When you change users, specifically when you change users to the superuser (aka root) your $PATH variable gets reset. If you look in /etc/profile****(see below) you should see pretty much exactly what happens. In that same file, if you edit the $PATH that is set for root once you have su'd to have /sbin in it, then logout and backin as root, the change should take effect immediately.
So the entry might look like this:
# For root users, ensure that /usr/local/sbin, /usr/sbin, and /sbin are in
# the $PATH. Some means of connection don't add these by default (sshd comes
# to mind).
if [ "`id -u`" = "0" ]; then
echo $PATH | grep /usr/local/sbin 1> /dev/null 2> /dev/null
if [ ! $? = 0 ]; then
After you've added the /sbin to the PATH variable (located at the bottom of the code above).
***: /etc/profile is very important in getting the system running, and keeping it running correctly. Be very careful when you edit this file, and always make a backup of a working copy before making changes.