コメントでいろいろ書いてますが、root権限付与のところは多分個人の場合はそのままvisudoにユーザ名を追記して、会社の場合はグループを変更したほうが良さそうです。
# HOW TO CREATE USER AND GROUP, GRANT ROOT PRIVILEGE
## PART1 CREATE USER
# assume user1,user2,user3 is already created
# and they are in wheel group, which can execute as root
# and here we're creating a new user named:new_user
# create new user
useradd new_user
# set password for it, in the prompt
passwd new_user
# you can now login as new_user
# but when you run sudo you may get this error
new_user is not in the sudoers file. This incident will be reported.
# so you need to set the privilege to new_user
## PART2 GRANT SUDO PRIVILEGE
## 1. BY CHANGE USER GROUP
$ visudo
############ in visudo ############
## Allows people in group wheel to run all commands
# %wheel ALL=(ALL) ALL
## Same thing without a password
%wheel ALL=(ALL) NOPASSWD: ALL
############ in visudo ############
# It means people in wheel group can run all commands, without password
# Below we're adding the new user called new_user to the wheel group.
# list users and user id, group id, home directory, login shell, etc.
$ cat /etc/passwd
...
wheel:x:10:root,user1,user2,user3
...
$ id -a [user name]
uid=503(user3) gid=503(init_group) 所属グループ=503(init_group),10(wheel)
$ usermod -g init_group -G init_group,wheel new_user
$ id -a new_user
uid=506(new_user) gid=503(init_group) 所属グループ=503(init_group),10(wheel)
## 2. BY ADD USER TO sudoers FILE.
$ visudo
############ in visudo ############
new_user ALL=(ALL) NOPASSWD: ALL
############ in visudo ############
## some handy commands
# show user list
$ cut -d: -f1 /etc/passwd
root
bin
daemon
adm
...
# TODO
# what is the difference between -g(initial_group) and -G(group)
# Reference
# (ENG) http://superuser.com/questions/120340/user-not-in-the-sudoers-file-this-incident-will-be-reported
# (JPN) http://kazmax.zpp.jp/linux_beginner/usermod.html
