Made backup of /etc:
# cp -Rp /etc /etc.old
Run mergmaster in pre-buildworld mode. This compares only files known to be essential to the success of buildworld and installworld, including /etc/make.conf.
# cd /usr/src/usr.sbin/mergemaster # ./mergemaster.sh -p
If you have included variables in /ect/make.conf that are not part of /etc/defaults/make.conf you may see harmless messages.