Privilege factors

[Gopal Ghosh]

Dear All, could any one help me with Privilege available to *root /su/ sudo and
also the difference between the above three
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[gopalghosh@localhost ~]$ whoami

gopalghosh

[gopalghosh@localhost ~]$ login

login: root

Password:

Login incorrect {why it is saying Login incorrect as I am typing the correct
password}

[gopalghosh@localhost ~]$ login

login: root

Password:

Login incorrect

[gopalghosh@localhost ~]$ su

Password:        {when I logged as su it accepted the same password}

[root@localhost gopalghosh]# sudo ls

Desktop  Documents Download  Music  Pictures Public  Templates  Videos

[root@localhost gopalghosh]# exit exit

[gopalghosh@localhost ~]$ sudo nano

We trust you have received the usual lecture from the local System

Administrator. It usually boils down to these three things:

    #1) Respect the privacy of others.

    #2) Think before you type.

    #3) With great power comes great responsibility.

[sudo] password for gopalghosh:

gopalghosh is not in the sudoers file.  This incident will be reported. {how
to add my local login in sudoers file}
[gopalghosh@localhost ~]$
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Thanksregards