I'd really like to try this, but building it is impossible. C++ is such a pain to build with the "`make`; hunt for the dependency that failed; `apt-get install whatever-dev`; goto make" loop...

Please release binaries if you're making a utility :(

What distro are you using? The only two dependencies are libacl and libmount. I'm trying to figure out which distros don't include these by default, and if the libraries are really missing, or if it's just the pkgconf ".pc" files. In the former case I should document the dependencies. In the latter case I should maybe switch from PKG_CHECK_MODULES to old-fashioned autoconf.

I'm using Ubuntu, I gave up when it failed on something about "print".

https://github.com/jrz/container-shell

It does something very simple, and it’s a POSIX shell script. Works on Linux and macOS. Uses docker to sandbox using bind mount

Yeah but it doesn't COW anything else, and Docker is a bit heavy for this.