The operating system controls file access through a system of permissions that dictate who can perform specific actions on a file.
Access Control Lists (ACLs)
The operating system maintains an Access Control List (ACL) for each file. This list specifies the users or groups who have permission to access the file and what actions they can perform.
- Read: Allows users to view the contents of the file.
- Write: Permits users to modify the file's contents.
- Execute: Enables users to run the file if it's an executable program.
- Delete: Grants users the ability to remove the file.
User and Group Permissions
Permissions are assigned to individual users and groups.
- Users: Each user account has its own set of permissions.
- Groups: Multiple users can be grouped together, and permissions can be applied to the entire group.
Example
Let's say you have a document named "report.docx." The operating system might grant:
- Read and Write access to the document's owner.
- Read-only access to a group of colleagues.
- No access to other users on the system.
Benefits of File Access Control
- Data Security: Prevents unauthorized access to sensitive information.
- Data Integrity: Ensures that only authorized users can modify files.
- System Stability: Limits the potential for accidental file deletion or modification.
Conclusion
By managing file permissions through ACLs, the operating system effectively controls who can access and modify files, ensuring data security, integrity, and system stability.
