How to grant user process some privilege capabilities

[kaima]

I am writing a program which first runs as root but later switches itself to a normal user. And while running as normal user, it desires to call settimeofday(), which only allows root to call.

Is there any solution for this?

I guess maybe there is a thing like this:

main()
{
//(1) - I am still root here
grant_capability_of_set_system_datetime();
//(2) - I am becoming a normal user now
setuid(400);
setgid(400);
//(3) - Set time here
settimeofday();
}

I guess getcap() and setcap() might do (1), but I couldn't find any usage example.

[kaima]

I've just found this:

Using Capabilities

I'll tell if I can make it