File System · 4.4
File Protection
A file system must protect data from accidental or unauthorised access. Permissions and access-control rules decide what each user or process may do.
Permission checker
Toggle permissions in the table, then test an operation. The familiar UNIX-style order is owner, group and others.
| Subject | read | write | execute | Bits |
|---|---|---|---|---|
| owner | rwe | |||
| group | r-- | |||
| others | r-- |
Current mode
rwe r-- r--
Equivalent to a compact permission display.
Test access
Access denied: group may not write this file.
Protection concepts
Authentication — Verifies who the user or process is, such as with a password or identity token.
Authorisation — Checks what an authenticated subject is allowed to do with a resource.
Access control — A policy and enforcement mechanism that protects files, folders and devices.
Real-world analogy: A locked workshop
Authentication checks your identity at the door. Authorisation checks your assigned badge, and the access-control mechanism keeps the tools and rooms restricted according to that badge.
Quick quiz
1. What does the write permission allow?
2. Which check answers “who are you?”