On Tue, Jun 17, 2003 at 08:37:37AM -0700, Jeremy C. Reed wrote:
> [...]
> 
> Many times, I have upgraded both at same time. (When using already-made
> binaries when doing an upgrade it is usually always rebooted with new
> kernel and new userland at the same time.)
> 
> One reason to reboot with just new kernel, is if it fails for some
> reason, you can switch back to your old kernel. But if you had new
> userland with old kernel, things like ipf, sysctl, top, ps, et cetera,
> possibly could fail.

The main reason is that the new userland may rely on a new system call, which
the old kernel doesn't understand.

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 24 ans d'experience feront toujours la difference
--