Add /usr/local/sbin to the PATH of a user

The easiest way is to add this line to your user's ~/.bashrc file:

export PATH=$PATH:/usr/local/sbin

Bear in mind that /sbin/, /usr/sbin and /usr/local/sbin are not in normal users' $PATHs by default because these directories tend to contain "dangerous" executables. Things like fdisk or deluser that need administrative privileges and can harm your computer. They should be in root's path by default and you need to be root to run them anyway, so it migh be a good idea not to add them to a normal user's $PATH.

Add the following to the end of the .bashrc of the user:

export PATH=/usr/local/sbin:$PATH