df (disk free space) in Linux CLI - Commands & Configuration

Introduction

Sometimes your computer's storage gets full and you need to check how much space is left. The df command shows you the free and used disk space on your drives so you can manage your files better.

When you want to see how much space is left on your hard drive before saving large files.

When your computer warns you about low disk space and you want to find which drive is full.

When you are cleaning up files and want to check if deleting files freed enough space.

When you want to monitor disk usage on a server to avoid running out of space.

When you want to check the size of mounted drives like USB sticks or external disks.

Commands

This command shows disk space usage for all mounted filesystems in blocks. It gives a quick overview of used and available space.

Terminal

df

Expected Output

Filesystem     1K-blocks    Used Available Use% Mounted on

/dev/sda1      20511356 12345678   7156678  64% /

This command shows disk space usage in a human-readable format, using KB, MB, or GB so it's easier to understand.

Terminal

df -h

Expected Output

Filesystem      Size  Used Avail Use% Mounted on

/dev/sda1        20G   12G  6.8G  64% /

→

-h - Show sizes in human-readable format (KB, MB, GB)

This command adds the type of filesystem (like ext4 or tmpfs) to the output, helping you know what kind of storage is used.

Terminal

df -T

Expected Output

Filesystem     Type     1K-blocks    Used Available Use% Mounted on

/dev/sda1      ext4     20511356 12345678   7156678  64% /

→

-T - Display filesystem type

This command shows disk usage only for the /home directory, useful when you want to check space on a specific folder's drive.

Terminal

df -h /home

Expected Output

Filesystem      Size  Used Avail Use% Mounted on

/dev/sda2        50G   30G   18G  63% /home

Key Concept

If you remember nothing else from this pattern, remember: df shows how much disk space is used and free on your drives so you can manage storage.

Common Mistakes

Running df without -h and expecting easy-to-read sizes

The output shows sizes in blocks which are hard to understand quickly.

Use df -h to see sizes in KB, MB, or GB for easier reading.

Using df on a directory without knowing it shows the filesystem containing that directory

You might think it shows only that folder's size, but it shows the whole drive's usage.

Understand df reports disk usage per filesystem, not per folder size.

Summary

Use df to check disk space usage on all mounted filesystems.

Add -h flag to see sizes in human-readable format like MB or GB.

Use -T flag to see the type of filesystem for each mount point.

You can specify a directory to see disk usage for its filesystem only.

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