add path to normal user
 

if a normal user just want to type ifconfig rather than /sbin/ifconfig. How can I do it ?

You can add "/sbin" to the PATH variable:
PATH="/sbin:"$PATH

It will only last for a session so you probably want to put it in a login script for either that user all for all users.

sorry, i also don't understand, can u teach me step by step.
Thanks!!!

in the user's home directory, there should be a file called .bash_profile, which has the PATH defined in it. add what you want to that.

is it nescessary to reboot linux after vi .bash_profile. to take effective ? any other method ?

logout and log back in.

Thank you very much !!!