Operating Systems · Chapter 13
OS Protection & Permissions Lab
Experiment with UNIX-style permissions and see how ownership, group membership, and requested operations affect access decisions.
Owner
Group
Others
Permission Summary
Symbolic mode–
Octal mode–
Access class–
Decision–
Change permissions or check an access request.
chmod 644 file.txt
Access Matrix
| Class | Read | Write | Execute | Octal value |
|---|---|---|---|---|
| Owner | – | – | – | – |
| Group | – | – | – | – |
| Others | – | – | – | – |
Concept Guide
Owner / Group / Others: UNIX permissions are evaluated using one of these three classes.
r = 4, w = 2, x = 1: add the enabled bits to obtain each octal digit.
Example: chmod 640 file.txt means owner can read/write, group can read, and others have no permissions.
Least privilege: give users and processes only the permissions they actually need.
This simulator models basic discretionary access control. Real systems may also apply ACLs, capabilities, SELinux/AppArmor policies, root privileges, namespaces, and other security layers.