@stux let me see:
I followed the documentation (https://docs.joinmastodon.org/admin/elasticsearch/) up to security, which refers to the ES page (https://www.elastic.co/guide/en/elasticsearch/reference/7.17/security-minimal-setup.html) which is where I get stuck.

More concretely I get stuck at "Create passwords for built-in users" which seems simple enough but doesn't work. The command doesn't run as root (for probably obvious security reasons), but also not as a local user, leading me to a 'permission denied'.

So, I'm just missing a step along the way, but for the life of me...