LAB-PERM-02 - UGO and the chmod Command

Part A: The Field Guide

Symbolic chmod is useful when you want to change one part of the permission state without replacing everything.

The structure is:

chmod [who][operator][what] file

Examples:

• u+x add execute for the owner
• g-w remove write from the group
• o= remove all permissions for others

The main pieces

• u owner
• g group
• o other
• a all

Operators:

• + add
• - remove
• = replace that target’s permissions exactly

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Part B: The Drill Deck

Terminal required: create a sandbox and keep all changes there.

G

Guided Step by step - type exactly this and compare the result

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Exercise G1: Build the sandbox

Create a practice area

mkdir -p ~/perm_lab cd ~/perm_lab touch test.txt ls -l test.txt

Copy

Exercise G2: Add one permission

1. Run chmod u+x test.txt
2. Run ls -l test.txt
3. Explain exactly what changed and who it affected

Exercise G3: Remove one permission

1. Run chmod g-w test.txt
2. Run ls -l test.txt
3. Explain exactly what changed and who it affected

Exercise G4: Replace one target

1. Run chmod o= test.txt
2. Run ls -l test.txt
3. Explain why o= is stronger than o-w

S

Solo Task described, hints available - figure it out

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Exercise S1: Predict before running

Starting from -rw-r--r--, predict the result of each command:

1. chmod u+x file.txt
2. chmod g-w file.txt
3. chmod o= file.txt

Then test your predictions in the sandbox.

Exercise S2: One-line reasoning

Write one sentence for each operator:

• what + is for
• what - is for
• what = is for

M

Mission Real scenario - no hints, combine multiple skills

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Mission M1: Secure one private file

In your sandbox:

1. create a file called private.txt
2. use symbolic chmod to give the owner read and write
3. remove all permissions from group and other
4. verify the final string with ls -l

If you can do that without defaulting to 777 or guessing, the symbolic model is working.