✅ Update progress: Ex3 complete, permissions cheat sheet added

Midori's Linux Dojo 🌸/Phase 1 - Walking/Exercises.md

@@ -133,10 +133,25 @@ vi /root/lab/notes/vi-practice.txt
 
 ---
 
+### 💡 Key Lesson: Root bypasses everything!
+- **root** can read/write/execute ANY file regardless of permissions
+- Permissions only protect against **non-root users**
+- Always use a regular user + `sudo` in production!
+- Directories need `+x` to be accessible
+
+### 🔢 Permission Cheat Sheet
+| Mode | Octal | Meaning |
+|------|-------|---------|
+| `rwx------` | `700` | Only owner can do anything |
+| `rwxr-xr-x` | `755` | Owner full, others read+execute |
+| `rw-r--r--` | `644` | Readable by all, writable by owner |
+| `rw-------` | `600` | Only owner can read/write |
+| `rw-rw-rw-` | `666` | Everyone can read/write (dangerous!) |
+
 ## ✅ Phase 1 Complete Checklist
-- [ ] Exercise 1: `whoami`, `uname -a`, file creation
-- [ ] Exercise 2: Directory structure, `cp`, `mv`, `cat`
-- [ ] Exercise 3: `chmod`, permissions understanding
-- [ ] Exercise 4: Text editors (nano + vi)
+- [x] Exercise 1: `whoami`, `uname -a`, file creation
+- [x] Exercise 2: Directory structure, `cp`, `mv`, `cat`
+- [x] Exercise 3: `chmod`, permissions understanding
+- ⏭️ Exercise 4: Skipped (already know text editors)
 
 **Next:** [[Phase 2 - Networking]] 🌐