We have set up automatic backups and have also moved /var/discourse/shared/standalone/uploads and /var/discourse/shared/standalone/backups according to this guide to an external drive, i.e. we have the following app.yml config:
Which directory do you mean? The one that contains the backup (/path/to/external/backups/default) already is writable by everybody (see output of ls -la above).
gzip creates a second file and removes the uncompressed file upon completion. This means that you need to have at least 327 MB of disk space available. Error messages might be obscured due to the fact that this is an external drive. Theory: you might be running out of disk space?
Notably, a manual backup succeeded after I chose “Yes (do not include uploads)” – log here. So the failure might indeed be related to the amount of data compressed.
I then moved the backups to the internal drive again, and now manual backups also work with uploads included – log here.
It seems the failure is specific to our gocryptfs / SAMBA setup. Still, if anybody has ideas to investigate this further, I’m happy to hear them. Like, what exactly makes gzip say Operation not permitted.