huh, what do you chroot to apt-get/dnf ?

I think you can do that bootstrapping, for example, with debootstrap. (I'm talking by memory)

Absolutely correct. I've got a cross-compile toolchain set up right now that needs Debian (Ubuntu won't do because of different glibc versions in the cross-compile toolchains). I used debootstrap to make a basic Debian Stretch filesystem, chroot into that, and apt-get the remaining pieces and run the build. Works like a charm, no Docker required. And, unlike containers, it's intentionally persistent so future builds go very quickly.

i think you missed my point :)

That's what it seems like :o :P