How to set permanent alias
 

Hi friends,

I want to set permanent alias for ls -lX and ls -la

I use

alias lx="ls -lX" and
alias la="ls -la"

The problem is when I su to root and get back to the user I use, the alias become unset or it is cleared. I want to make it permanent or even add it to some profile file maybe if any, to use it always when become a user. This is very useful when working with console.