> It lasts for a couple of years

Then it's not Let's Encrypt - as per their FAQ:

"Our certificates are valid for 90 days. You can read about why here.

There is no way to adjust this, there are no exceptions. We recommend automatically renewing your certificates every 60 days."

However it could be you're using Certbot with another service - since the ISRG aren't idiots, they created a standardised protocol (ACME), and there are several other CAs that use it now.

It's definitely Let's Encrypt with Certbot because I went and had a look through my emails when I saw this thread. But I can't even remember installing it all. And ACME does ring a bell. I suppose I should go and check before it all stops working. I do vaguely remember that there's a limit of around a couple of years before I have to reapply to use it - presumably as opposed to expiry.

Anyway, my more immediate concern is whether to update to the latest version of OwnCloud since they withdrew their nice simple upgrade script.

" a piece of piss "

Not on my server (there are no certbot packages for it). The Let's Encrypt manual route is far, far simpler.

Chrome Canary with Bitdefender chucking up dark warnings, but letting me through all the same.