User Management

Understanding Linux Users

Types of Users

Root user (UID 0)
System users (UID 1-999)
Regular users (UID 1000+)

User Information

Username
User ID (UID)
Group ID (GID)
Home directory
Default shell

User Management Commands

Creating Users

useradd -m username    # Create user with home directory
useradd -s /bin/bash -m username  # Specify shell
adduser username       # Interactive user creation

Modifying Users

usermod -s /bin/zsh username  # Change shell
usermod -L username           # Lock account
usermod -U username           # Unlock account
usermod -aG group username    # Add to supplementary group

Deleting Users

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

Group Management

Creating Groups

groupadd groupname     # Create new group
groupadd -g 1001 groupname  # Specify GID

Modifying Groups

groupmod -n newname oldname  # Rename group
groupmod -g 1002 groupname   # Change GID

Managing Group Membership

usermod -aG sudo username   # Add to sudo group
gpasswd -a user group       # Add user to group
gpasswd -d user group       # Remove from group

Access Control

Understanding sudo

Controlled privilege escalation
Configuration in /etc/sudoers
Command-specific permissions

Configuring sudo Access

visudo                  # Edit sudoers file safely
# Example configurations:
user ALL=(ALL) ALL     # Full sudo access
user ALL=(ALL) NOPASSWD: ALL  # No password required

Best Practices

Use least privilege principle
Regular audit of sudo access
Remove unnecessary privileges
Document access changes

Password Management

Setting Passwords

passwd username        # Set user password
chage -d 0 username    # Force password change
chage -M 90 username   # Set maximum password age

Password Policies

Minimum length requirements
Complexity rules
Password aging
History restrictions

Hands-on Practice

Exercise 1: User Creation

Create a new user: sudo useradd -m testuser
Set password: sudo passwd testuser
Add to groups: sudo usermod -aG sudo testuser
Verify setup: id testuser

Exercise 2: Group Management

Create group: sudo groupadd developers
Add users: sudo gpasswd -a testuser developers
Verify membership: groups testuser

Security Considerations

Account Security

Regular password changes
Account lockout policies
Failed login monitoring
Session timeout settings

Audit and Monitoring

last                   # View login history
w                      # Show logged-in users
who                    # List current users
auth.log              # Authentication log file

Additional Resources

Next Steps

Implement user policies
Configure PAM modules
Set up LDAP authentication
Learn about access control lists