can i just upgrade the 8.1 kernel ?

[b. f.]

>FreeBSD mybsd.zsoft.com 8.0-RELEASE-p2 FreeBSD 8.0-RELEASE-p2 #0: Wed Jul 14
>15:35:26 CST 2010
>root at mybsd.zsoft.com:/media/G/usr/obj/media/G/usr/src/sys/MYKERNEL  i386
>
>Can i just use the following commands to upgrade to 8.1 kernel ? And does
>the virtualbox-ose still work under 8.1 ?

Check the mailing lists and PRs to see if anyone has had problems. It
probably works.

># csup -g -L 2 -h cvsup.freebsd.org
>/usr/share/examples/cvsup/standard-supfile

I think that this file contains:
*default release=cvs tag=.
which would update /usr/src to 9-CURRENT (-head).  That doesn't sound
like what you want.  Instead, you probably want the stable-supfile in
the same directory instead, which probably has(check this yourself):
*default release=cvs tag=RELENG_8
That would update your sources to the latest 8-STABLE, which is a
little in advance of 8.1.  Or you could change the tag to RELENG_8_1,
to be more conservative.  That would be 8.1+critical updates, if any.

># cd /usr/src
># make buildkernel KERNCONF=MYKERNEL
># make installkernel KERNCONF=MYKERNEL

You probably want to update the rest of the base system as well as the
kernel.  Follow the instructions near the bottom of /usr/src/UPDATING,
something like:

cd /usr/src
make buildworld kernel KERNCONF=MYKERNEL
reboot in single user
fsck -p /
mount -u /
mount -a
adjkerntz -i
mergemaster -p
cd /usr/src
make installworld
make delete-old delete-old-libs
mergemaster -i
reboot

b.