Re: 4.9-stable to 5.x

>   o can i just do the normal upgrade as described in UPDATING
>     (cvsup, buildworld, kernel, installworld, ...) from 4.9 to
>     5.2RC in one leap?

Recently I updated a new Dell desktop from 4.9 to 5.x by
following /usr/src/UPDATING exactly.  In particular I did:

    mv /usr/src usr/src-4.9
    mv /usr/obj/usr/src /usr/obj/usr/src-4.9
    cvsup
    make buildworld buildkernel installkernel
    cp -p /sys/i386/conf/GENERIC.hints /boot/device.hints
    cd /sys/boot; make install
    reboot
    <hit a key to interrupt the countdown after the kernel is loaded>
    boot -s
    mount -u /
    mount -a
    adjkerntz -i
    mergemaster -p
    rm -rf /usr/include/g++
    make installworld
    mergemaster
    reboot

You can boot your old kernel if the first reboot fails.  You
are pretty much commited to running -current after the
installworld so there is not much point in saving /usr/src as
I did.  But make sure you are aware of -current changes and
where to find things in case something goes wrong.  Having
another freebsd machine nearby would be handy.

ACPI gave me trouble so I just disabled it.  This is one
thing worth knowing.  From the boot loader, and before you do
boot -s, you can do
    set hint.acpi.0.disabled=1
If that solves your problem, don't forget to add
    hint.acpi.0.disabled="1"
in /boot/device.hints.  There are finer grained knobs you
can play with.

>   o is 5.2RC a good compromise choice?

Probably.  If you happen to cvsup -current in the middle of
some major commit or breakage you can be in serious trouble.
At least for upgrade purposes -current seem to be reasonably
stable these days.  Even so, after cvsupping I watched the
-current and cvs lists for a while for signs of problems
before attempting the above.  Just unpack 5.2rc sources in
/usr/src and follow the same sequence.