Chapter 30: Bash Directory Usage (du)

What does du actually do? (super simple first)

du = disk usage It tells you how much space each folder (and its contents) is using on your disk.

Key difference from df:

• df → shows total/used/available per partition/drive (big picture)
• du → shows how much space each folder/file/subfolder is using (detailed breakdown)

Without du, you see /home is 200 GB full in df, but you don’t know which folder inside /home is the big culprit (Downloads? Videos? .cache? node_modules?).

du helps you hunt down space hogs so you can clean up safely.

1. Basic usage (try right now!)

This shows space used by every folder in your home directory (and subfolders) in 1K-blocks (1024 bytes each) – very hard to read!

Better – always use these flags together:

• -s = summary (only show total for the folder you asked)
• -h = human-readable (shows KB, MB, GB, TB instead of blocks)

Example output you might see:

2. Most useful combinations (you’ll use these 95% of time)

Try this right now (very useful!):

Example output:

Now you know exactly where to clean first!

3. Very common flags explained (learn these!)

4. Real-life examples (Hyderabad developer style)

• Laptop saying disk full when downloading movies?
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  du -sh ~/Downloads/* | sort -hr | head -5 # → delete old .zip or .torrent files

• VS Code / Node.js project eating space?
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  du -sh node_modules | sort -hr # → 4.8G node_modules → rm -rf node_modules && npm ci

• Where are all my Python virtualenvs?
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  du -sh ~/.virtualenvs/* | sort -hr | head -8

• Check Docker images / containers / volumes
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  sudo du -sh /var/lib/docker/* | sort -hr # → if huge → docker system prune -a --volumes

• Find biggest log files
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  sudo du -ah /var/log | sort -hr | head -15

• Quick space check before big git clone
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  du -sh .git 2>/dev/null || echo "No git repo here"

5. Quick cheat-sheet table

6. Pro tips from daily use

• du is slow on huge folders (e.g. millions of files) – be patient or use –max-depth
• Combine with sort -hr almost always (human-readable + reverse + numeric)
• Use sudo when checking /var, /usr, /opt
• du shows disk blocks used (can be more than file size due to block size) → use –apparent-size if you want actual file size
• Alternative modern tools: ncdu (install it – interactive ncurses du!)
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  sudo apt install ncdu ncdu ~ # → arrow keys, delete files inside it!

Now open your terminal and try these 3 right now:

Tell me:

• What’s the biggest folder in your home right now? (e.g. 28G Videos)
• Or ask: “How to find all files bigger than 1GB?” or “du vs df – when to use which?” or “How to use ncdu?”

We’ll solve it together! 😄