du (disk usage by directory) in Linux CLI - Step-by-Step Execution

Concept Flow - du (disk usage by directory)

Start du command

↓

Read directory contents

↓

Calculate size of each file

↓

Sum sizes per directory

↓

Display sizes

↓

End

The du command reads directory contents, calculates file sizes, sums them per directory, and displays the disk usage.

Execution Sample

Linux CLI

du -sh /home/user/Documents

Shows the total disk usage of the Documents directory in a human-readable format.

Execution Table

Step	Action	Directory/File	Size Calculated	Output
1	Start du command	/home/user/Documents
2	Read directory contents	/home/user/Documents
3	Calculate size	/home/user/Documents/file1.txt	4K
4	Calculate size	/home/user/Documents/file2.pdf	12M
5	Read directory contents	/home/user/Documents/Subfolder
6	Calculate size	/home/user/Documents/Subfolder/file3.jpg	2M
7	Sum sizes	/home/user/Documents/Subfolder	2M
8	Sum sizes	/home/user/Documents	14M
9	Display total size	/home/user/Documents	14M	14M /home/user/Documents

💡 All files and subdirectories processed, total size displayed.

Variable Tracker

Variable	Start	After Step 3	After Step 4	After Step 6	After Step 7	After Step 8	Final
Current File/Dir		/home/user/Documents/file1.txt	/home/user/Documents/file2.pdf	/home/user/Documents/Subfolder/file3.jpg	/home/user/Documents/Subfolder	/home/user/Documents
Size Calculated		4K	12M	2M	2M	14M	14M

Key Moments - 2 Insights

Why does du show sizes for subdirectories separately before summing?

du calculates sizes for each file and subdirectory first (see steps 3-6), then sums them up (steps 7-8) to show total usage.

What does the -h option do in du -sh?

The -h option makes sizes human-readable (like 4K, 12M) instead of bytes, making it easier to understand the output (step 9).

Visual Quiz - 3 Questions

Look at the execution table, what size is calculated for /home/user/Documents/file2.pdf at step 4?

A 12M

B 4K

C 2M

D 14M

💡 Hint

Check the 'Size Calculated' column at step 4 in the execution_table.

At which step does du sum the sizes of the Subfolder directory?

A Step 5

B Step 6

C Step 7

D Step 8

💡 Hint

Look for the 'Sum sizes' action related to Subfolder in the execution_table.

If the -h option was removed, how would the output at step 9 change?

A Sizes would be shown in megabytes only

B Sizes would be shown in bytes instead of human-readable units

C Output would include file names only

D Output would be sorted alphabetically

💡 Hint

The -h option controls human-readable size formatting as seen in the execution_sample description.

Concept Snapshot

du command shows disk usage of directories.
Syntax: du [options] [directory]
-h shows sizes in human-readable form.
-s shows total size only.
Reads files, sums sizes, displays result.

Full Transcript

The du command calculates disk usage by reading directory contents, measuring each file's size, summing sizes for subdirectories, and then displaying the total size. Using options like -h makes the output easier to read by showing sizes in KB, MB, etc. The process starts by reading files, calculating sizes step-by-step, summing them, and finally printing the total usage. This helps users understand how much space a directory and its contents occupy on disk.

Practice

1. What does the du command primarily show in Linux?

easy

A. The disk space used by files and directories

B. The number of files in a directory

C. The current directory path

D. The list of running processes

Solution

1. Step 1: Understand the purpose of du

   The du command stands for disk usage and shows how much space files and directories use.

2. Step 2: Compare options

   Options B, C, and D relate to other commands like ls or ps, not du.

3. Final Answer:

   The disk space used by files and directories -> Option A

4. Quick Check:

   du = disk space used [OK]

Hint: Remember: du = disk usage, shows space used [OK]

Common Mistakes:

• Confusing du with ls or ps commands
• Thinking du shows file counts
• Assuming du shows current directory path

2. Which du command option shows sizes in a human-readable format?

easy

A. -s

B. -c

C. -a

D. -h

Solution

1. Step 1: Identify the option for human-readable sizes

   The -h option makes sizes easier to read by adding units like K, M, G.

2. Step 2: Understand other options

   -s summarizes, -a shows all files, -c adds a total line.

3. Final Answer:

   -h -> Option D

4. Quick Check:

   -h = human-readable sizes [OK]

Hint: Use -h for sizes like KB, MB, GB [OK]

Common Mistakes:

• Using -s expecting human-readable sizes
• Confusing -a or -c with size formatting
• Omitting the -h option for readability

3. What is the output of the command du -sh /var/log if the /var/log directory uses 120M of disk space?

medium

A. 120M

B. 120M /var/log

C. 120MB /var/log

D. 120 /var/log

Solution

1. Step 1: Understand the command options

   -s summarizes total size, -h shows human-readable format.

2. Step 2: Predict output format

   The output shows size with unit, a tab, then directory path: "120M\t/var/log".

3. Final Answer:

   120M /var/log -> Option B

4. Quick Check:

   du -sh output = size + tab + path [OK]

Hint: du -sh shows size and path separated by tab [OK]

Common Mistakes:

• Omitting the tab separator
• Writing size without unit
• Showing size without path

4. You run du -h /home/user but get an error: "du: invalid option -- 'h'". What is the likely cause?

medium

A. The directory /home/user does not exist

B. You need to run the command as root

C. The du command does not support the -h option on this system

D. You must use --human-readable instead of -h

Solution

1. Step 1: Analyze the error message

   The error says -h is invalid, meaning this du version lacks that option.

2. Step 2: Check other options

   Running as root or directory existence wouldn't cause invalid option error; -h is standard, no need for long form.

3. Final Answer:

   The du command does not support the -h option on this system -> Option C

4. Quick Check:

   Invalid option error means unsupported flag [OK]

Hint: Invalid option means your du version lacks that flag [OK]

Common Mistakes:

• Assuming permission or path errors cause invalid option
• Trying --human-readable instead of checking version
• Ignoring error message details

5. You want to find the total disk usage of all subdirectories inside /home/user but only see sizes for individual files. Which command correctly summarizes each subdirectory size in human-readable form?

hard

A. du -sh /home/user/*

B. du -ah /home/user

C. du -h /home/user

D. du -s /home/user

Solution

1. Step 1: Understand the goal

   You want sizes of each subdirectory summarized, not individual files.

2. Step 2: Analyze options

   du -ah shows all files and dirs, du -sh on directory alone summarizes total only, du -s no human-readable. du -sh /home/user/* summarizes each subdirectory separately in human-readable form.

3. Final Answer:

   du -sh /home/user/* -> Option A

4. Quick Check:

   Use du -sh with wildcard for each subdir [OK]

Hint: Use du -sh with * to summarize each subdirectory [OK]

Common Mistakes:

• Using -a to include files instead of just dirs
• Using -s alone for total only
• Not using wildcard to list subdirectories