What if I got 2 survey display at the survey homepage, but I only want to display one of the survey to specific user. For example: "A" user only can see the survey "A", so the survey "B" will be hidden to user "A".

Is that possible to do it?

It would probably be simplest to create separate stand-alone web pages listing the surveys.

real question is: how do you differentiate between the 2 users?

I dont know. So I ask is it possible to achieve that?

So you don't know what you are trying to do but you are asking us to solve it????

Sorry, but we need to better understand the circumstances of what you are trying to do, to give you an answer.

Otherwise the answer will be "It depends." and I guess this is not very helpful to you. Help us to help you.

In some way LS must need to know when to display survey A or survey B. How do people that should see A differ from those that should see B?

What we intent to achieve with LS is that to allow single registered user to be able to access survey that we allow this user to participate, however, administrator is the person who determine which survey the users could access.

In addition we do not want to let public access user to see the survey available until he/she has registered.

Can these be done from the LS configurations?

Limesurvey does not have a portal for "users" (survey respondents). Limesurvey has only a login section for survey administrators.