LFCS: Users and Groups (10%)

This document covers user and group management, environment profiles, ACLs, resource limits, and LDAP integration.

Goals Coverage

Users and Groups 10%

1. Create and manage local user and group accounts
2. Manage personal and system-wide environment profiles
3. Configure user resource limits
4. Configure and manage ACLs
5. Configure the system to use LDAP user and group accounts

1. Create and Manage Local User Accounts

Learn

• Add, modify, and delete local users.
• Manage home directories and shells.

Commands

# Add user
sudo useradd -m -s /bin/bash username
sudo passwd username

# Modify user
sudo usermod -aG sudo username   # Add to group
sudo usermod -d /new/home username  # Change home directory

# Delete user
sudo userdel -r username   # Delete user and home directory

Exercises

1. Create a user with home directory and bash shell.
2. Add the user to the sudo group.
3. Remove a test user.

2. Create and Manage Groups

Learn

• Create, modify, and delete groups.
• Assign users to groups.

Commands

# Create group
sudo groupadd developers

# Modify group
sudo gpasswd -a username developers

# Delete group
sudo groupdel developers

# List groups
groups username

Exercises

1. Create a group admins and add a user.
2. Verify the user is part of the group.
3. Delete the group.

3. Manage Environment Profiles

Learn

• System-wide vs user-specific profiles.
• Configure PATH, variables, and shell startup files.

Commands

# Edit system-wide profile
sudo nano /etc/profile
sudo nano /etc/bash.bashrc

# Edit user profile
nano ~/.bashrc
source ~/.bashrc  # Reload changes

Exercises

1. Add a directory to PATH in .bashrc and reload.
2. Set a custom environment variable system-wide.

4. Configure User Resource Limits

Learn

• Use ulimit and /etc/security/limits.conf for limits on processes, open files, and memory.

Commands

# Temporary limit
ulimit -n 4096

# Persistent limit
sudo nano /etc/security/limits.conf
# user soft nofile 4096
# user hard nofile 8192

Exercises

1. Increase the maximum number of open files for a user.
2. Verify limits with ulimit -a.

5. Configure and Manage ACLs (Access Control Lists)

Learn

• Set fine-grained permissions beyond standard Unix mode bits.
• Commands: getfacl and setfacl.

Commands

# Check ACL
getfacl /path/to/file

# Set ACL for user
setfacl -m u:username:rwx /path/to/file

# Remove ACL
setfacl -x u:username /path/to/file

Exercises

1. Give read/write access to a specific file for a user without changing group ownership.
2. Remove the ACL and verify permissions.

6. Configure the System to Use LDAP for Users and Groups

Learn

• Integrate Linux system with LDAP server for centralized authentication.
• Configure NSS and PAM.

Commands

# Install LDAP client
sudo apt install libnss-ldap libpam-ldap ldap-utils

# Configure /etc/nsswitch.conf
sudo nano /etc/nsswitch.conf
# passwd: files ldap
group: files ldap
shadow: files ldap

# Test LDAP user
getent passwd ldapuser
id ldapuser

Exercises

1. Connect a Linux system to an LDAP server.
2. Verify that LDAP users can login.

Exam Tips

• Practice creating users and groups both locally and via LDAP.
• Understand persistent vs temporary environment variable settings.
• Familiarize with ACL commands for fine-grained permission control.