5.2 Creating Users and Groups (Weight: 2)

📘Linux Essentials (LPI 010-160)

Managing users and groups is an important part of Linux system administration. Linux is a multi-user operating system, meaning multiple users can access the system at the same time. Each user has their own account, files, and permissions.

System administrators must manage these users and groups to control who can log in, what they can access, and what actions they are allowed to perform.

This section explains the commands, files, and concepts used to manage users and groups in Linux.

1. What is User and Group Management?

User and group management refers to the tasks involved in:

Creating user accounts
Modifying user accounts
Deleting user accounts
Creating and managing groups
Assigning users to groups
Controlling user access and permissions

These tasks are usually performed by the root user or by users with administrative privileges.

In an IT environment, administrators manage users to:

Provide login access to employees
Organize users into teams or departments
Control access to system resources
Maintain system security

2. User Accounts in Linux

A user account allows a person or service to access the Linux system.

Each user account contains several pieces of information such as:

Username
User ID (UID)
Primary group
Home directory
Default shell
Password

This information is stored in system files such as:

/etc/passwd
/etc/shadow
/etc/group

3. Important Files Used for User Management

3.1 /etc/passwd

The /etc/passwd file stores basic information about user accounts.

Each line represents one user account.

Example:

john:x:1001:1001:John Doe:/home/john:/bin/bash

Fields in /etc/passwd:

Field	Description
Username	Login name of the user
Password placeholder	Usually `x`, meaning password stored in `/etc/shadow`
UID	User ID number
GID	Primary Group ID
Comment	Description or user information
Home directory	User’s home directory
Shell	Default login shell

3.2 /etc/shadow

The /etc/shadow file stores encrypted user passwords and password policies.

Example:

john:$6$abc...:19000:0:99999:7:::

This file is readable only by the root user for security reasons.

Information stored includes:

Encrypted password
Password aging rules
Account expiration information

3.3 /etc/group

The /etc/group file stores group information.

Example:

developers:x:1002:john,mary

Fields include:

Field	Description
Group name	Name of the group
Password	Usually unused
GID	Group ID
Members	Users in the group

4. Creating Users

In Linux, new users are created using the useradd command.

Basic syntax:

useradd username

Example:

sudo useradd alice

This creates a new user account.

However, it usually does not create a home directory unless specified.

Creating a User with Home Directory

sudo useradd -m alice

Option explanation:

Option	Meaning
`-m`	Create home directory

Home directory created:

/home/alice

Setting a User Password

After creating a user, a password must be set.

Command:

sudo passwd alice

The system will ask for the new password.

5. Useful useradd Options

Administrators often use additional options when creating users.

Option	Purpose
`-m`	Create home directory
`-d`	Specify custom home directory
`-s`	Set login shell
`-c`	Add user description
`-u`	Specify UID
`-g`	Set primary group
`-G`	Assign additional groups

Example:

sudo useradd -m -s /bin/bash -c "Web Administrator" -G developers alice

This creates a user with:

Home directory
Bash shell
Description
Membership in the developers group

6. Modifying Users

Existing users can be modified using the usermod command.

Syntax:

usermod [options] username

Changing a User’s Home Directory

sudo usermod -d /home/newdir alice

Changing Login Shell

sudo usermod -s /bin/zsh alice

Adding a User to a Group

sudo usermod -aG developers alice

Option explanation:

Option	Meaning
`-a`	Append (do not remove existing groups)
`-G`	Supplementary groups

This adds the user to an additional group.

7. Deleting Users

Users can be removed using the userdel command.

Syntax:

userdel username

Example:

sudo userdel alice

This removes the user account but keeps the home directory.

Removing User and Home Directory

sudo userdel -r alice

Option:

Option	Meaning
`-r`	Remove home directory and mail spool

8. Groups in Linux

A group is a collection of users.

Groups help administrators manage permissions more easily.

Instead of giving access to each user individually, access can be given to a group.

For example, a development team can be placed in a developers group so that all members share access to development resources.

Each group has:

Group name
Group ID (GID)
Members

9. Creating Groups

Groups are created using the groupadd command.

Syntax:

groupadd groupname

Example:

sudo groupadd developers

10. Modifying Groups

Groups can be modified using the groupmod command.

Example: change group name

sudo groupmod -n devteam developers

Option:

Option	Meaning
`-n`	New group name

11. Deleting Groups

Groups can be removed using the groupdel command.

Example:

sudo groupdel developers

This deletes the group from the system.

12. Primary and Secondary Groups

Each user belongs to at least one group.

There are two types:

Primary Group

The primary group is assigned when the user account is created.

It is stored in /etc/passwd.

Example:

alice:x:1002:1002

Here 1002 is the primary group ID.

Secondary (Supplementary) Groups

Users can belong to additional groups.

These are stored in /etc/group.

Example:

developers:x:1003:alice

This allows the user to access additional resources.

13. Viewing User and Group Information

Administrators often need to check user and group details.

id Command

Shows user ID and group membership.

Example:

id alice

Output example:

uid=1002(alice) gid=1002(alice) groups=1002(alice),1003(developers)

groups Command

Shows which groups a user belongs to.

groups alice

getent Command

Displays user or group database entries.

Example:

getent passwd alice

14. Managing Password Policies

Passwords are managed using the passwd command.

Example:

passwd alice

This allows administrators to:

Set passwords
Lock accounts
Unlock accounts
Force password changes

Locking a User Account

sudo passwd -l alice

Unlocking a User Account

sudo passwd -u alice

15. Example of User Management in an IT Environment

A system administrator may perform tasks such as:

Creating user accounts for new employees
Assigning users to department groups
Removing accounts when employees leave
Locking accounts during security incidents
Managing access to shared directories

Using groups allows administrators to manage permissions efficiently for teams such as:

developers
administrators
database administrators
system operators

16. Security Best Practices

For secure user management:

Only administrators should create or modify users
Use strong passwords
Remove unused accounts
Use groups instead of individual permissions
Lock accounts when necessary
Regularly review user and group memberships

These practices help maintain a secure Linux environment.

17. Key Commands to Remember for the Exam

Command	Purpose
`useradd`	Create user
`usermod`	Modify user
`userdel`	Delete user
`groupadd`	Create group
`groupmod`	Modify group
`groupdel`	Delete group
`passwd`	Manage passwords
`id`	Display user information
`groups`	Show group membership
`getent`	Query system databases

✅ Exam Tip:
For the Linux Essentials exam, you should understand:

How Linux stores user and group information
Commands used to create, modify, and delete users
Commands used to manage groups
Difference between primary and secondary groups
Basic commands to check user information

These topics form the core of Managing Users and Groups in Linux.