When you want to log on to a UNIX system, you are queried for a login name and a password. The login name is your unique name on the given UNIX system. The password is your secret key to the account, which, when selected carefully, is your guarantee that no one else (except root) can access your personal files.
Changing Your Login Name
For maximum security, some UNIX systems never allow your login name to change. Your name can be retired, but then it can never be used again. To get a new name, a totally new account must be created. Even on UNIX systems that allow the administrator to change the login name, choose the name carefully so that you won’t have to ask for a change later.
You can change your password yourself, but your ...