df (disk free space) in Linux CLI - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Understanding the output of df -h

What is the output of the command df -h on a typical Linux system?

Linux CLI

df -h

A Shows disk usage in human-readable format with sizes like 1K, 234M, 2G

B Shows only the total disk size without usage details

C Shows network usage statistics

D Shows a list of running processes and their disk usage

💡 Hint

The -h option means human-readable sizes.

The df -h command displays disk space usage with sizes in easy-to-read units like KB, MB, or GB.

💻 Command Output

intermediate

Output of df --total

What does the df --total command add to the usual df output?

Linux CLI

df --total

A Shows only the total size of the root filesystem

B Displays disk usage for network filesystems only

C Adds a summary line showing total disk usage across all filesystems

D Shows disk usage sorted by mount point name

💡 Hint

Look for a line labeled 'total' at the end.

The --total option adds a summary line that sums up all disk usage values from the listed filesystems.

📝 Syntax

advanced

Correct usage of df to show inode usage

Which command correctly shows inode usage with df?

A df -i

B df --inodes

C df -h -i

D df --inode-usage

💡 Hint

The option for inode info is a short flag.

The -i option shows inode usage. --inodes and --inode-usage are invalid options.

🔧 Debug

advanced

Why does df /nonexistent fail?

What error does the command df /nonexistent produce and why?

Linux CLI

df /nonexistent

A df: Invalid argument - because the path is not a mount point

B df: Permission denied - because the user lacks rights

C df: Device busy - because the path is in use

D df: /nonexistent: No such file or directory - because the path does not exist

💡 Hint

Check if the path exists before running df.

If the path does not exist, df cannot find the filesystem and returns a 'No such file or directory' error.

🚀 Application

expert

Automate disk usage alert with df

You want to write a script that alerts you if any mounted filesystem is more than 90% full. Which command pipeline correctly extracts the usage percentage and filters filesystems over 90%?

A df -h | grep -v Filesystem | awk '{if ($5 > 90) print $1, $5}'

B df -h | awk 'NR>1 {sub(/%/, "", $5); if ($5 > 90) print $1, $5"%"}'

C df | awk '{if ($5 > 90) print $1, $5}'

D df -h | awk '{if ($5+0 > 90) print $1, $5}'

💡 Hint

You need to remove the % sign before comparing numbers.

Option B removes the % sign from the 5th column and compares the numeric value correctly. Others either miss removing % or skip header properly.

Practice

1. What does the df command do in Linux?

easy

A. Shows disk free space on mounted filesystems

B. Displays running processes

C. Lists files in a directory

D. Shows network connections

Solution

1. Step 1: Understand the purpose of df

   The df command is used to report disk space usage on mounted filesystems.

2. Step 2: Compare with other commands

   Other options like listing processes or files are done by different commands like ps or ls.

3. Final Answer:

   Shows disk free space on mounted filesystems -> Option A

4. Quick Check:

   df = disk free space [OK]

Hint: Remember: df = disk free space quick check [OK]

Common Mistakes:

• Confusing df with ls or ps commands
• Thinking df shows network info
• Assuming df lists files

2. Which of these is the correct syntax to show disk space in human-readable format?

easy

A. df -r

B. df -h

C. df --list

D. df -x

Solution

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

   The -h option in df shows sizes in easy units like MB, GB.

2. Step 2: Check other options

   Options like -r, --list, or -x do not provide human-readable output.

3. Final Answer:

   df -h -> Option B

4. Quick Check:

   -h means human-readable [OK]

Hint: Use -h for human-readable sizes with df [OK]

Common Mistakes:

• Using -r or -x instead of -h
• Forgetting the dash before h
• Trying --list which is invalid

3. What will be the output of the command df -h /home?

medium

A. Shows disk usage of the /home filesystem in human-readable format

B. Shows disk usage of the root filesystem

C. Shows all mounted filesystems in bytes

D. Shows network disk usage

Solution

1. Step 1: Understand the command arguments

   The command df -h /home checks disk space for the /home directory only, with human-readable sizes.

2. Step 2: Eliminate other options

   It does not show root filesystem unless /home is on root, nor does it show all filesystems or network usage.

3. Final Answer:

   Shows disk usage of the /home filesystem in human-readable format -> Option A

4. Quick Check:

   df -h /home = /home usage human-readable [OK]

Hint: Add path after df -h to check specific folder space [OK]

Common Mistakes:

• Assuming it shows all filesystems
• Confusing /home with root filesystem
• Expecting output in bytes without -h

4. You run df -h /nonexistent and get an error. What is the likely cause?

medium

A. You need root permissions to run df

B. The df command does not support -h option

C. The path /nonexistent does not exist or is not mounted

D. The disk is full

Solution

1. Step 1: Analyze the error cause

   Running df on a path that does not exist or is not mounted causes an error.

2. Step 2: Check other options

   df supports -h, does not require root, and disk full does not cause this error.

3. Final Answer:

   The path /nonexistent does not exist or is not mounted -> Option C

4. Quick Check:

   Invalid path = error [OK]

Hint: Check if path exists before using df on it [OK]

Common Mistakes:

• Thinking -h is unsupported
• Assuming root needed for df
• Confusing disk full with path error

5. You want to check disk space for all mounted filesystems but exclude the tmpfs type. Which command will do this?

hard

A. df -h --exclude tmpfs

B. df -h --exclude=tmpfs

C. df -h --ignore-type tmpfs

D. df -h -x tmpfs

Solution

1. Step 1: Identify the correct option to exclude filesystem type

   The -x option excludes a filesystem type in df. So df -h -x tmpfs excludes tmpfs.

2. Step 2: Verify other options

   Options like --exclude-type, --exclude, or --ignore-type are invalid for df.

3. Final Answer:

   df -h -x tmpfs -> Option D

4. Quick Check:

   -x excludes filesystem type [OK]

Hint: Use -x to exclude filesystem types in df [OK]

Common Mistakes:

• Using invalid options like --exclude-type
• Confusing exclude with ignore
• Forgetting dash before x