Linux Permissions & Chmod Security
Linux protects files using a 3-tier permission model (User, Group, Others) with Read (4), Write (2), and Execute (1) bits. Understand octal modes like 755 and 644.
Lesson Objectives
4 Steps1Step 1: Inspect Current File Permissions
Run `ls -l /var/log/auth.log` and note the permission string (e.g., `-rw-r--r--`).
2Step 2: Grant Executable Permissions to Script
Run `chmod 755 /home/user/projects/demo.sh` to give owner full access and others read/execute.
3Step 3: Restrict Sensitive Private Keys
Run `chmod 600 welcome.txt` to restrict read/write access strictly to the owner.
4Step 4: Verify Updated Permission Bits
Run `ls -l welcome.txt` to confirm the permissions now display as `-rw-------`.
💡 Pro Tip:
Avoid using `chmod 777` in production servers as it grants world-writable permissions, introducing severe security vulnerabilities.
bash — terminal
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