User Management

Create

useradd <username>

Delete

userdel -r <username>

Change Password

passwd <username>

Disable Account

passwd -l <username>

Assign root permissions

For Debian

vi /etc/sudoers

<username> ALL=(ALL) NOPASSWD: ALL

Impersonate root

For CentOS/Linux
Give an account root permissions. (Different from above)
This will make the user seen as root even though logged in as a different account.

vi /etc/passwd

Find the user in question and modify assigned number, typically 500:500 to be 0:0 example
from

timmy:x:500:500::/home/timmy:/bin/bash

to

timmy:x:0:0::/home/timmy:/bin/bash