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Sorry to hear you’re facing problems 
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Or for longer, use three backticks above and below the code snippet:
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Some or all of the below information will be requested if it isn’t supplied; for fastest response please provide as much as you can 
Nextcloud version (eg, 12.0.2): 17.0.2
Operating system and version (eg, Ubuntu 17.04): arch
Apache or nginx version (eg, Apache 2.4.25): nginx 1.16.1
PHP version (eg, 7.1): 7.3
The issue you are facing:
After an update the nextcloud website invites me to create an admin user etc even though I had been running nextcloud for a while already. It looks like the reason is that my config.php in /etc/webapps/nextcloud/config, which is symlinked from /usr/share/webapps/nextcloud/config is basically empty after now. I can’t tell for sure what caused that, but at least checking the modification times I can tell that the last time config.php was modified is up to 1/2 of a second exactly the time when the update started. Maybe the file has disappeared earlier already and the update just put the stub file there because config.php had already gone, I don’t know. But I don’t know what would have caused the file to disappear if not the update. The ssd where config.php lies has not reported any errors so far.
It looks similar to Nextcloud returns to page "create admin account" after update.
Of course I had been doing backups, but only of /usr/share/webapps/nextcloud, and I hadn’t realized until now that the config folder there is only a symlink, and I configured the update in a way that it preserves symlinks, oh well… I will backup the config files in /etc/ from now on too, had been planning to do that anyways.
Is this the first time you’ve seen this error? (Y/N): Y
Steps to replicate it:
I don’t feel like testing that out.
The output of your Nextcloud log in Admin > Logging:
I don’t know where to find this.
The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):
<?php
$CONFIG = array (
'instanceid' => 'oce7zkjp9x37',
);
The output of your Apache/nginx/system log in /var/log/____:
Is this interesting?
EDIT: Actually I don’t know too much about how nextcloud works, so it might very well be that my assumption that nextcloud doesn’t work because config.php doesn’t seem to contain much is not correct. In any case, help would be much appreciated.
EDIT: Also when trying to turn on maintenance mode it says that nextcloud is not even installed. And that php says it can’t find imagick.