setup journaling for root partition

[s m]

hello everybody

i want to setup a journal partition for my root partition. but i do not
know how to do that. in FreeBSD handbook, it is done in single user mode,
unmount the desired partition and assign the journal partition to it. i
test this procedure and it is done for /usr partition but for root
partition, it can not be unmount in single user mode.

i try to do it in fixiit mode, but i can not load gjournal.

do i use gpart to partitioning my system and enable journaling for root
partition? isn't there any way to setup journaling for my existing root
partition? which command should be used (or is better to used) to enable
journaling? tunefs, gjournal or newfs?

please help me to setup a journal partition for my root.
thanks in advance
SAM