Linux Basics - Adding users and groups

This short introductory post will walk you through adding a user, creating a group, adding the user to the group and sudoers, and setting up a shared folder with proper permissions on Ubuntu Linux.

The end goal is to end up with two user who can play the role of Alice and Bob as is typically the case for lot of cryptographic operations.

[! IMPORTANT] This blog assumes you already are logged into Ubuntu Linux with one user and all we are doing here is creating a second one. Alternately you can reuse the same script and create two distinct users if you wish to do so.

1. Add a User Named bart

Firstly, let’s create a new user named bart :

sudo adduser bart

You will be prompted to set a password and provide some additional information (which you can skip by pressing Enter).

Adding user `bart' ...
Adding new group `bart' (1005) ...
Adding new user `bart' (1004) with group `bart' ...
The home directory `/home/bart' already exists.  Not copying from `/etc/skel'.
New password: 
Retype new password: 
passwd: password updated successfully
Changing the user information for bart
Enter the new value, or press ENTER for the default
	Full Name []: Bart Simpson
	Room Number []: 
	Work Phone []: 
	Home Phone []: 
	Other []: 
Is the information correct? [Y/n] Y

The adduser command will create a home directory for Bart at /home/bart and configure appropriate default settings.

2. Create a Group Called cryptogrp

Next, we’ll create a new group named cryptogrp :

sudo groupadd cryptogrp

This command will create a group with the name cryptogrp on your system.

3. Add the user bart to Both cryptogrp and sudo

Now, let’s add user bart to the cryptogrp group and also to the sudo group, which grants administrative privileges:

sudo usermod -aG cryptogrp bart
sudo usermod -aG sudo bart

The usermod command with the -aG option appends user bart to the specified groups.

Use this command to check that group has been created

grep cryptogrp /etc/group

cryptogrp:x:1006:mikey,bart

4. Create a Shared Folder Location for Files

We’ll create a shared directory where members of cryptogrp can store files:

sudo mkdir /srv/shared

5. Give cryptogrp Access to the Shared Folder

Finally, we need to set the permissions so that members of cryptogrp can read, write, and execute files in the shared directory:

sudo chown :cryptogrp srv/shared
sudo chmod 770 srv/shared

• chown :cryptogrp /shared changes the group ownership of the /shared directory to cryptogrp.
• chmod 770 /shared sets the permissions so that the owner and the group have read, write, and execute permissions, while others have no access.