1. Introduction to Users and Groups
Multi-User System Concepts
Linux is designed as a multi-user operating system where:
- Multiple users can use the system simultaneously
- Each user has their own identity, permissions, and environment
- Users can belong to multiple groups
- Groups allow sharing resources among multiple users
- Security is enforced through user and group permissions
User Types:
System Users (UIDs 0-999)
- root (UID 0): Superuser with unlimited privileges
- System accounts (UIDs 1-999): Used by system services and daemons
- Examples:
www-data, mysql, sshd, nobody
Regular Users (UIDs 1000+)
- Human users with limited privileges
- Can only modify files in their home directory
- Need
sudo for administrative tasks
- Examples:
john, alice, student
Groups:
- Primary group: User’s main group (usually same as username)
- Secondary groups: Additional groups for shared access
- System groups: Used by system services
-
User-defined groups: Created for specific purposes
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