Checking Disk Usage with df and du: A Linux Admin’s Guide

Whether you’re managing a server or troubleshooting your Linux system, monitoring disk space is crucial. Two essential terminal commands—df and du—help you diagnose storage issues. Here’s how to use them like a pro.

1. df (Disk Free): The Big Picture

Purpose: Check overall disk usage for mounted filesystems (e.g., partitions, drives).
Syntax: df [options] [path]

Key Options & Examples:

• Basic Usage:

  df -h  # "-h": Human-readable sizes (KB, MB, GB)

  Output:

  Filesystem      Size  Used Avail Use% Mounted on  
  /dev/sda1        20G   11G  7.8G  58% /  
  tmpfs           3.9G     0  3.9G   0% /tmp  

• Show Filesystem Types (-T):

  df -Th  # Adds a "Type" column (ext4, tmpfs, etc.)

• Focus on Specific Filesystems (e.g., ext4):

  df -ht ext4  

2. du (Disk Usage): Deep Dive into Directories

Purpose: Measure directory-level usage (ideal for finding space hogs).
Syntax: du [options] [directory]

Key Options & Examples:

• Summarize Directory Usage (-s):

  du -sh /home  # "-s": Summary total, "-h": Human-readable

  Output: 24G /home

• List Subdirectory Sizes (Depth=1):

  du -h --max-depth=1 /var/log  

  Output:

  4.0K  /var/log/apt  
  800M  /var/log/journal  
  801M  /var/log  

• Find Large Files (Combine with sort):

  du -h /var | sort -rh | head -n 5  # Top 5 space-consuming dirs

3. When to Use Which

• Use df when:

  • You need a quick overview of mounted filesystems.
  • Checking if a partition is full (e.g., /dev/sda1 at 95%).

• Use du when:

  • You need to identify which directories/files consume space.
  • Auditing storage in /home, /var, or other user-data locations.

4. Pro Tips

• Exclude Hidden Files (e.g., .cache):

  du -sh --exclude=".*" /home/user  

• df Caveat: It reports filesystem metadata, so Used + Avail may not equal Size (reserved space exists).
• Combine Both:

  df -h /home      # Check partition usage  
  du -sh /home/*   # Then scan directories  

Conclusion

df gives you a helicopter view of disk health, while du drills into directory details. Together, they’re indispensable for:

• Preventing “out of space” crashes.
• Cleaning up bloated systems.
• Optimizing server storage.

Try these commands now! Run df -h and du -sh ~/ to start exploring your own disk usage. 🚀

> Note: Always use -h for readability, and prefix destructive commands (like rm) with sudo cautiously!