console 1:
root@localhost:/home/userx# /sbin/usermod -aG sudo userx

console 2:
userx@localhost:~$ groups userx
userx : userx cdrom floppy sudo audio dip video plugdev netdev bluetooth scanner
userx@localhost:~$ sudo whoami
[sudo] password for userx:
userx is not in the sudoers file.  This incident will be reported.