Nextcloud broke after "no space left on device"

My root partition ran out of space, so I did

rm /var/log/nextcloud.log

(because it was 2GB large). I also added

'loglevel' => 2,

to config.php of nextcloud instance. Last but not least I issued

sudo apt clean

to remove packages from cache on my local node to free some more space on root.

When I tried to login into nextcloud it showed

Es sieht so aus, als ob Du Nextcloud erneut installieren möchtest. Es fehlt jedoch die Datei CAN_INSTALL in Deinem Konfigurationsordner. Bitte erstelle die Datei CAN_INSTALL im Konfigurationsordner um fortzufahren. 


sudo -u www-data php occ status


Nextcloud is not installed - only a limited number of commands are available
  - installed: false
  - version:
  - versionstring: 20.0.5
  - edition:

This was running perfectly fine until space ran out. Has anybody a clue what I could do to repair this instance?