Ubuntu-- Enable Root Login

    If it is your first time to use Ubuntu, you cannot access Linux system as a root user. 

    That is because of the difference between Ubuntu installation without starting a root account and setting a root password and the regular Linux installation. 
    So, we can use "sudo".  Sudo is a tool for a common user to have the access permission as a super user. It is very easy. You can use "$ sudo passwd root" and then input a password you specify twice. After doing this, you can switch to a super user by using "$ su".
    There are two ways for you to make a root account.
    (1)use $ sudo passwd root;
        The system will let you input your password twice.

         Then,use the command $gksu /usr/sbin/gdmsteup. Several years ago, Linux operator uses $sudo /etc/X11/gdm/gdm.conf, but now gdm has changed a lot. If you cannot find gksu command, first you should install it.

        when done, use "$gedit /usr/etc/gdm/gdm.schemas" command, put the root in the below schema to above schema, then you can use root account to login.

    (2) on the system desk, open system>security>allow local system administrator login.
There we go!