I am not sure for Debian based systems like Ubuntu, but nothing works for Fedora-based systems like CentOS to create additional admin users. You can find the same recommendation to add a sudoer on Virtualmin.com forums, however that method simply does not work. The only way of getting this done on CentOS is to follow this guy's finding: https://www.virtualmin.com/node/33013 However, I am not sure if it is the best way. For the sake of getting rid of all similar requests in the future could you, guys, finally create a documentation page for proper way of creating additional admin users?
Please create a documentation page for proper way of creating additional admin user