Use the following commands to create the new user dennis, grant him the same privileges as root and set him a password :

# useradd -ou 0 -g 0 dennis
# passwd dennis

Perhaps you already have some user dennis and you would like to give root permissions to a normal user.

# grep dennis /etc/passwd
dennis:x:1001:1001::/home/dennis:/bin/sh

Edit /etc/passwd file and grant root permissions to the user dennis by changing User and Group IDs to UID 0 and GID 0 :

# $ grep dennis /etc/passwd
dennis:x:0:0::/home/dennis:/bin/sh

You won't be able to delete second root user with another UID 0 using userdel command.

# userdel dennis
userdel: user dennis is currently used by process 1

To delete user dennis with UID 0, open /etc/passwd file and change dennis's UID.

For example, change the line :

dennis:x:0:0::/home/dennis:/bin/sh

to

dennis:x:1111:0::/home/dennis:/bin/sh

Now, you'll be able to delete user dennis with userdel command (as shown above)

 

Curious why you just don't run

/usr/sbin/visudo