tail -f for live log monitoring in Linux CLI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to continuously watch the end of a log file named app.log.

Linux CLI

tail [1] app.log

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

A-f

B-c

C-n

D-v

Attempts:

3 left

💡 Hint

Common Mistakes

Using -n shows last lines but does not follow live updates.

Using -c shows bytes, not lines.

Using -v is for verbose output, not live monitoring.

The -f option tells tail to follow the file as it grows, showing new lines live.

2fill in blank

medium

Complete the command to follow server.log and show the last 20 lines initially.

Linux CLI

tail [1] 20 -f server.log

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

A-n

B-c

C-v

D-q

Attempts:

3 left

💡 Hint

Common Mistakes

Using -c shows bytes, not lines.

Using -v or -q do not control line count.

The -n option specifies the number of lines to show from the end before following.

3fill in blank

hard

Fix the error in the command to follow error.log live: tail -n -f 10 error.log. Place the correct option to make it work.

Linux CLI

tail [1] 10 error.log

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

A-n

B-n -f

C-f -n

D-f

Attempts:

3 left

💡 Hint

Common Mistakes

Putting -n before -f without a number causes errors.

Using only -f shows last 10 lines by default, but here 10 lines are requested.

The correct order is -f -n 10 so tail follows the file and shows last 10 lines initially.

4fill in blank

hard

Fill both blanks to create a command that follows access.log and shows the last 50 lines initially.

Linux CLI

tail [1] [2] -f access.log

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

A-f

B-n

C50

D-v

Attempts:

3 left

💡 Hint

Common Mistakes

Putting the number before the option.

Using -v which does not control lines or following.

The -n option with 50 before -f shows the last 50 lines initially and then follows the file live.

5fill in blank

hard

Fill all three blanks to create a command that follows debug.log, shows last 30 lines, and uses verbose output.

Linux CLI

tail [1] [2] [3] -f debug.log

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

A-f

B-n

C30

D-v

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the verbose option.

Placing the number before the -n option.

The -v option enables verbose output, -n 30 shows last 30 lines, and -f follows the file. Here verbose is placed first.

Practice

1. What does the command tail -f /var/log/syslog do?

easy

A. Copies the syslog file to another location

B. Deletes the syslog file permanently

C. Shows the last lines of the syslog file and updates live as new lines are added

D. Shows the first lines of the syslog file only once

Solution

1. Step 1: Understand the tail command

   The tail command shows the last part of a file.

2. Step 2: Understand the -f option

   The -f option makes tail keep running and show new lines as they are added to the file.

3. Final Answer:

   Shows the last lines of the syslog file and updates live as new lines are added -> Option C

4. Quick Check:

   tail -f = live log monitoring [OK]

Hint: Remember: -f means follow new lines live [OK]

Common Mistakes:

• Thinking tail -f deletes or copies files
• Confusing tail with head
• Expecting tail -f to show the start of the file

2. Which of the following is the correct syntax to continuously monitor the file /var/log/auth.log using tail?

easy

A. tail -n /var/log/auth.log

B. tail /var/log/auth.log -f

C. tail -follow /var/log/auth.log

D. tail -f /var/log/auth.log

Solution

1. Step 1: Identify correct option placement

   The option -f must come immediately after tail before the filename.

2. Step 2: Verify option correctness

   -f is the correct option to follow the file live; -follow is invalid and -n requires a number.

3. Final Answer:

   tail -f /var/log/auth.log -> Option D

4. Quick Check:

   Correct syntax = tail -f /var/log/auth.log [OK]

Hint: Options come before filename; -f not -follow [OK]

Common Mistakes:

• Placing options after filename
• Using invalid option -follow
• Using -n without a number

3. You run tail -f /var/log/app.log and see the following output after new log entries are added:

ERROR: Connection failed
INFO: Retrying connection
SUCCESS: Connected

What does this output indicate?

medium

A. The application is logging connection attempts and success live

B. The log file is empty and no new entries are added

C. The command failed to read the log file

D. The log file is being deleted while monitoring

Solution

1. Step 1: Understand tail -f output

   The command shows new lines added live to the log file.

2. Step 2: Interpret the log messages

   The messages show connection failure, retry, and success, indicating live logging of connection status.

3. Final Answer:

   The application is logging connection attempts and success live -> Option A

4. Quick Check:

   Live log updates = The application is logging connection attempts and success live [OK]

Hint: New lines mean live updates from the app log [OK]

Common Mistakes:

• Thinking the log file is empty
• Assuming command failed without error message
• Confusing deletion with normal log updates

4. You try to run tail -f /var/log/app.log but get the error: tail: cannot open '/var/log/app.log' for reading: Permission denied. What should you do to fix this?

medium

A. Delete the log file and try again

B. Run the command with sudo to get permission

C. Use head -f instead

D. Restart the system to fix permissions

Solution

1. Step 1: Understand the error message

   The error says permission denied, meaning the current user cannot read the file.

2. Step 2: Fix permission issue

   Running the command with sudo gives temporary admin rights to read the file.

3. Final Answer:

   Run the command with sudo to get permission -> Option B

4. Quick Check:

   Permission denied fix = use sudo [OK]

Hint: Permission denied? Try sudo before the command [OK]

Common Mistakes:

• Deleting the log file unnecessarily
• Using head -f which is invalid
• Restarting system without checking permissions

5. You want to monitor two log files live at the same time: /var/log/nginx/access.log and /var/log/nginx/error.log. Which command will correctly do this?

hard

A. tail -f /var/log/nginx/access.log /var/log/nginx/error.log

B. tail -f /var/log/nginx/access.log && tail -f /var/log/nginx/error.log

C. tail -f /var/log/nginx/access.log | tail -f /var/log/nginx/error.log

D. tail -f /var/log/nginx/access.log; tail -f /var/log/nginx/error.log

Solution

1. Step 1: Understand how to monitor multiple files

   tail -f accepts multiple filenames to follow them simultaneously in one terminal.

2. Step 2: Analyze each option

   tail -f /var/log/nginx/access.log /var/log/nginx/error.log correctly lists both files after tail -f. Using && or ; runs commands sequentially, so the second starts after the first ends. Piping two tail -f commands with | is invalid for this purpose.

3. Final Answer:

   tail -f /var/log/nginx/access.log /var/log/nginx/error.log -> Option A

4. Quick Check:

   Multiple files = list all after tail -f [OK]

Hint: List all files after tail -f to watch together [OK]

Common Mistakes:

• Using && or ; runs commands one after another, not together
• Piping two tail -f commands is invalid
• Trying to monitor files separately in one terminal