Questions about Jail

[perryh at pluto.rain.com]

Fbsd8 <fbsd8 at a1poweruser.com> wrote:

> In most cases your jail environment will function ok as long as
> its the same base release level. Example, host=8.0 jail1=8.1 and
> jail2=8.2

IIUC, a better example would be host=8.2, jail1=8.1 and jail2=8.0.
A point release is not supposed to make any incompatible changes to
the kernel ABI, but it might add new interfaces not present in the
older kernel.

> But host=8.2 and jail1=9.0 will have unknown reliability.

I would say it is only an accident if (jail major > kernel major)
works, because the KABI will likely have changed between N.x and
(N+1).x.  However, host=9.0, jail1=8.x should work if the host
kernel includes the COMPAT_FREEBSD8 option.

> Technically there is no checks stopping someone from doing this
> and from the outside all will look correct, but it will fail and
> you may lose both the host and jail.

You may indeed lose the jail, but if _anything_ done in the jail is
able to corrupt the host there is by definition a bug in the host's
jail support.