In the continuing adventures of my laptop hard drive failing, I decided that I might as well upgrade to Ubuntu 18.04 on this laptop, seeing as I had to reinstall it all from scratch anyway (the laptop is only for development / testing / experimenting, so I can afford to be more adventurous with it, at it's not actually serving anyone but me on "localhost". Definitely not a production server). There were a few changes from the Ubuntu 16.04 "perfect server" tutorial that I was following, but I was able to work out - from the error messages and looking up what a few packages had been renamed to - how to make it work and get ISPConfig up and running. My issue is, admittedly, cosmetic. But it does mean that the "monitor" page of ISPConfig is rendered useless, as the server is permanently red for "error" when there isn't strictly a problem. To explain, Ubuntu 18.04 comes with some snaps pre-installed (mostly gnome utilities). Snaps use Apparmor. The very first instructions in "perfect server" is to turn off Apparmor. Snapd is therefore uninstalled as it depends on that. The snaps are useless. This is not the end of the world, though, as you can still install the old "apt" versions of these things. On the ISPConfig side of things, snaps create these "loopback" file systems - "/dev/loop0", "/dev/loop1" - mounted onto the "/snap" directory and these are all "squashfs" and have zero bytes available. They're all "100%" usage by design. The problem here is that ISPConfig sees the zero available bytes on these and then flags up the error that the disk is full. But my actual "/" happily has 1.7TB available (2% usage, so still a very long way from "disk full"). So this is not an actual true error. It's just ISPConfig not knowing to just ignore these special snap filesystems, as they're always "100% usage" and that's fine. That's just how they work. Well, if you dev guys have been working on "perfect server" for Ubuntu 18.04 then you might well have spotted this problem. Snaps and how the guide / ISPConfig currently work are, unfortunately, a bit intrinsically incompatible. Snaps use Apparmor. You can't turn off Apparmor without disabling snaps completely (I can live with this for the time being as I never used snaps before, so I can happily continue never using them, but it will cause various issues going forward. Also, the snaps in question are all desktop apps, which a real headless production server wouldn't care about anyway as it wouldn't have a desktop). The problem here, of course, is that because the server is permanently rendered red for "error", then this could well mask a genuine error. Certainly, I can't use "monitor" to spot when packages need updating, as red overrides blue which overrides green. It's cosmetic, granted. It'll function regardless. But it'll be interesting to see the "perfect server" for 18.04 and how it gets around these things.