dmesg for kernel messages in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to display the kernel ring buffer messages.

Linux CLI

sudo [1]

Drag options to blanks, or click blank then click option'

Admesg

Btop

Cls

Dcat

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ls' or 'cat' instead of 'dmesg'.

Forgetting to use 'sudo' when required.

The command 'dmesg' shows the kernel ring buffer messages.

2fill in blank

medium

Complete the command to show kernel messages with human-readable timestamps.

Linux CLI

sudo dmesg [1]

Drag options to blanks, or click blank then click option'

A-n

B-w

C-c

D-T

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-n' which sets the log level.

Using '-c' which clears the buffer after printing.

The '-T' option shows timestamps in human-readable format.

3fill in blank

hard

Fix the error in the command to continuously watch kernel messages.

Linux CLI

sudo dmesg [1]

Drag options to blanks, or click blank then click option'

A-T

B-n

C-w

D-c

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-c' which clears the buffer instead of watching.

Using '-n' which sets log level, not watching.

The '-w' option makes dmesg wait and print new messages as they appear.

4fill in blank

hard

Fill in the blank to filter kernel messages by log level 3 (errors only).

Linux CLI

sudo dmesg [1] 3

Drag options to blanks, or click blank then click option'

A-l

B-T

C-n

D-w

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-n' which sets the console log level but does not filter dmesg output.

Using '-w' which watches messages instead of filtering.

Using '-T' which changes timestamp format.

The '-l' option filters the output to messages of the specified log levels, like 3 for errors.

5fill in blank

hard

Fill all three blanks to clear the kernel ring buffer and then show messages.

Linux CLI

sudo dmesg [1] && sudo dmesg [2] [3]

Drag options to blanks, or click blank then click option'

A-c

B-T

C-w

D-n

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-n' instead of '-w' for watching.

Not clearing before watching.

Use '-c' to clear the buffer, then '-T' for readable timestamps and '-w' to watch new messages.

Practice

1. What is the primary purpose of the dmesg command in Linux?

easy

A. To display kernel messages and system events

B. To list all running processes

C. To show disk usage statistics

D. To edit system configuration files

Solution

1. Step 1: Understand the role of dmesg

   The dmesg command reads the kernel ring buffer, which contains messages about system events and hardware status.

2. Step 2: Compare with other options

   Options A, B, and C relate to file editing, process listing, and disk usage, which are unrelated to kernel messages.

3. Final Answer:

   To display kernel messages and system events -> Option A

4. Quick Check:

   Kernel messages = display with dmesg [OK]

Hint: dmesg always shows kernel logs, not processes or files [OK]

Common Mistakes:

• Confusing dmesg with ps or top commands
• Thinking dmesg edits files
• Assuming dmesg shows disk info

2. Which of the following is the correct syntax to display kernel messages with human-readable timestamps using dmesg?

easy

A. dmesg -r

B. dmesg --time

C. dmesg -T

D. dmesg -h

Solution

1. Step 1: Identify the option for readable timestamps

   The -T option in dmesg converts kernel timestamps to human-readable format.

2. Step 2: Verify other options

   -r reverses output order, --time is invalid, and -h shows help.

3. Final Answer:

   dmesg -T -> Option C

4. Quick Check:

   Readable time = -T option [OK]

Hint: Use -T for readable timestamps in dmesg output [OK]

Common Mistakes:

• Using -r instead of -T for timestamps
• Typing invalid options like --time
• Confusing -h (help) with timestamp option

3. What will be the output of the command dmesg | grep usb?

medium

A. All kernel messages containing the word 'usb'

B. Only USB device names without any messages

C. A list of all running USB processes

D. An error because grep cannot be used with dmesg

Solution

1. Step 1: Understand the pipe and grep usage

   The command pipes dmesg output to grep usb, filtering lines containing 'usb'.

2. Step 2: Interpret the filtered output

   This shows kernel messages related to USB devices or events, not just names or processes.

3. Final Answer:

   All kernel messages containing the word 'usb' -> Option A

4. Quick Check:

   dmesg | grep filters messages by keyword [OK]

Hint: Pipe dmesg to grep to filter messages by keyword [OK]

Common Mistakes:

• Thinking grep lists processes
• Expecting only device names without messages
• Assuming grep causes errors with dmesg

4. You run dmesg -T but get an error saying "dmesg: option requires an argument -- 'T'". What is the likely cause?

medium

A. You typed the command incorrectly; -T needs a filename

B. You used an older dmesg version that does not support -T

C. The kernel is not loaded, so dmesg fails

D. You need root permissions to use -T option

Solution

1. Step 1: Analyze the error message

   The error says the option -T requires an argument, which is unusual because -T normally needs none.

2. Step 2: Understand version compatibility

   Older versions of dmesg do not support -T, causing this error.

3. Final Answer:

   You used an older dmesg version that does not support -T -> Option B

4. Quick Check:

   Old dmesg versions lack -T support [OK]

Hint: Check dmesg version if -T option errors [OK]

Common Mistakes:

• Assuming -T needs a filename argument
• Thinking root permission is required for -T
• Blaming kernel load status for this error

5. You want to monitor new kernel messages related to network devices in real-time. Which command combination is best?

hard

A. dmesg --follow --filter=net

B. dmesg -T | grep net

C. dmesg | tail -n 10 | grep net

D. dmesg -w | grep net

Solution

1. Step 1: Identify real-time monitoring option

   The -w option makes dmesg wait and show new messages as they appear.

2. Step 2: Combine with grep for filtering

   Piping to grep net filters messages related to network devices.

3. Step 3: Evaluate other options

   -T shows timestamps but is not real-time; tail -n 10 shows only last 10 lines; --follow --filter=net is invalid syntax.

4. Final Answer:

   dmesg -w | grep net -> Option D

5. Quick Check:

   Real-time dmesg = -w with grep filter [OK]

Hint: Use dmesg -w for live kernel logs, pipe to grep to filter [OK]

Common Mistakes:

• Using -T for real-time (it only formats time)
• Using tail only shows past logs, not live
• Assuming --follow or --filter options exist