Difference between sudo group and sudoers file?

I am creating a user in Ubuntu 14.04 using command adduser.

I want to give it sudo access. For doing this, I am consfused in between two ways.

First way is : If I add that user to sudo group using command usermod -aG sudo.

Second way is : If I edit the sudoers file using command visudo and add a line ALL=(ALL:ALL) ALL.

Please clear the confusion between these two.

Solution 1:

sudo group is not special by itself. It has sudo access because (if) there's a line like this in the sudoers file:

%sudo   ALL=(ALL:ALL) ALL

So it's the file that really matters anyway.

Solution 2:

The Ubuntu default /etc/sudoers configuration has two groups to allow sudo access. Members of these groups are allowed sudo access without requiring an edit to /etc/sudoers or the addition of a configuration file to /etc/sudoers.d.

# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

The preferred way to do local configuration addition is to add a file to /etc/sudoers.d with the required configuration. This allows the default configuration to be updated automatically. Use visudo to at least verify these changes