The /sbin directory is for executables used only by the root user, and only those executables needed to boot and mount /usr and perform system recovery operations. The FSSTND says:
``/sbin typically contains files essential for booting the system in addition to the binaries in /bin. Anything executed after /usr is known to be mounted (when there are no problems) should be placed in /usr/sbin. Local-only system administration binaries should be placed into /usr/local/sbin.''
At a minimum, the following programs should be in /sbin:
clock, getty, init, update, mkswap, swapon, swapoff, halt, reboot, shutdown, fdisk, fsck.*, mkfs.*, lilo, arp, ifconfig, route