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Ubuntu User Accounts

Introduction​

User account management is a fundamental aspect of any operating system, and Ubuntu is no exception. In multi-user environments like Ubuntu, understanding how user accounts work is essential for system security, resource sharing, and maintaining a well-organized computing environment.

In this guide, we'll explore everything you need to know about Ubuntu user accounts - from creating and managing users to understanding the underlying permission structure that keeps the system secure and organized.

Understanding Users and Groups in Ubuntu​

The Concept of Users​

In Ubuntu (and other Linux distributions), a user is an entity that can interact with the system and own files. Each user has:

  • A unique username
  • A unique numeric user ID (UID)
  • A home directory (typically /home/username)
  • A login shell
  • Password authentication
  • Membership in one or more groups

The Concept of Groups​

Groups in Ubuntu are collections of users that share similar access permissions. Key points about groups:

  • Each group has a unique name and group ID (GID)
  • Every user belongs to at least one group (their primary group)
  • Users can belong to multiple groups
  • Groups simplify permission management for multiple users

Let's visualize the relationship:

Types of User Accounts in Ubuntu​

Ubuntu has three main types of user accounts:

  1. Root User: The superuser (UID 0) with unlimited privileges
  2. System Users: Created by the system for running services
  3. Regular Users: Normal user accounts for people using the system

Viewing Existing Users and Groups​

Listing Users​

To see all users on your system:

bash
cat /etc/passwd

Output example:

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
...
ubuntu:x:1000:1000:Ubuntu:/home/ubuntu:/bin/bash

For a cleaner list of just usernames:

bash
cut -d: -f1 /etc/passwd

Output example:

root
daemon
bin
...
ubuntu

Listing Groups​

To see all groups:

bash
cat /etc/group

Output example:

root:x:0:
daemon:x:1:
bin:x:2:
...
ubuntu:x:1000:

To check which groups a specific user belongs to:

bash
groups username

Output example:

ubuntu : ubuntu adm cdrom sudo dip plugdev lpadmin sambashare

Creating User Accounts​

The adduser command provides an interactive way to create users:

bash
sudo adduser newusername

Output example:

Adding user `newusername' ...
Adding new group `newusername' (1001) ...
Adding new user `newusername' (1001) with group `newusername' ...
Creating home directory `/home/newusername' ...
Copying files from `/etc/skel' ...
New password: 
Retype new password: 
passwd: password updated successfully
Changing the user information for newusername
Enter the new value, or press ENTER for the default
        Full Name []: New User
        Room Number []: 
        Work Phone []: 
        Home Phone []: 
        Other []: 
Is the information correct? [Y/n] Y

Using useradd (More Control, Less Interactive)​

The useradd command gives more control but requires more specific parameters:

bash
sudo useradd -m -s /bin/bash -G sudo,adm newusername
sudo passwd newusername

In this command:

  • -m creates a home directory
  • -s /bin/bash sets the default shell
  • -G sudo,adm adds the user to the sudo and adm groups

Managing User Accounts​

Modifying User Properties​

To modify existing user properties, use the usermod command:

bash
# Add a user to a group
sudo usermod -aG groupname username

# Change a user's shell
sudo usermod -s /bin/zsh username

# Change a user's home directory
sudo usermod -d /newhome/username username

Changing Passwords​

Users can change their own passwords:

bash
passwd

Administrators can change any user's password:

bash
sudo passwd username

Deleting Users​

To remove a user account:

bash
# Keep the home directory
sudo deluser username

# Remove the home directory as well
sudo deluser --remove-home username

# Remove all user files across the system
sudo deluser --remove-all-files username

User Permissions and Ownership​

Understanding File Permissions​

In Ubuntu, every file and directory has three permission sets:

  • Owner permissions
  • Group permissions
  • Other (everyone else) permissions

Each set can have read (r), write (w), and execute (x) permissions.

