Nextcloud Error: Could not generate a preview of this file

The full error looks like:

I have a picture folder which is 19GB, not all the images in this folder have this problem, but most of the images when clicked to preview come up with this error message.
It seems to only be this one folder.

My setup:
Nextcloud: 13.0.4
PHP: 7.1
Apache 2.4
Ubuntu 16.04

I am running this on AWS using the free tier option, it has 1 vcore and 1GB of RAM, is it because the spec is so low?

Also, in that same folder, most of the thumbnails don’t loads for images either? Other folders with less images load their thumbnail…

There is a reason we show a template when opening a new topic. Please take a look into your log files, if you are short on memory, it should show up somewhere (Nextcloud-log or webserver-log).

Okay, sorry this was my first problem with NC.

Where might I find Nextcloud-log? Also would it make any difference that my main storage is AWS S3? And that the VPS only has 30GB of storage?


when preview are not generated, usually, this means your picture is:

  • in a unknown format
  • use bad names format
  • is not readable by nextcloud


  • store in a directory/location without the good right

Nothing to do with total size of the storage, unless the picture is larger ( thank you spock, logic is respected :rofl:

Well, I did look in the logs for NC and I do have logs for out of memory warnings and how the connection for the mysql server has “gone away”. So I think it might be to do with the small amount of RAM (1GB).

Minimum ram requirement is supposed to be 512 Mo, witch is the lowest of the lowest.

A normal linux debian/ubuntu server is already in need of a 512 mo … added to the nextcloud minimum 512 mo, your ram is already max-out

I have 32GB of ram on my server, and i feel low …

And if you are low, you have to manage the services properly by giving them the right amount of RAM (not too much, so there is nothing left for other important processes, and not too little). There are scripts to manage the right amount of cache for mysql (tuning-primer, mysqltuner) and the rest you can tune by the general amount of memory and also the number of child processes.