If you heard about users and groups in linux… and you keep forgetting the essentials command, here is a cheatsheet.

User

List all existing users in ubuntu (prefered)
getent passwd

Another alternative method :
less /etc/passwd

Group

List all existing groups (prefered)
getent group

Another alternative method :
less /etc/group

Create a new group

Let’s create a docker group:
sudo groupadd docker
And add us ($USER) to this new group:
` sudo usermod -aG docker $USER`

Tip : Logout & login again for the previous lines to be taken into account.

Note

You can always filter the output usgin grep. So for instance if you are looking every group for a user type
getent group | grep username

Modifiying sudo rights

If you want to deal with sudo (admin priviledges) then you will have to modify a file located here /etc/sudoers which looks like this :

# User privilege specification

root ALL=(ALL:ALL) ALL

# Allow members of group sudo to execute any command

%sudo ALL=(ALL:ALL) ALL

# See sudoers(5) for more information on "#include" directives:

#includedir /etc/sudoers.d

Note: sudo rules can also be defined in files under the /etc/sudoers.d/ directory in case “#includedir /etc/sudoers.d” is not commented out.

Removing password prompt for users in the sudo group

You will need to modifiy the file like this :

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

Removing password prompt for a specific app

Let’s say you want sudo users not to have to type sudo every time they run any docker command. Then you will need to add this line in our file:

%sudo ALL=(ALL:ALL) NOPASSWD: /sbin/docker

Note for more security, you could simply create a docker group and grant this privilege to user member of the docker group only :

docker ALL=(ALL:ALL) NOPASSWD: /sbin/docker

Reference

Show users and group : stackoverflow
Modifiy sudo : askubuntu