pi then it got created.

A big snapshot-zip had been transferred between the two different disks I use for RPi3 and RPi4. The restore went fine with snap restore <snapshot-id>.