To view permissions:

bash
ls -l filename

Output example:

-rw-rw-r-- 1 ubuntu ubuntu 1234 Apr 15 14:30 example.txt

Breaking this down:

  • -rw-rw-r--: Permissions string
    • First character - indicates a regular file
    • Next three characters rw- are owner permissions (read, write, no execute)
    • Next three characters rw- are group permissions (read, write, no execute)
    • Last three characters r-- are other permissions (read only)
  • ubuntu ubuntu: Owner and group names
  • 1234: File size in bytes
  • Apr 15 14:30: Last modification date
  • example.txt: Filename

Changing Permissions​

To modify file permissions:

bash
# Using symbolic notation
chmod u+x filename    # Add execute permission for owner
chmod g-w filename    # Remove write permission for group
chmod o=r filename    # Set other permissions to read-only

# Using numeric notation
chmod 755 filename    # rwxr-xr-x
chmod 644 filename    # rw-r--r--

Changing Ownership​

To change file ownership:

bash
# Change owner
sudo chown newowner filename

# Change group
sudo chgrp newgroup filename

# Change both owner and group
sudo chown newowner:newgroup filename

Sudo and Administrative Privileges​

Understanding Sudo​

The sudo command allows regular users to execute commands with administrative (root) privileges.

bash
sudo command

When you run a command with sudo, the system will:

  1. Ask for your password
  2. Check if you're in the sudo group
  3. Execute the command with elevated privileges if authorized

Adding a User to Sudo Group​

To give a user sudo privileges:

bash
sudo usermod -aG sudo username

Configuring Sudo Settings​

Sudo's behavior is controlled by the /etc/sudoers file. Always edit this file using:

bash
sudo visudo

Example of granting specific permissions:

# Allow user to run apt commands without password
username ALL=(ALL) NOPASSWD:/usr/bin/apt

Working with the Root User​

Root Account in Ubuntu​

By default, the root account in Ubuntu has no password set, which means direct login is disabled. Instead, Ubuntu encourages using sudo for administrative tasks.

If you need a root shell temporarily:

bash
sudo -i

This will give you a root shell after entering your password.

Enabling/Disabling the Root Account​

To enable direct root login (not recommended):

bash
sudo passwd root

To disable it again:

bash
sudo passwd -l root

Multi-User Best Practices​

When managing a system with multiple users, follow these best practices:

  1. Principle of Least Privilege: Give users only the permissions they need
  2. Regular Audits: Periodically review user accounts and remove unused ones
  3. Strong Passwords: Enforce strong password policies
  4. Group Organization: Create logical groups based on roles or departments
  5. Shared Directories: Use group permissions for collaboration spaces

Creating Shared Directories​

bash
# Create a shared directory
sudo mkdir /shared/projects

# Set appropriate ownership and permissions
sudo chown root:developers /shared/projects
sudo chmod 2775 /shared/projects

In this example:

  • The developers group owns the directory
  • The permissions 2775 include the SGID bit (2) which makes new files inherit the directory's group

User Management GUI​

Ubuntu Desktop provides a graphical interface for user management:

  1. Open "Settings"
  2. Select "Users"
  3. Click the "Unlock" button and enter your password
  4. Use the interface to add, remove, or modify user accounts

Summary​

Managing user accounts in Ubuntu is a foundational skill that enables secure multi-user environments. We've covered:

  • Understanding the concept of users and groups
  • Creating, modifying, and deleting user accounts
  • Managing permissions and ownership
  • Using sudo for administrative tasks
  • Best practices for multi-user systems

By mastering these concepts, you'll be able to manage Ubuntu systems efficiently while maintaining proper security.

Exercises​

  1. Create a new user account and add it to the sudo group.
  2. Create a shared directory for a group of users with appropriate permissions.
  3. Modify file permissions to allow a specific group to edit a file, but others only to read it.
  4. Find all files owned by a specific user using the find command.
  5. Create a new group and add several users to it.

Additional Resources​


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