useradd command /usermod command /groupadd command (user management) commands in linux

Managing users and groups is an essential skill for any Linux system administrator. This guide provides a clear overview of the basic commands and files involved in creating, modifying, and deleting users and groups on a Linux system.

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Creating Users

To add a new user to the system, use the following command:

useradd username

Example:

useradd sharecodepoint

This command creates a new user called sharecodepoint.

Note: Only the root user can create new users. To switch to root, type:

su -

Enter the root password (it won’t be visible as you type — don’t worry!).

User Account Information Files

Linux stores user-related information in these key files:

• cat /etc/passwd – Contains one line for each user account.
• cat /etc/group – Defines the groups on the system.

Set Password for User

To set a password for a user:

passwd username

Example:

passwd sharecodepoint

You’ll be prompted to enter the new password.

Delete a User

To remove a user from the system:

userdel username

Example:

userdel sharecodepoint

To view the list of existing users:

cat /etc/passwd

Understanding the /etc/passwd File

Each entry in the /etc/passwd file has the format:

user:password:UID:GID:comment:home:shell

• Username: Login name (1–32 characters)
• Password: Encrypted, stored in /etc/shadow
• UID (User ID): Unique numeric ID for the user (0 for root, 1-99 for system, 100-999 for other system accounts)
• GID (Group ID): User’s primary group ID from /etc/group
• Comment/User Info: Optional; full name or additional info
• Home Directory: Path to user’s home directory
• Shell: Default shell (e.g., /bin/bash)

Creating a Group

To create a new group:

groupadd groupname

Example:

groupadd cappractice

To view existing groups:

cat /etc/group

Adding Users to Groups

You can use either useradd or usermod to add a user to a group.

There are two types of groups:

1. Primary Group: Default group assigned to a user.
2. Secondary/Supplementary Group: Additional groups a user belongs to.

Primary Group

The primary group is defined by the 4th field in /etc/passwd. Files and directories created by the user will belong to this group.

Secondary Groups

Users can be part of additional groups. These are managed via /etc/group.

To add a user to a secondary group:

useradd -G groupname username

Example:

useradd -G cappractice sharecodepoint

To add a user to multiple groups:

useradd -G admins,ftp,www,developers jerry

Use uppercase -G to specify secondary groups.

Add User to Primary Group

To assign a user to a primary group:

useradd -g groupname username

Example:

useradd -g developers tony
id tony

Use lowercase -g to specify the initial login (primary) group.

Change a User’s Primary Group

To change a user’s primary group:

usermod -g groupname username

Add an Existing User to a Group

To add an existing user to a secondary group:

usermod -a -G groupname username

Example:

usermod -a -G ftp tony

To change the primary group for the user:

usermod -g www tony

Use -a only with -G to avoid overwriting existing group memberships.

Delete a Group

To delete a group:

groupdel groupname

Example:

groupdel cappractice

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This guide gives you a solid foundation in managing Linux users and groups. Whether you're setting up new accounts or configuring group permissions, mastering these commands will make your system management smoother and more secure.