du (disk usage by directory) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

What is the output of this du command?

You run the command du -sh /var/log on a Linux system. What does the output represent?

Linux CLI

du -sh /var/log

A The total disk space used by the /var/log directory and all its contents, shown in a human-readable format.

B The free disk space available on the partition containing /var/log.

C The number of files inside /var/log directory.

D The size of the largest file inside /var/log.

💡 Hint

Think about what the options -s and -h mean in the du command.

The -s option summarizes the total size of the directory, and -h makes the output human-readable (like KB, MB). So the output shows total disk usage of /var/log.

💻 Command Output

intermediate

What does this command output?

You run du -h --max-depth=1 /home/user. What will the output show?

Linux CLI

du -h --max-depth=1 /home/user

A Only the total disk usage of /home/user without details.

B Disk usage of all files inside /home/user recursively, one line per file.

C Disk usage of /home/user and each of its immediate subdirectories, in human-readable form.

D Disk usage of /home/user but excluding hidden files.

💡 Hint

The --max-depth=1 limits how deep du reports.

The --max-depth=1 option tells du to show sizes for the directory and its immediate children only, not deeper nested folders.

🔧 Debug

advanced

Why does this du command fail?

You try to run du -h --maxdepth=1 /etc but get an error. What is the cause?

Linux CLI

du -h --maxdepth=1 /etc

A The option should be spelled <code>--max-depth</code> with a hyphen, not <code>--maxdepth</code>.

B The directory /etc does not exist.

C The <code>-h</code> option cannot be combined with <code>--maxdepth</code>.

D You need root permissions to run du on /etc.

💡 Hint

Check the spelling of the option carefully.

The correct option is --max-depth with a hyphen. Using --maxdepth causes an unrecognized option error.

🚀 Application

advanced

How to find the top 3 largest subdirectories in /var?

You want to list the three largest subdirectories inside /var by disk usage. Which command will do this?

A du -sh /var/* | sort -h | tail -n 3

B du -h /var | sort -h | head -n 3

C du -sh /var | sort -hr | head -n 3

D du -h --max-depth=1 /var | sort -hr | head -n 3

💡 Hint

Use du with max-depth to get sizes of immediate subdirectories, then sort and pick top 3.

du -h --max-depth=1 /var lists sizes of /var and its immediate subdirectories. Sorting numerically in reverse order with sort -hr puts largest first. head -n 3 picks top three.

🧠 Conceptual

expert

What is the effect of using du -b compared to du -h?

You run du -b /tmp and du -h /tmp. What is the difference in their outputs?

A <code>du -b</code> shows sizes in bits, <code>du -h</code> shows sizes in bytes.

B <code>du -b</code> shows disk usage in bytes (exact number), while <code>du -h</code> shows sizes in human-readable units like KB or MB.

C <code>du -b</code> shows sizes rounded to nearest KB, <code>du -h</code> shows exact bytes.

D <code>du -b</code> shows block counts, <code>du -h</code> shows bytes.

💡 Hint

Think about what the -b and -h options mean for size units.

-b means show size in bytes (exact count). -h means human-readable format with units like KB, MB, GB for easier reading.

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