ChimerOS (ky-mer OS)!

It’s always there, even before anything is mounted. You just overlay a filesystem over it during boot.

I’ve seen million-dollar homes that don’t do this either.

If your hot water starts to smell like sulphur, that can also be a sign. Especially if it’s worse when you don’t run it for a day or two.

I made it a few years before I learned it. When I was a kid we hand-washed, and it took a few years of renting before I caught on - not because of any labels or the like, but because of my troubleshooting a smell.

It’s not obvious what it is if you don’t already know about it, and if you don’t install it yourself…

It’s absurd that building codes don’t require some sort of inspection or access to the vent if it’s not a simple straight-through-the-wall affair.