Linux User Management

What Is User Management?

Linux is a multi-user operating system, meaning multiple users can have separate accounts on the same machine. Each account has its own identity, permissions, and, usually, a home directory.

User management helps administrators control who can access the system and what each user is allowed to do.

In this lecture, we'll learn how to create users, view their details, switch between accounts, and delete users.

Creating a User

Linux provides the useradd command to create user accounts.

sudo useradd dev1

This creates a user named dev1. The command requires administrative privileges.

Important: On many Linux distributions, useradd does not create a home directory unless you specify the -m option. Defaults can vary depending on the system configuration.

Creating a User with a Home Directory

To create a user and a home directory together, use:

sudo useradd -m dev2

The -m option creates a home directory, typically /home/dev2.

A home directory provides a personal workspace where the user can store files and directories.

Setting a Password

Creating a user does not automatically set a password. Use passwd to assign one:

sudo passwd dev2

Enter and confirm the new password when prompted.

The same command can be used to change an existing user's password:

sudo passwd dev1

Viewing User Information

Linux provides several commands and system files for checking user details.

1. Check User and Group IDs

Use the id command:

id dev1

Example output:

uid=1001(dev1) gid=1001(dev1) groups=1001(dev1)

This output shows:

• uid: The user's unique numeric ID.
• gid: The ID of the user's primary group.
• groups: The groups the user belongs to.

The actual IDs and group memberships depend on the system.

2. View User Accounts

Linux stores basic account information in /etc/passwd.

cat /etc/passwd

Each line represents a user account, including system accounts used by services. Not every listed account represents a person who can log in interactively.

To find a specific account, use:

grep '^dev1:' /etc/passwd

Each entry contains seven colon-separated fields, including the username, user ID, primary group ID, home directory, and login shell.

Note: /etc/passwd does not normally store users' actual passwords. Password hashes are generally stored in /etc/shadow, which has restricted access.

Switching Between Users

The su command allows you to switch to another user account.

su - dev2

The - option starts a login shell, loading the target user's environment and normally placing you in their home directory.

Depending on the system configuration, switching may require the target user's password or authorization through another mechanism.

Verify the Current User

Use whoami to display the username associated with your current session:

whoami

Example output:

dev2

Check the Current Directory

Use pwd to display your current working directory:

pwd

After switching to dev2 with su - dev2, the output will typically be:

/home/dev2

To return to the previous shell, run:

exit

Understanding Home Directories

A home directory is a user's default personal workspace. For ordinary user accounts, it is commonly located under /home.

For example:

/home/
├── ubuntu/
├── dev1/
└── dev2/

You can list the directories under /home using:

ls /home

The output depends on which home directories have actually been created.

Remember that creating a user account does not always create a home directory. The -m option or the system's account configuration determines whether one is created.

Default Group Assignment

Linux uses groups to manage permissions for multiple users.

On many distributions, creating a user also creates a group with the same name and assigns that user to it. This is commonly called a user-private group setup.

For example:

id dev1

Possible output:

uid=1001(dev1) gid=1001(dev1) groups=1001(dev1)

Here, dev1 belongs to a group also named dev1. However, this behavior depends on the distribution and its configuration.

Users can also belong to additional groups, which is useful when multiple users need access to shared files or resources. Group management can be covered separately.

Deleting a User

Use userdel to remove a user account:

sudo userdel dev1

This removes the account, but does not necessarily delete the user's home directory or files.

To remove the account along with its home directory and mail spool, use:

sudo userdel -r dev1

Use the -r option carefully. Back up any files that need to be retained before deleting an account.

You can check whether the account still exists by running:

id dev1

If the account has been removed, the command reports that the user does not exist.

Quick Reference

Summary

• Linux supports multiple user accounts, each with its own identity and access permissions.
• Use useradd -m when you want to create a user with a home directory.
• Use passwd to set or change a user's password.
• Use id to inspect user IDs, primary group IDs, and group memberships.
• /etc/passwd stores basic account information, not the actual user passwords.
• Use su - username to switch users and load their login environment.
• userdel removes an account; userdel -r also removes its home directory and mail spool.

Best practice: Verify the account and back up any required data before deleting a user, especially on shared servers.

Written By: Muskan Garg