ITPEC FE Subject A April 2024 Question 33
ITPEC FE Subject A April 2024 — Question 33 of 60
Unix-style file permission bits (octal) — identifying which operations are allowed for a given octal value.
Three bits represent three permissions. Based on the trial results given in the problem,
the bit order is: execute (4) | write (2) | read (1)
| Octal | Binary | Execute | Write | Read |
|---|---|---|---|---|
| 0 | 000 | ✗ | ✗ | ✗ |
| 3 | 011 | ✗ | ✓ | ✓ |
| 4 | 100 | ✓ | ✗ | ✗ |
| 5 | 101 | ✓ | ✗ | ✓ |
| 6 | 110 | ✓ | ✓ | ✗ |
| 7 | 111 | ✓ | ✓ | ✓ |
Verify using the trial results:
- (1) 0 = 000 → no permissions ✓
- (2) 3 = 011 → read + write, no execute ✓
- (3) 7 = 111 → all permissions ✓
All three trial results confirm the bit order: execute=4, write=2, read=1
Why not others:
- (a) 2 = 010 → write only, not read+execution
- (b) 4 = 100 → execute only ✓ — correct
- (c) 5 = 101 → read + execute, not write only
- (d) 6 = 110 → execute + write, not read + write
Key rule: always derive bit weights from the trial results given — do not assume standard Unix rwx order.
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