as we all know that the new version of Kali Linux came up with no root user,it have just a kali user with password kali in order in minimize the privileges, and by default there is no super user anymore, but we can create the root user with its super privileges.
so, lets start
start up your Kali Linux with the kali/kali as username and password, after that open the terminal,
in terminal
sudo su
then press Enter,
the system will ask you about the password,
write down the kali password which is kali
so, i need you to notice now that your user has been switched to root,
so after getting the root user you should set a password to the user to be able to login with root user so, write
passwd
then press enter,
then write your root user password's twice to conform the password.
and now try to logoff and login with root, and enjoy using Kali Linux 2020 with your own superuser.
if you want to watch these steps in a video press here.
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good luck.