Yeah but I mean you still have to set up the sandbox rules and maintain them and the tools if you want a user-friendly sandbox or a nice GUI to manage it.

>For example that "namespace-sandbox" is standard in Plan9/9front...without any additional software, just the filesystem and 9p.

This is what I mean, Plan9 style mount namespaces are also available in Linux and are preferable to SELinux for containers and sandboxes because they're actually simpler and less trouble.