I don’t want people to use my machine without my presence since I have a lot of cookies and files stored on this machine. So I hope each time the system starts it shows login window and asks for account/pwd. How can I do it?
Thank you in advance.
Which desktop?
It can be done in Yast but it it easier to do it from say KDE’s Personal Settings -System- Login Manager screen. I think there is an equivalent in gnome
You probably mean “I don’t want people to use my userid” instead of you “machine”. Every user should have his/her own userid (username/passwd) and is responsable for her/his own cookies, files, etc.
You should not have switched on “automatic login” (see @gogalthorp’a advice how to do this). And you should not let anybody use your userid with or without your presence. When you want to allow anybody to use your system, give her/him a userid.
Autologin is the default, at least it was already ticked for me when I installed 11.2 (as well as ‘use my password for root password’)
Both are pretty bad defaults really.
Whats the point of having a password if you never have to use it because you’re logged in regardless of who turns the computer on (the guy who steals your laptop is gonna love those topless photos of your missus in the handily named ‘Photos’ directory)?
And who wants the root password to be the same as a particular users password?
Agreed, but they are only defaults, you can change that already during install and there are several threads here that advise this.
Sure you can change them, at install or later on through (I presume) Yast. The question is though: who does?
The problem is, most people just accept defaults. Justifiably so as well - otherwise, why have defaults at all if they are not a ‘reasonable’* configuration for a majority of users to have?
You said above that ‘You should not have switched on “automatic login”’, but he didn’t - openSuse turned it on for him. I’m not having a dig or anything, I just think that if the software does something that turns out to be wrong**, its the software’s fault.
*For some definition of reasonable: stable & secure would be mine 
**Wrong as in either broken, or causes more problems than it fixes
I started my answer with “Agreed” and that is realy the main part of my answer. IMHO the defaults should be different!
But the “other people” (those who make these defaults) seam to to have their argument. These are something like “The default install should run without login and without a proper root protection, because that is done in Windows and when it is different we shy Windiows users away from Linux”.
They could be right, I am not the one who knows much about the broken psychology of those who are exposed to a Wiindows OS during some time.
We’ll agree to agree then!
I suppose it depends which question you want to ask:
Why have security if your very next move is to completely bypass that security
or
How do we make it work like <other os> so we don’t confuse people who are used to <other os>
Market domination = defacto standard I guess. In Win98 you could just click cancel on the login prompt to get access, perhaps its the way to go?
Reading all that above, I think I’m getting old; These kids and their ‘music television’, bah!
I agree again (I am old >:( ).