I'm running Ubuntu Server 11.04. It came time to add User to the sudoers file: so I decided to simple add User to the admin group:
usermod -a -G admin user
Then I used visudo to check if admin users had been set to receive sudo privileges. I uncommented the line
admin ALL=(ALL) ALL. And viola!
Nothing happened. I've even tried to add user directly into the sudoers file as
user ALL=(ALL:ALL) ALL, but that failed too.
root ALL=(ALL:ALL) ALL
admin ALL=(ALL) ALL
%sudo ALL=(ALL:ALL) ALL