Adding users, groups and superusers in Linux

It is easy, and very important topic: the creation of different users who have accesses with different privileges. Even though the root user is the superuser who has all the privileges within the system, it is a risk to start client services with root, since the user could start or kill services that could compromise the security of the system.

However, it is necessary to use the root user to create the users, at least the second user within the system. Another option is to create the user from some other superuser (via su) or by typing sudo before each command. When creating a user, it is necessary to define a name and password by means of the following command:

useradd -m -G sales john

In this example we create the user juan, add it to the sales group (with the -G option) and create its directory (which will be /home/john)

To add a password, the following command is sufficient, where we add the password and its confirmation.

passwd john

To create a user and add it to a group, it is important to have previously created the group, if it has not been done, it is sufficient to execute the following command with the name of the group:

groupadd sales

How to rename an existing user in Linux

To rename a user in Linux, we can use the usermod command,

usermod -l new_user-name old_user-name 

You can refer to the detailed tutorial HERE to rename user or a group in Linux.

Also Read:- Introduction to Bash Scripting Tutorial

How to make my user a superuser

To make a superuser, it must belong to the root group, which must be assigned from the creation of the user, or by adding it like this:

usermod -aG sudo john

Where juan will be part of the sudo group (For Ubuntu distributions). If using a CentOS or derived distribution, the wheel group is used:

usermod -aG wheel username

And after adding the user as superuser, we test it by accessing superuser mode like so:

su - john

Or by accessing any command with superuser when using sudo:

sudo command

And entering the password of the superuser user.

How to see the existing users and groups on my server?

As superuser you can see the users with the users command and the groups with the groups command. The group information is stored in the /etc/group file and the users information, as well as their home directories are located in /etc/passwd, however if the passwords are encrypted, they are stored in the file /etc/shadow.