A+ Lab 7 — PC Won’t Boot: Power, POST, or OS?

by

ITF+ Virtual Machine Lab Series — Lesson 7: Storage & File System Troubleshooting

Fix two of the most common real-world problems: Disk Full and Permission Denied.

Difficulty: Beginner Time: 45–70 min Tools: df, du, ls -la, chmod, chown
Skill: Prove disk usage Skill: Find large folders Skill: Clean safely Skill: Read permissions Skill: Fix ownership
Real tickets: “Updates fail” • “I can’t save files” • “Permission denied” • “No space left on device”
This lab teaches proof-first troubleshooting: measure → locate → fix → verify.

Fast Triage (read the symptom → pick the right test)

Disk Full vs Permission Denied
Two commands solve 80% of cases
If you see: No space left on device / updates fail / apps won’t install
Test: show filesystem usage.
df -h  then  du -h –max-depth=1 ~
If you see: Permission denied / cannot write / cannot open
Test: check owner + permissions on the path.
ls -la  then  stat <file>
Safety note: We are not going to delete system folders. You’ll clean safely and learn what’s safe vs risky.
If you want to simulate “disk full,” we do it in your home folder only.

Lab flow (click to reveal)

Run:

df -h
  • Focus on the line for / (root filesystem).
  • 90%+ usage can cause slow updates, install failures, and weird app behavior.

Write down your root usage:

  • / Used%: __________

Find large folders in your home directory:

du -h –max-depth=1 ~ | sort -h

Want to check downloads specifically?

du -h –max-depth=1 ~/Downloads | sort -h
Technician habit:
Use df to prove “full”, then du to find the culprit folder.
Optional simulation:
This creates a large file in your home folder only. If you’re low on space already, skip this step.

Create a 1GB file (safe to delete later):

cd ~ fallocate -l 1G bigfile.bin

Now re-check disk usage:

df -h du -h –max-depth=1 ~ | sort -h

These are safe, common cleanup commands:

sudo apt clean sudo apt autoremove -y

If you created the big file, delete it:

rm -f ~/bigfile.bin

Verify usage improved:

df -h
Rule:
Clean caches and remove unused packages before deleting random system folders.

In Linux, files have:

  • Owner (user)
  • Group
  • Permissions (r/w/x) for owner, group, others

Try:

cd ~ ls -la
How to read it:
Example: -rw-r–r– means owner can read/write, group can read, others can read.

Create a folder owned by root inside your home (safe, reversible):

mkdir -p ~/locked_lab sudo chown root:root ~/locked_lab sudo chmod 700 ~/locked_lab

Now try to write a file (this should fail):

echo “test” > ~/locked_lab/try.txt

You should see Permission denied. Next step fixes it the right way.

Best fix: give the folder back to your user (replace USER with your username):

whoami sudo chown -R <USER>:<USER> ~/locked_lab sudo chmod 755 ~/locked_lab

Now try again:

echo “test” > ~/locked_lab/try.txt cat ~/locked_lab/try.txt
When to use sudo vs chown?
If it’s your folder in your home, fixing ownership is cleaner than always using sudo.

Practical: Ticket Triage (Disk vs Permissions)

Pick a category, then reveal the correct diagnosis + proof command.
Goal: 5/6 correct
Ticket 1: “Ubuntu updates fail with ‘No space left on device’.”
Correct: Disk Full. Prove with df -h, locate with du.
Ticket 2: “I can open the file but can’t save changes — Permission denied.”
Correct: Permissions. Check owner/perms with ls -la or stat.
Ticket 3: “Browser won’t download files. It says ‘Disk full’.”
Correct: Disk Full. Verify with df -h. Downloads often fill ~/Downloads.
Ticket 4: “I get ‘Permission denied’ writing to a folder in my home directory.”
Correct: Permissions. Fix ownership with chown if it’s your folder.
Ticket 5: “Internet works, but installs fail with ‘Temporary failure resolving’.”
Correct: Other (DNS). Prove with ping 8.8.8.8 vs nslookup.
Ticket 6: “System is slow and keeps freezing during updates.”
Often Disk Full or Low RAM. Check df -h and Lesson 3 (top).
Score: —

Before / After Results (fill this in)

Check Before After
/ Used% (from df) __________ __________
Largest folder found (from du) __________ __________
Cleanup actions (apt clean, rm, etc.) __________
Permission fix command __________
If you get stuck (Reset / Recovery)
This returns your lab folder back to normal and cleans safely.
# Delete the test folder if you want: rm -rf ~/locked_lab # Safe cleanup: sudo apt clean sudo apt autoremove -y # Check disk again: df -h

Mini Quiz (10 Questions)

Instant feedback • Storage + permissions basics
Pass target: 8/10

1) Which command shows disk usage by filesystem (including /)?

df reports filesystem usage. -h makes it human-readable.

2) Which command helps you find which folder is taking the most space?

du summarizes directory usage; max-depth helps you see “top folders.”

3) “No space left on device” most commonly means:

It usually indicates the partition you’re writing to is out of space.

4) Which command is a safe way to clear cached package files?

apt clean removes cached .deb files and is a common safe cleanup step.

5) “Permission denied” usually means:

It’s about access rights: ownership or permission bits.

6) Which command shows file permissions and ownership in a directory?

ls -la shows permissions, owner, group, and more.

7) Which command changes file ownership?

chown changes owner (and optionally group).

8) chmod primarily changes:

chmod modifies permissions, not ownership.

9) If disk is 95% full, updates and installs may fail because:

Package managers need room to download, unpack, and write logs/temp files.

10) Best proof that you fixed a disk-full problem?

Verification is measurement + symptom resolved.
Score: —
CCP VM Lab Series • Lesson 7 • Storage & File System Troubleshooting
Cheat Sheet Save
  • df -h → disk usage by filesystem
  • du -h –max-depth=1 ~ → largest folders in home
  • sudo apt clean → clear apt cache
  • sudo apt autoremove -y → remove unused packages
  • ls -la → permissions + ownership
  • chown → change owner
  • chmod → change permissions
What’s safe to delete? Rules
  • ✅ Large downloads in ~/Downloads
  • ✅ Big temp files in your home folder
  • ✅ apt cache (via sudo apt clean)
  • ⚠️ Avoid deleting random folders in /
ITF+ Mapping Exam-ready
  • Storage concepts: partitions, disk usage, free space
  • File system: directories, files, permissions
  • Troubleshooting: measure → locate → fix → verify
UTM note Mac

If your VM disk is too small, even normal updates can fill it. Consider increasing the VM storage size in UTM for long-term labs.

Leave a Comment