There's no system call which changes UID and EUID from non-root to root. The way all the tools that do that do it is by having a setuid bit set which causes EUID to change when they are executed. If possible, however, you want to avoid having your application setuided since it is a security risk and it's much better to relay on existing commands such as the ones already listed in this thread (you might want to use witch to see which is available and then use that one).

Unfortunately, I can ask user about changing file system permissions. How you can imagine an installer, that ask you to change your system before it can start?

As a matter of fact, installers should require that you be an administrator, or that you "run-as" the installer under an administrator ID.

If you are a non-privileged user, the installer should either offer to do an install ("for you alone") that you can carry out, or it should politely inform you that you can't do it.

Totally agree your point of view, I also think this solution will be greate, but our marketing came from other galaxy and they require install to ask user about this.

Then you ignored the clue I left for you:
but then again that's understandable as the problems you face are not caused by technology (alone):

Not at all, and even the exact opposite. Installer should allow installation without root privileges to user's home directory.

that's what sundialsvcs actually said

Have you tried using the system call "setuid" ? (it might not allow you to become root, but see if it helps you in any way )

Sure, but as you wrote, this system call do not allow to get root permissions.

Yes, it really does come down to one of three things:

1. Install the application local to yourself.
2. Install the application globally, but only if you have root privileges.
3. Run the installer as root.

"The marketing department" should not be the one to set technical strictures. If there is not an easy, universal way to meet that request, then the bottom line is simply that the request cannot be met. There are plenty of systems out there which require that you be logged-in as certain users to do certain things. Precedents abound.

I've defeated this argument simply by pointing out that the developer-cost for the project is running about $14,000 (USD) per day, and that the time-equals-money is better spent making the product as easy to use "in the technically right way" than to continue to entertain the preferences of someone who really doesn't know the foot on which he stands.

this is definately the M$ windoze way of thinking of things, as up until vi$ta, most people were running by default as administrator, so things would just install (at least on home units), even on WINDOWS networks within corporations, an administrator was necessary to install stuff (for the most part), so this is a ridiculous requirement whether you are talking windows OR Linux.

think of it from another standpoint
if this were possible, how many Linux boxes would be owned by hackers/botnets?

Right, but regardless I don't consider politely informing you that you can't do it as a valid option.

ssue is solved by providing a root passphrase directly to su utility. It can be easily reached by using fd_set or pipes and system call forkpty that returns a ready to login shell.

Please check my post that describe this question and shows a solution: http://www.andreypudov.com/2013/02/u...-in-linux.html