Originally Posted by palisetty_suman
Please don't show me wikipedia for that.
So you want us to act as your favorite encyclopedia?
The real UID of a process is the user id of the user that created the process. While the effective UID is that one used to evaluate privileges of the process to perform a particular action. During the process execution it is set by a setuid() system call. You can easily verify it using the command strace
against a process which requires root privileges to perform an action.
An example of such a command is passwd
which can be run by a normal user, but requires root privileges in order to modify the content of /etc/passwd every time you change your password.