How to Create Groups in Linux – Introduction

Hello everyone! Today, we’re diving into an essential topic for any Linux user: how to create and manage groups. Understanding groups is crucial for managing permissions and access on a Linux system.

You can also watch this lesson’s video tutorial here.

Before I continue, if you intend to write the certification exam,
you can get our exam practice or preparation questions using this link, or contact us on info@tekneed.com.

So, let’s get started!

Types of Groups in Linux

In Linux, there are two types of groups: primary groups and secondary (or supplementary) groups.

Primary Groups

A primary group is created by default whenever a user is created. The primary group has the same name as the user. For example, if you create a user named john, a primary group called john is also created, and the user john is automatically added to this group.

Secondary Groups

Secondary groups are additional groups that users can be added to, which are not created by default. These groups are usually created manually by the user or the system administrator.

Understanding Group Attributes

When groups are created, their information is stored in the /etc/group file. Let’s explore this file:

cat /etc/group

You will see a list of groups with their attributes. Let’s create a new group to understand this better. To create a group, use the groupadd command followed by the name of the group:

groupadd sales

If you check the /etc/group file again, you’ll see the new sales group listed. Here’s a breakdown of the attributes:

• Group Name: sales
• Group Password: Represented by an x, stored in /etc/gshadow
• Group ID (GID): A unique identifier for the group, for example, 1010
• Group Members: Users who belong to this group

Adding Users to Groups

To add users to a group, we use the usermod command. For example, to add a user named lisa to the sales group:

usermod -aG sales lisa

Here, -aG appends the user to the group without removing them from other groups.

If you check the /etc/group file again, you will see lisa listed under the sales group. Similarly, you can add another user, tekneed, to the same group:

usermod -aG sales tekneed

Now, let’s verify:

cat /etc/group

You should see both lisa and tekneed in the sales group.

How to Create Groups in Linux – Red Hat Enterprise Linux

Now, let’s see how to create groups in linux, specifically in Red Hat.

Creating a Primary Group

When you create a user, a primary group is automatically created. For example:

useradd ola

Check the /etc/group file:

cat /etc/group

You’ll see the ola group created with a unique GID of 1012.

Creating a Secondary Group

To create a secondary group, use:

groupadd hr

Verify the creation:

cat /etc/group

You should see the hr group listed. It has a unique group ID of 1013.

Adding Users to a Secondary Group

The command used to add users to a group is usermod.
Take your time to look through the help manual of the usermod command.

Note: always use the append option when adding users to a group, so as not to overwrite the existing users in the group.

usermod -aG sales tekneed

Check the group file:

cat /etc/group

However, in RHEL 9; users do not get overwritten even when the append option is not used.

usermod -G sales tekneed2

Check the group file:

cat /etc/group

Deleting a Group

To delete a group, use the groupdel command:

groupdel hr

Verify the deletion:

cat /etc/group

Modifying a Group

To modify a group, use the groupmod command. For example, to change the name of a group:

groupmod -n newname oldname

Password Management

User passwords are stored in the /etc/shadow file, while group passwords (though rarely used) are stored in /etc/gshadow. For consistency when editing user or group information, use commands like vipw for users and vigr for groups to ensure both the password and shadow files are updated.

Editing User and Group Files

To edit user information safely:

sudo vipw

To edit group information:

sudo vigr

These commands ensure consistency between the /etc/passwd and /etc/shadow files, or the /etc/group and /etc/gshadow files.

How to Create Groups in Linux – Ubuntu

Adding a User

This has been comprehensively explained in our previous lesson.

To add a new user in Ubuntu, use the useradd command followed by the username. For instance, to create a user named ola, execute:

useradd ola

To set a password for ola, use:

passwd ola

You can verify the creation of the user by viewing the contents of the /etc/passwd file:

cat /etc/passwd | grep ola

Similarly, check the group file to confirm the creation of the user’s primary group:

cat /etc/group | grep ola

When a user is created, a primary group with the same name is also created. This primary group is crucial for managing user permissions and file ownership.

Creating Secondary Groups

In Linux, secondary groups are often used to manage additional permissions and access rights. On how to create groups in linux, use the groupadd command:

groupadd finance

Verify the creation of the group by checking the /etc/group file:

cat /etc/group | grep finance

Adding Users to Groups

Users can be added to secondary groups using the usermod command. This command allows for various modifications, including adding users to supplementary groups:

usermod -aG finance ola

Here, the -a option appends the user to the group without removing them from other groups, and the -G option specifies the supplementary group.

Verify the user’s group membership:

cat /etc/group | grep finance

To add multiple users to a group, repeat the command with different usernames:

usermod -aG finance tekneed
usermod -aG finance tekneed2

Note: If you do not use the -a option, it may remove the user from other supplementary groups.

Modifying and Deleting Groups

To modify group properties, use the groupmod command. For instance, to rename a group:

groupmod -n newgroupname oldgroupname

To delete a group, use the groupdel command:

groupdel finance

Verify the deletion:

cat /etc/group | grep finance

Editing Configuration Files Directly

While commands like usermod and groupmod are preferred for safety, direct editing of configuration files is possible for experienced users. The primary files to be aware of are:

• /etc/passwd: Stores user account information.
• /etc/shadow: Stores encrypted user passwords.
• /etc/group: Stores group information.
• /etc/gshadow: Stores secure group information.

To ensure consistency, always use the vipw command for editing user information and vigr for group information. These commands lock the files, preventing concurrent modifications.

For example, to safely edit the /etc/passwd file:

vipw

And for the /etc/group file:

vigr

After making changes, you may also need to edit the shadow files to ensure consistency:

vipw -s
vigr -s

Conclusion

Understanding how to create groups in Linux is fundamental for system administration. Groups help in organizing users and managing permissions efficiently. Understanding how to add, modify, and delete users and groups, as well as ensuring consistency in configuration files, is essential for maintaining a secure and well-organized system. Practice these commands, and you’ll become proficient in handling user groups on any Linux system.

For those preparing for the Red Hat Certified System Administrator (RHCSA) exam, mastering these concepts is crucial. Stay tuned for more tutorials, and don’t forget to subscribe, like, and share!

Happy learning!

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We believe that by the end of this tutorial, you now know how to create groups in linux; on both RHEL and Ubuntu systems.

TUTORIAL VIDEO ON HOW TO CREATE GROUPS IN LINUX

RHCSA 9 /EX200 EXAM PRACTICE QUESTION AND ANSWER