I have this question ,
My user is taking a leave for few days , and as an administrator I want to make logging impossible without affecting all file systems

What's the best choice:
1)Add * to his encrypted password
2)Delete the user from the /etc/password file
3)remove the users encrypted password
4)rename hi username to root
5)set his juserId to -1

Is this a domain login? Or a single machine? What operating system?

As an administrator your question doesn't make a whole lot of sense. Do you mean you want to disable the ability to login under that ID? If so we need to know what OS the network users. But if it's a Windows based network you can use Active Directory to disable the account for a period of time.