It's pretty common to run FreeBSD jails with old userspace (say, 8.0) on top of up to date FreeBSD kernel (say, 12.1). This works because to the stable syscall

It's pretty common to run FreeBSD jails with old userspace (say, 8.0) on top of up to date FreeBSD kernel (say, 12.1). This works because to the stable syscall interface.