To do a build world:

1. Check the FreeBSD handbook, on how to do make world. http://www.freebsd.org/ ->Handbook ->Using make world
2. Read /usr/src/UPDATING
3. Backup (script backup-system)
4. Check /etc/make.conf (look at defaults in /etc/default/make.conf)
5. Compare /etc/group with /usr/src/etc/group make sure you have all the groups in the src groups.
6. Optionally: drop into single user mode: shutdown now
7. cd /usr/obj
8. chflags -R noschg *
9. rm -rf *
10. cd /usr/src
11. make buildworld 2>&1 | tee build.log
12. rebuild a GENERIC kernel
13. disable security in /etc/rc.default: kern_secure_level="NO"
    1. cd /usr/src
    2. make buildkernel
    3. make installkernel
14. Optional: rebuild your kernel
    1. cd /usr/src/sys/i386/conf
    2. cp GENERIC to YOUR_KERNEL
    3. vi YOUR_KERNEL, modify appropriatly
    4. /usr/sbin/config YOUR_KERNEL
    5. make depend
    6. cd ../../compile/YOUR_KERNEL
    7. make depend
    8. make
    9. make install
15. reboot to check new kernel
16. make installworld | tee install.log
17. re-enable security options in /etc/rc.default: kern_secure_level="YES"
18. reboot
19. Update /etc,/stand,... with: mergemaster
20. Update /dev with: cd /dev; ./MAKEDEV all
21. reboot: fastboot