Source upgrade from 5.5 to 6.X not safe?

[Clint Olsen]

On Nov 04, Robert Watson wrote:
> When I upgrade a remote systems, I'll actually almost always run a few
> days with the new kernel and the old user space to make sure everything
> has settled nicely before doing the user space upgrade, which is harder
> to revert. Reverting to an old kernel is easy, and leaving the door open
> is likewise easy -- as long as you don't installworld.

This is sort of what I was hoping to try, but alas I crashed and burned
before I could even get the new kernel up and running.  I never answered
another question posed, and that was whether or not I rebooted in
single-user mode - I did not.  I also did not install the kernel while in
single-user mode because, well, I'm the only user :) Your comment seemed to
imply that it can be a safe operation to reboot and run the machine
regularly after make installkernel.  Am I reading that correctly?

In general, is it possible that the installkernel did /not/ complete
correctly before I shut down?  Is it ever possible that the machine could
get put into an indeterminate state when doing installkernel on a running
machine?  HP-UX used to behave horribly when a binary got clobbered for a
process that was running, but I have no idea how FreeBSD copes with
changing disk images of a running process.

Thanks,

-Clint